Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/bpf_dsl/bpf_dsl_more_unittest.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/bpf_dsl/bpf_dsl.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <sys/prctl.h>
+#include <sys/ptrace.h>
+#include <sys/syscall.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/utsname.h>
+#include <unistd.h>
+#include <sys/socket.h>
+
+#if defined(ANDROID)
+// Work-around for buggy headers in Android's NDK
+#define __user
+#endif
+#include <linux/futex.h>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/threading/thread.h"
+#include "build/build_config.h"
+#include "sandbox/linux/seccomp-bpf/bpf_tests.h"
+#include "sandbox/linux/seccomp-bpf/die.h"
+#include "sandbox/linux/seccomp-bpf/errorcode.h"
+#include "sandbox/linux/seccomp-bpf/linux_seccomp.h"
+#include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
+#include "sandbox/linux/seccomp-bpf/syscall.h"
+#include "sandbox/linux/seccomp-bpf/trap.h"
+#include "sandbox/linux/services/broker_process.h"
+#include "sandbox/linux/services/linux_syscalls.h"
+#include "sandbox/linux/tests/scoped_temporary_file.h"
+#include "sandbox/linux/tests/unit_tests.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+// Workaround for Android's prctl.h file.
+#ifndef PR_GET_ENDIAN
+#define PR_GET_ENDIAN 19
+#endif
+#ifndef PR_CAPBSET_READ
+#define PR_CAPBSET_READ 23
+#define PR_CAPBSET_DROP 24
+#endif
+
+namespace sandbox {
+namespace bpf_dsl {
+
+namespace {
+
+const int kExpectedReturnValue = 42;
+const char kSandboxDebuggingEnv[] = "CHROME_SANDBOX_DEBUGGING";
+
+// Set the global environment to allow the use of UnsafeTrap() policies.
+void EnableUnsafeTraps() {
+  // The use of UnsafeTrap() causes us to print a warning message. This is
+  // generally desirable, but it results in the unittest failing, as it doesn't
+  // expect any messages on "stderr". So, temporarily disable messages. The
+  // BPF_TEST() is guaranteed to turn messages back on, after the policy
+  // function has completed.
+  setenv(kSandboxDebuggingEnv, "t", 0);
+  Die::SuppressInfoMessages(true);
+}
+
+// This test should execute no matter whether we have kernel support. So,
+// we make it a TEST() instead of a BPF_TEST().
+TEST(SandboxBPF, DISABLE_ON_TSAN(CallSupports)) {
+  // We check that we don't crash, but it's ok if the kernel doesn't
+  // support it.
+  bool seccomp_bpf_supported =
+      SandboxBPF::SupportsSeccompSandbox(-1) == SandboxBPF::STATUS_AVAILABLE;
+  // We want to log whether or not seccomp BPF is actually supported
+  // since actual test coverage depends on it.
+  RecordProperty("SeccompBPFSupported",
+                 seccomp_bpf_supported ? "true." : "false.");
+  std::cout << "Seccomp BPF supported: "
+            << (seccomp_bpf_supported ? "true." : "false.") << "\n";
+  RecordProperty("PointerSize", sizeof(void*));
+  std::cout << "Pointer size: " << sizeof(void*) << "\n";
+}
+
+SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(CallSupportsTwice)) {
+  SandboxBPF::SupportsSeccompSandbox(-1);
+  SandboxBPF::SupportsSeccompSandbox(-1);
+}
+
+// BPF_TEST does a lot of the boiler-plate code around setting up a
+// policy and optional passing data between the caller, the policy and
+// any Trap() handlers. This is great for writing short and concise tests,
+// and it helps us accidentally forgetting any of the crucial steps in
+// setting up the sandbox. But it wouldn't hurt to have at least one test
+// that explicitly walks through all these steps.
+
+intptr_t IncreaseCounter(const struct arch_seccomp_data& args, void* aux) {
+  BPF_ASSERT(aux);
+  int* counter = static_cast<int*>(aux);
+  return (*counter)++;
+}
+
+class VerboseAPITestingPolicy : public SandboxBPFDSLPolicy {
+ public:
+  explicit VerboseAPITestingPolicy(int* counter_ptr)
+      : counter_ptr_(counter_ptr) {}
+  virtual ~VerboseAPITestingPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    if (sysno == __NR_uname) {
+      return Trap(IncreaseCounter, counter_ptr_);
+    }
+    return Allow();
+  }
+
+ private:
+  int* counter_ptr_;
+
+  DISALLOW_COPY_AND_ASSIGN(VerboseAPITestingPolicy);
+};
+
+SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(VerboseAPITesting)) {
+  if (SandboxBPF::SupportsSeccompSandbox(-1) ==
+      sandbox::SandboxBPF::STATUS_AVAILABLE) {
+    static int counter = 0;
+
+    SandboxBPF sandbox;
+    sandbox.SetSandboxPolicy(new VerboseAPITestingPolicy(&counter));
+    BPF_ASSERT(sandbox.StartSandbox(SandboxBPF::PROCESS_SINGLE_THREADED));
+
+    BPF_ASSERT_EQ(0, counter);
+    BPF_ASSERT_EQ(0, syscall(__NR_uname, 0));
+    BPF_ASSERT_EQ(1, counter);
+    BPF_ASSERT_EQ(1, syscall(__NR_uname, 0));
+    BPF_ASSERT_EQ(2, counter);
+  }
+}
+
+// A simple blacklist test
+
+class BlacklistNanosleepPolicy : public SandboxBPFDSLPolicy {
+ public:
+  BlacklistNanosleepPolicy() {}
+  virtual ~BlacklistNanosleepPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    switch (sysno) {
+      case __NR_nanosleep:
+        return Error(EACCES);
+      default:
+        return Allow();
+    }
+  }
+
+  static void AssertNanosleepFails() {
+    const struct timespec ts = {0, 0};
+    errno = 0;
+    BPF_ASSERT_EQ(-1, HANDLE_EINTR(syscall(__NR_nanosleep, &ts, NULL)));
+    BPF_ASSERT_EQ(EACCES, errno);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BlacklistNanosleepPolicy);
+};
+
+BPF_TEST_C(SandboxBPF, ApplyBasicBlacklistPolicy, BlacklistNanosleepPolicy) {
+  BlacklistNanosleepPolicy::AssertNanosleepFails();
+}
+
+// Now do a simple whitelist test
+
+class WhitelistGetpidPolicy : public SandboxBPFDSLPolicy {
+ public:
+  WhitelistGetpidPolicy() {}
+  virtual ~WhitelistGetpidPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    switch (sysno) {
+      case __NR_getpid:
+      case __NR_exit_group:
+        return Allow();
+      default:
+        return Error(ENOMEM);
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WhitelistGetpidPolicy);
+};
+
+BPF_TEST_C(SandboxBPF, ApplyBasicWhitelistPolicy, WhitelistGetpidPolicy) {
+  // getpid() should be allowed
+  errno = 0;
+  BPF_ASSERT(syscall(__NR_getpid) > 0);
+  BPF_ASSERT(errno == 0);
+
+  // getpgid() should be denied
+  BPF_ASSERT(getpgid(0) == -1);
+  BPF_ASSERT(errno == ENOMEM);
+}
+
+// A simple blacklist policy, with a SIGSYS handler
+intptr_t EnomemHandler(const struct arch_seccomp_data& args, void* aux) {
+  // We also check that the auxiliary data is correct
+  SANDBOX_ASSERT(aux);
+  *(static_cast<int*>(aux)) = kExpectedReturnValue;
+  return -ENOMEM;
+}
+
+class BlacklistNanosleepTrapPolicy : public SandboxBPFDSLPolicy {
+ public:
+  explicit BlacklistNanosleepTrapPolicy(int* aux) : aux_(aux) {}
+  virtual ~BlacklistNanosleepTrapPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    switch (sysno) {
+      case __NR_nanosleep:
+        return Trap(EnomemHandler, aux_);
+      default:
+        return Allow();
+    }
+  }
+
+ private:
+  int* aux_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlacklistNanosleepTrapPolicy);
+};
+
+BPF_TEST(SandboxBPF,
+         BasicBlacklistWithSigsys,
+         BlacklistNanosleepTrapPolicy,
+         int /* (*BPF_AUX) */) {
+  // getpid() should work properly
+  errno = 0;
+  BPF_ASSERT(syscall(__NR_getpid) > 0);
+  BPF_ASSERT(errno == 0);
+
+  // Our Auxiliary Data, should be reset by the signal handler
+  *BPF_AUX = -1;
+  const struct timespec ts = {0, 0};
+  BPF_ASSERT(syscall(__NR_nanosleep, &ts, NULL) == -1);
+  BPF_ASSERT(errno == ENOMEM);
+
+  // We expect the signal handler to modify AuxData
+  BPF_ASSERT(*BPF_AUX == kExpectedReturnValue);
+}
+
+// A simple test that verifies we can return arbitrary errno values.
+
+class ErrnoTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  ErrnoTestPolicy() {}
+  virtual ~ErrnoTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ErrnoTestPolicy);
+};
+
+ResultExpr ErrnoTestPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  switch (sysno) {
+    case __NR_dup3:  // dup2 is a wrapper of dup3 in android
+#if defined(__NR_dup2)
+    case __NR_dup2:
+#endif
+      // Pretend that dup2() worked, but don't actually do anything.
+      return Error(0);
+    case __NR_setuid:
+#if defined(__NR_setuid32)
+    case __NR_setuid32:
+#endif
+      // Return errno = 1.
+      return Error(1);
+    case __NR_setgid:
+#if defined(__NR_setgid32)
+    case __NR_setgid32:
+#endif
+      // Return maximum errno value (typically 4095).
+      return Error(ErrorCode::ERR_MAX_ERRNO);
+    case __NR_uname:
+      // Return errno = 42;
+      return Error(42);
+    default:
+      return Allow();
+  }
+}
+
+BPF_TEST_C(SandboxBPF, ErrnoTest, ErrnoTestPolicy) {
+  // Verify that dup2() returns success, but doesn't actually run.
+  int fds[4];
+  BPF_ASSERT(pipe(fds) == 0);
+  BPF_ASSERT(pipe(fds + 2) == 0);
+  BPF_ASSERT(dup2(fds[2], fds[0]) == 0);
+  char buf[1] = {};
+  BPF_ASSERT(write(fds[1], "\x55", 1) == 1);
+  BPF_ASSERT(write(fds[3], "\xAA", 1) == 1);
+  BPF_ASSERT(read(fds[0], buf, 1) == 1);
+
+  // If dup2() executed, we will read \xAA, but it dup2() has been turned
+  // into a no-op by our policy, then we will read \x55.
+  BPF_ASSERT(buf[0] == '\x55');
+
+  // Verify that we can return the minimum and maximum errno values.
+  errno = 0;
+  BPF_ASSERT(setuid(0) == -1);
+  BPF_ASSERT(errno == 1);
+
+  // On Android, errno is only supported up to 255, otherwise errno
+  // processing is skipped.
+  // We work around this (crbug.com/181647).
+  if (sandbox::IsAndroid() && setgid(0) != -1) {
+    errno = 0;
+    BPF_ASSERT(setgid(0) == -ErrorCode::ERR_MAX_ERRNO);
+    BPF_ASSERT(errno == 0);
+  } else {
+    errno = 0;
+    BPF_ASSERT(setgid(0) == -1);
+    BPF_ASSERT(errno == ErrorCode::ERR_MAX_ERRNO);
+  }
+
+  // Finally, test an errno in between the minimum and maximum.
+  errno = 0;
+  struct utsname uts_buf;
+  BPF_ASSERT(uname(&uts_buf) == -1);
+  BPF_ASSERT(errno == 42);
+}
+
+// Testing the stacking of two sandboxes
+
+class StackingPolicyPartOne : public SandboxBPFDSLPolicy {
+ public:
+  StackingPolicyPartOne() {}
+  virtual ~StackingPolicyPartOne() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    switch (sysno) {
+      case __NR_getppid: {
+        const Arg<int> arg(0);
+        return If(arg == 0, Allow()).Else(Error(EPERM));
+      }
+      default:
+        return Allow();
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(StackingPolicyPartOne);
+};
+
+class StackingPolicyPartTwo : public SandboxBPFDSLPolicy {
+ public:
+  StackingPolicyPartTwo() {}
+  virtual ~StackingPolicyPartTwo() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    switch (sysno) {
+      case __NR_getppid: {
+        const Arg<int> arg(0);
+        return If(arg == 0, Error(EINVAL)).Else(Allow());
+      }
+      default:
+        return Allow();
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(StackingPolicyPartTwo);
+};
+
+BPF_TEST_C(SandboxBPF, StackingPolicy, StackingPolicyPartOne) {
+  errno = 0;
+  BPF_ASSERT(syscall(__NR_getppid, 0) > 0);
+  BPF_ASSERT(errno == 0);
+
+  BPF_ASSERT(syscall(__NR_getppid, 1) == -1);
+  BPF_ASSERT(errno == EPERM);
+
+  // Stack a second sandbox with its own policy. Verify that we can further
+  // restrict filters, but we cannot relax existing filters.
+  SandboxBPF sandbox;
+  sandbox.SetSandboxPolicy(new StackingPolicyPartTwo());
+  BPF_ASSERT(sandbox.StartSandbox(SandboxBPF::PROCESS_SINGLE_THREADED));
+
+  errno = 0;
+  BPF_ASSERT(syscall(__NR_getppid, 0) == -1);
+  BPF_ASSERT(errno == EINVAL);
+
+  BPF_ASSERT(syscall(__NR_getppid, 1) == -1);
+  BPF_ASSERT(errno == EPERM);
+}
+
+// A more complex, but synthetic policy. This tests the correctness of the BPF
+// program by iterating through all syscalls and checking for an errno that
+// depends on the syscall number. Unlike the Verifier, this exercises the BPF
+// interpreter in the kernel.
+
+// We try to make sure we exercise optimizations in the BPF compiler. We make
+// sure that the compiler can have an opportunity to coalesce syscalls with
+// contiguous numbers and we also make sure that disjoint sets can return the
+// same errno.
+int SysnoToRandomErrno(int sysno) {
+  // Small contiguous sets of 3 system calls return an errno equal to the
+  // index of that set + 1 (so that we never return a NUL errno).
+  return ((sysno & ~3) >> 2) % 29 + 1;
+}
+
+class SyntheticPolicy : public SandboxBPFDSLPolicy {
+ public:
+  SyntheticPolicy() {}
+  virtual ~SyntheticPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    if (sysno == __NR_exit_group || sysno == __NR_write) {
+      // exit_group() is special, we really need it to work.
+      // write() is needed for BPF_ASSERT() to report a useful error message.
+      return Allow();
+    }
+    return Error(SysnoToRandomErrno(sysno));
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SyntheticPolicy);
+};
+
+BPF_TEST_C(SandboxBPF, SyntheticPolicy, SyntheticPolicy) {
+  // Ensure that that kExpectedReturnValue + syscallnumber + 1 does not int
+  // overflow.
+  BPF_ASSERT(std::numeric_limits<int>::max() - kExpectedReturnValue - 1 >=
+             static_cast<int>(MAX_PUBLIC_SYSCALL));
+
+  for (int syscall_number = static_cast<int>(MIN_SYSCALL);
+       syscall_number <= static_cast<int>(MAX_PUBLIC_SYSCALL);
+       ++syscall_number) {
+    if (syscall_number == __NR_exit_group || syscall_number == __NR_write) {
+      // exit_group() is special
+      continue;
+    }
+    errno = 0;
+    BPF_ASSERT(syscall(syscall_number) == -1);
+    BPF_ASSERT(errno == SysnoToRandomErrno(syscall_number));
+  }
+}
+
+#if defined(__arm__)
+// A simple policy that tests whether ARM private system calls are supported
+// by our BPF compiler and by the BPF interpreter in the kernel.
+
+// For ARM private system calls, return an errno equal to their offset from
+// MIN_PRIVATE_SYSCALL plus 1 (to avoid NUL errno).
+int ArmPrivateSysnoToErrno(int sysno) {
+  if (sysno >= static_cast<int>(MIN_PRIVATE_SYSCALL) &&
+      sysno <= static_cast<int>(MAX_PRIVATE_SYSCALL)) {
+    return (sysno - MIN_PRIVATE_SYSCALL) + 1;
+  } else {
+    return ENOSYS;
+  }
+}
+
+class ArmPrivatePolicy : public SandboxBPFDSLPolicy {
+ public:
+  ArmPrivatePolicy() {}
+  virtual ~ArmPrivatePolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    // Start from |__ARM_NR_set_tls + 1| so as not to mess with actual
+    // ARM private system calls.
+    if (sysno >= static_cast<int>(__ARM_NR_set_tls + 1) &&
+        sysno <= static_cast<int>(MAX_PRIVATE_SYSCALL)) {
+      return Error(ArmPrivateSysnoToErrno(sysno));
+    }
+    return Allow();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ArmPrivatePolicy);
+};
+
+BPF_TEST_C(SandboxBPF, ArmPrivatePolicy, ArmPrivatePolicy) {
+  for (int syscall_number = static_cast<int>(__ARM_NR_set_tls + 1);
+       syscall_number <= static_cast<int>(MAX_PRIVATE_SYSCALL);
+       ++syscall_number) {
+    errno = 0;
+    BPF_ASSERT(syscall(syscall_number) == -1);
+    BPF_ASSERT(errno == ArmPrivateSysnoToErrno(syscall_number));
+  }
+}
+#endif  // defined(__arm__)
+
+intptr_t CountSyscalls(const struct arch_seccomp_data& args, void* aux) {
+  // Count all invocations of our callback function.
+  ++*reinterpret_cast<int*>(aux);
+
+  // Verify that within the callback function all filtering is temporarily
+  // disabled.
+  BPF_ASSERT(syscall(__NR_getpid) > 1);
+
+  // Verify that we can now call the underlying system call without causing
+  // infinite recursion.
+  return SandboxBPF::ForwardSyscall(args);
+}
+
+class GreyListedPolicy : public SandboxBPFDSLPolicy {
+ public:
+  explicit GreyListedPolicy(int* aux) : aux_(aux) {
+    // Set the global environment for unsafe traps once.
+    EnableUnsafeTraps();
+  }
+  virtual ~GreyListedPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    // Some system calls must always be allowed, if our policy wants to make
+    // use of UnsafeTrap()
+    if (SandboxBPF::IsRequiredForUnsafeTrap(sysno)) {
+      return Allow();
+    } else if (sysno == __NR_getpid) {
+      // Disallow getpid()
+      return Error(EPERM);
+    } else {
+      // Allow (and count) all other system calls.
+      return UnsafeTrap(CountSyscalls, aux_);
+    }
+  }
+
+ private:
+  int* aux_;
+
+  DISALLOW_COPY_AND_ASSIGN(GreyListedPolicy);
+};
+
+BPF_TEST(SandboxBPF, GreyListedPolicy, GreyListedPolicy, int /* (*BPF_AUX) */) {
+  BPF_ASSERT(syscall(__NR_getpid) == -1);
+  BPF_ASSERT(errno == EPERM);
+  BPF_ASSERT(*BPF_AUX == 0);
+  BPF_ASSERT(syscall(__NR_geteuid) == syscall(__NR_getuid));
+  BPF_ASSERT(*BPF_AUX == 2);
+  char name[17] = {};
+  BPF_ASSERT(!syscall(__NR_prctl,
+                      PR_GET_NAME,
+                      name,
+                      (void*)NULL,
+                      (void*)NULL,
+                      (void*)NULL));
+  BPF_ASSERT(*BPF_AUX == 3);
+  BPF_ASSERT(*name);
+}
+
+SANDBOX_TEST(SandboxBPF, EnableUnsafeTrapsInSigSysHandler) {
+  // Disabling warning messages that could confuse our test framework.
+  setenv(kSandboxDebuggingEnv, "t", 0);
+  Die::SuppressInfoMessages(true);
+
+  unsetenv(kSandboxDebuggingEnv);
+  SANDBOX_ASSERT(Trap::EnableUnsafeTrapsInSigSysHandler() == false);
+  setenv(kSandboxDebuggingEnv, "", 1);
+  SANDBOX_ASSERT(Trap::EnableUnsafeTrapsInSigSysHandler() == false);
+  setenv(kSandboxDebuggingEnv, "t", 1);
+  SANDBOX_ASSERT(Trap::EnableUnsafeTrapsInSigSysHandler() == true);
+}
+
+intptr_t PrctlHandler(const struct arch_seccomp_data& args, void*) {
+  if (args.args[0] == PR_CAPBSET_DROP && static_cast<int>(args.args[1]) == -1) {
+    // prctl(PR_CAPBSET_DROP, -1) is never valid. The kernel will always
+    // return an error. But our handler allows this call.
+    return 0;
+  } else {
+    return SandboxBPF::ForwardSyscall(args);
+  }
+}
+
+class PrctlPolicy : public SandboxBPFDSLPolicy {
+ public:
+  PrctlPolicy() {}
+  virtual ~PrctlPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    setenv(kSandboxDebuggingEnv, "t", 0);
+    Die::SuppressInfoMessages(true);
+
+    if (sysno == __NR_prctl) {
+      // Handle prctl() inside an UnsafeTrap()
+      return UnsafeTrap(PrctlHandler, NULL);
+    }
+
+    // Allow all other system calls.
+    return Allow();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PrctlPolicy);
+};
+
+BPF_TEST_C(SandboxBPF, ForwardSyscall, PrctlPolicy) {
+  // This call should never be allowed. But our policy will intercept it and
+  // let it pass successfully.
+  BPF_ASSERT(
+      !prctl(PR_CAPBSET_DROP, -1, (void*)NULL, (void*)NULL, (void*)NULL));
+
+  // Verify that the call will fail, if it makes it all the way to the kernel.
+  BPF_ASSERT(
+      prctl(PR_CAPBSET_DROP, -2, (void*)NULL, (void*)NULL, (void*)NULL) == -1);
+
+  // And verify that other uses of prctl() work just fine.
+  char name[17] = {};
+  BPF_ASSERT(!syscall(__NR_prctl,
+                      PR_GET_NAME,
+                      name,
+                      (void*)NULL,
+                      (void*)NULL,
+                      (void*)NULL));
+  BPF_ASSERT(*name);
+
+  // Finally, verify that system calls other than prctl() are completely
+  // unaffected by our policy.
+  struct utsname uts = {};
+  BPF_ASSERT(!uname(&uts));
+  BPF_ASSERT(!strcmp(uts.sysname, "Linux"));
+}
+
+intptr_t AllowRedirectedSyscall(const struct arch_seccomp_data& args, void*) {
+  return SandboxBPF::ForwardSyscall(args);
+}
+
+class RedirectAllSyscallsPolicy : public SandboxBPFDSLPolicy {
+ public:
+  RedirectAllSyscallsPolicy() {}
+  virtual ~RedirectAllSyscallsPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RedirectAllSyscallsPolicy);
+};
+
+ResultExpr RedirectAllSyscallsPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  setenv(kSandboxDebuggingEnv, "t", 0);
+  Die::SuppressInfoMessages(true);
+
+  // Some system calls must always be allowed, if our policy wants to make
+  // use of UnsafeTrap()
+  if (SandboxBPF::IsRequiredForUnsafeTrap(sysno))
+    return Allow();
+  return UnsafeTrap(AllowRedirectedSyscall, NULL);
+}
+
+int bus_handler_fd_ = -1;
+
+void SigBusHandler(int, siginfo_t* info, void* void_context) {
+  BPF_ASSERT(write(bus_handler_fd_, "\x55", 1) == 1);
+}
+
+BPF_TEST_C(SandboxBPF, SigBus, RedirectAllSyscallsPolicy) {
+  // We use the SIGBUS bit in the signal mask as a thread-local boolean
+  // value in the implementation of UnsafeTrap(). This is obviously a bit
+  // of a hack that could conceivably interfere with code that uses SIGBUS
+  // in more traditional ways. This test verifies that basic functionality
+  // of SIGBUS is not impacted, but it is certainly possibly to construe
+  // more complex uses of signals where our use of the SIGBUS mask is not
+  // 100% transparent. This is expected behavior.
+  int fds[2];
+  BPF_ASSERT(socketpair(AF_UNIX, SOCK_STREAM, 0, fds) == 0);
+  bus_handler_fd_ = fds[1];
+  struct sigaction sa = {};
+  sa.sa_sigaction = SigBusHandler;
+  sa.sa_flags = SA_SIGINFO;
+  BPF_ASSERT(sigaction(SIGBUS, &sa, NULL) == 0);
+  raise(SIGBUS);
+  char c = '\000';
+  BPF_ASSERT(read(fds[0], &c, 1) == 1);
+  BPF_ASSERT(close(fds[0]) == 0);
+  BPF_ASSERT(close(fds[1]) == 0);
+  BPF_ASSERT(c == 0x55);
+}
+
+BPF_TEST_C(SandboxBPF, SigMask, RedirectAllSyscallsPolicy) {
+  // Signal masks are potentially tricky to handle. For instance, if we
+  // ever tried to update them from inside a Trap() or UnsafeTrap() handler,
+  // the call to sigreturn() at the end of the signal handler would undo
+  // all of our efforts. So, it makes sense to test that sigprocmask()
+  // works, even if we have a policy in place that makes use of UnsafeTrap().
+  // In practice, this works because we force sigprocmask() to be handled
+  // entirely in the kernel.
+  sigset_t mask0, mask1, mask2;
+
+  // Call sigprocmask() to verify that SIGUSR2 wasn't blocked, if we didn't
+  // change the mask (it shouldn't have been, as it isn't blocked by default
+  // in POSIX).
+  //
+  // Use SIGUSR2 because Android seems to use SIGUSR1 for some purpose.
+  sigemptyset(&mask0);
+  BPF_ASSERT(!sigprocmask(SIG_BLOCK, &mask0, &mask1));
+  BPF_ASSERT(!sigismember(&mask1, SIGUSR2));
+
+  // Try again, and this time we verify that we can block it. This
+  // requires a second call to sigprocmask().
+  sigaddset(&mask0, SIGUSR2);
+  BPF_ASSERT(!sigprocmask(SIG_BLOCK, &mask0, NULL));
+  BPF_ASSERT(!sigprocmask(SIG_BLOCK, NULL, &mask2));
+  BPF_ASSERT(sigismember(&mask2, SIGUSR2));
+}
+
+BPF_TEST_C(SandboxBPF, UnsafeTrapWithErrno, RedirectAllSyscallsPolicy) {
+  // An UnsafeTrap() (or for that matter, a Trap()) has to report error
+  // conditions by returning an exit code in the range -1..-4096. This
+  // should happen automatically if using ForwardSyscall(). If the TrapFnc()
+  // uses some other method to make system calls, then it is responsible
+  // for computing the correct return code.
+  // This test verifies that ForwardSyscall() does the correct thing.
+
+  // The glibc system wrapper will ultimately set errno for us. So, from normal
+  // userspace, all of this should be completely transparent.
+  errno = 0;
+  BPF_ASSERT(close(-1) == -1);
+  BPF_ASSERT(errno == EBADF);
+
+  // Explicitly avoid the glibc wrapper. This is not normally the way anybody
+  // would make system calls, but it allows us to verify that we don't
+  // accidentally mess with errno, when we shouldn't.
+  errno = 0;
+  struct arch_seccomp_data args = {};
+  args.nr = __NR_close;
+  args.args[0] = -1;
+  BPF_ASSERT(SandboxBPF::ForwardSyscall(args) == -EBADF);
+  BPF_ASSERT(errno == 0);
+}
+
+bool NoOpCallback() {
+  return true;
+}
+
+// Test a trap handler that makes use of a broker process to open().
+
+class InitializedOpenBroker {
+ public:
+  InitializedOpenBroker() : initialized_(false) {
+    std::vector<std::string> allowed_files;
+    allowed_files.push_back("/proc/allowed");
+    allowed_files.push_back("/proc/cpuinfo");
+
+    broker_process_.reset(
+        new BrokerProcess(EPERM, allowed_files, std::vector<std::string>()));
+    BPF_ASSERT(broker_process() != NULL);
+    BPF_ASSERT(broker_process_->Init(base::Bind(&NoOpCallback)));
+
+    initialized_ = true;
+  }
+  bool initialized() { return initialized_; }
+  class BrokerProcess* broker_process() { return broker_process_.get(); }
+
+ private:
+  bool initialized_;
+  scoped_ptr<class BrokerProcess> broker_process_;
+  DISALLOW_COPY_AND_ASSIGN(InitializedOpenBroker);
+};
+
+intptr_t BrokerOpenTrapHandler(const struct arch_seccomp_data& args,
+                               void* aux) {
+  BPF_ASSERT(aux);
+  BrokerProcess* broker_process = static_cast<BrokerProcess*>(aux);
+  switch (args.nr) {
+    case __NR_faccessat:  // access is a wrapper of faccessat in android
+      BPF_ASSERT(static_cast<int>(args.args[0]) == AT_FDCWD);
+      return broker_process->Access(reinterpret_cast<const char*>(args.args[1]),
+                                    static_cast<int>(args.args[2]));
+#if defined(__NR_access)
+    case __NR_access:
+      return broker_process->Access(reinterpret_cast<const char*>(args.args[0]),
+                                    static_cast<int>(args.args[1]));
+#endif
+#if defined(__NR_open)
+    case __NR_open:
+      return broker_process->Open(reinterpret_cast<const char*>(args.args[0]),
+                                  static_cast<int>(args.args[1]));
+#endif
+    case __NR_openat:
+      // We only call open() so if we arrive here, it's because glibc uses
+      // the openat() system call.
+      BPF_ASSERT(static_cast<int>(args.args[0]) == AT_FDCWD);
+      return broker_process->Open(reinterpret_cast<const char*>(args.args[1]),
+                                  static_cast<int>(args.args[2]));
+    default:
+      BPF_ASSERT(false);
+      return -ENOSYS;
+  }
+}
+
+class DenyOpenPolicy : public SandboxBPFDSLPolicy {
+ public:
+  explicit DenyOpenPolicy(InitializedOpenBroker* iob) : iob_(iob) {}
+  virtual ~DenyOpenPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+
+    switch (sysno) {
+      case __NR_faccessat:
+#if defined(__NR_access)
+      case __NR_access:
+#endif
+#if defined(__NR_open)
+      case __NR_open:
+#endif
+      case __NR_openat:
+        // We get a InitializedOpenBroker class, but our trap handler wants
+        // the BrokerProcess object.
+        return Trap(BrokerOpenTrapHandler, iob_->broker_process());
+      default:
+        return Allow();
+    }
+  }
+
+ private:
+  InitializedOpenBroker* iob_;
+
+  DISALLOW_COPY_AND_ASSIGN(DenyOpenPolicy);
+};
+
+// We use a InitializedOpenBroker class, so that we can run unsandboxed
+// code in its constructor, which is the only way to do so in a BPF_TEST.
+BPF_TEST(SandboxBPF,
+         UseOpenBroker,
+         DenyOpenPolicy,
+         InitializedOpenBroker /* (*BPF_AUX) */) {
+  BPF_ASSERT(BPF_AUX->initialized());
+  BrokerProcess* broker_process = BPF_AUX->broker_process();
+  BPF_ASSERT(broker_process != NULL);
+
+  // First, use the broker "manually"
+  BPF_ASSERT(broker_process->Open("/proc/denied", O_RDONLY) == -EPERM);
+  BPF_ASSERT(broker_process->Access("/proc/denied", R_OK) == -EPERM);
+  BPF_ASSERT(broker_process->Open("/proc/allowed", O_RDONLY) == -ENOENT);
+  BPF_ASSERT(broker_process->Access("/proc/allowed", R_OK) == -ENOENT);
+
+  // Now use glibc's open() as an external library would.
+  BPF_ASSERT(open("/proc/denied", O_RDONLY) == -1);
+  BPF_ASSERT(errno == EPERM);
+
+  BPF_ASSERT(open("/proc/allowed", O_RDONLY) == -1);
+  BPF_ASSERT(errno == ENOENT);
+
+  // Also test glibc's openat(), some versions of libc use it transparently
+  // instead of open().
+  BPF_ASSERT(openat(AT_FDCWD, "/proc/denied", O_RDONLY) == -1);
+  BPF_ASSERT(errno == EPERM);
+
+  BPF_ASSERT(openat(AT_FDCWD, "/proc/allowed", O_RDONLY) == -1);
+  BPF_ASSERT(errno == ENOENT);
+
+  // And test glibc's access().
+  BPF_ASSERT(access("/proc/denied", R_OK) == -1);
+  BPF_ASSERT(errno == EPERM);
+
+  BPF_ASSERT(access("/proc/allowed", R_OK) == -1);
+  BPF_ASSERT(errno == ENOENT);
+
+  // This is also white listed and does exist.
+  int cpu_info_access = access("/proc/cpuinfo", R_OK);
+  BPF_ASSERT(cpu_info_access == 0);
+  int cpu_info_fd = open("/proc/cpuinfo", O_RDONLY);
+  BPF_ASSERT(cpu_info_fd >= 0);
+  char buf[1024];
+  BPF_ASSERT(read(cpu_info_fd, buf, sizeof(buf)) > 0);
+}
+
+// Simple test demonstrating how to use SandboxBPF::Cond()
+
+class SimpleCondTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  SimpleCondTestPolicy() {}
+  virtual ~SimpleCondTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SimpleCondTestPolicy);
+};
+
+ResultExpr SimpleCondTestPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+
+  // We deliberately return unusual errno values upon failure, so that we
+  // can uniquely test for these values. In a "real" policy, you would want
+  // to return more traditional values.
+  int flags_argument_position = -1;
+  switch (sysno) {
+#if defined(__NR_open)
+    case __NR_open:
+      flags_argument_position = 1;
+#endif
+    case __NR_openat: {  // open can be a wrapper for openat(2).
+      if (sysno == __NR_openat)
+        flags_argument_position = 2;
+
+      // Allow opening files for reading, but don't allow writing.
+      COMPILE_ASSERT(O_RDONLY == 0, O_RDONLY_must_be_all_zero_bits);
+      const Arg<int> flags(flags_argument_position);
+      return If((flags & O_ACCMODE) != 0, Error(EROFS)).Else(Allow());
+    }
+    case __NR_prctl: {
+      // Allow prctl(PR_SET_DUMPABLE) and prctl(PR_GET_DUMPABLE), but
+      // disallow everything else.
+      const Arg<int> option(0);
+      return If(option == PR_SET_DUMPABLE || option == PR_GET_DUMPABLE, Allow())
+          .Else(Error(ENOMEM));
+    }
+    default:
+      return Allow();
+  }
+}
+
+BPF_TEST_C(SandboxBPF, SimpleCondTest, SimpleCondTestPolicy) {
+  int fd;
+  BPF_ASSERT((fd = open("/proc/self/comm", O_RDWR)) == -1);
+  BPF_ASSERT(errno == EROFS);
+  BPF_ASSERT((fd = open("/proc/self/comm", O_RDONLY)) >= 0);
+  close(fd);
+
+  int ret;
+  BPF_ASSERT((ret = prctl(PR_GET_DUMPABLE)) >= 0);
+  BPF_ASSERT(prctl(PR_SET_DUMPABLE, 1 - ret) == 0);
+  BPF_ASSERT(prctl(PR_GET_ENDIAN, &ret) == -1);
+  BPF_ASSERT(errno == ENOMEM);
+}
+
+// This test exercises the SandboxBPF::Cond() method by building a complex
+// tree of conditional equality operations. It then makes system calls and
+// verifies that they return the values that we expected from our BPF
+// program.
+class EqualityStressTest {
+ public:
+  EqualityStressTest() {
+    // We want a deterministic test
+    srand(0);
+
+    // Iterates over system call numbers and builds a random tree of
+    // equality tests.
+    // We are actually constructing a graph of ArgValue objects. This
+    // graph will later be used to a) compute our sandbox policy, and
+    // b) drive the code that verifies the output from the BPF program.
+    COMPILE_ASSERT(
+        kNumTestCases < (int)(MAX_PUBLIC_SYSCALL - MIN_SYSCALL - 10),
+        num_test_cases_must_be_significantly_smaller_than_num_system_calls);
+    for (int sysno = MIN_SYSCALL, end = kNumTestCases; sysno < end; ++sysno) {
+      if (IsReservedSyscall(sysno)) {
+        // Skip reserved system calls. This ensures that our test frame
+        // work isn't impacted by the fact that we are overriding
+        // a lot of different system calls.
+        ++end;
+        arg_values_.push_back(NULL);
+      } else {
+        arg_values_.push_back(
+            RandomArgValue(rand() % kMaxArgs, 0, rand() % kMaxArgs));
+      }
+    }
+  }
+
+  ~EqualityStressTest() {
+    for (std::vector<ArgValue*>::iterator iter = arg_values_.begin();
+         iter != arg_values_.end();
+         ++iter) {
+      DeleteArgValue(*iter);
+    }
+  }
+
+  ResultExpr Policy(int sysno) {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    if (sysno < 0 || sysno >= (int)arg_values_.size() ||
+        IsReservedSyscall(sysno)) {
+      // We only return ErrorCode values for the system calls that
+      // are part of our test data. Every other system call remains
+      // allowed.
+      return Allow();
+    } else {
+      // ToErrorCode() turns an ArgValue object into an ErrorCode that is
+      // suitable for use by a sandbox policy.
+      return ToErrorCode(arg_values_[sysno]);
+    }
+  }
+
+  void VerifyFilter() {
+    // Iterate over all system calls. Skip the system calls that have
+    // previously been determined as being reserved.
+    for (int sysno = 0; sysno < (int)arg_values_.size(); ++sysno) {
+      if (!arg_values_[sysno]) {
+        // Skip reserved system calls.
+        continue;
+      }
+      // Verify that system calls return the values that we expect them to
+      // return. This involves passing different combinations of system call
+      // parameters in order to exercise all possible code paths through the
+      // BPF filter program.
+      // We arbitrarily start by setting all six system call arguments to
+      // zero. And we then recursive traverse our tree of ArgValues to
+      // determine the necessary combinations of parameters.
+      intptr_t args[6] = {};
+      Verify(sysno, args, *arg_values_[sysno]);
+    }
+  }
+
+ private:
+  struct ArgValue {
+    int argno;  // Argument number to inspect.
+    int size;   // Number of test cases (must be > 0).
+    struct Tests {
+      uint32_t k_value;            // Value to compare syscall arg against.
+      int err;                     // If non-zero, errno value to return.
+      struct ArgValue* arg_value;  // Otherwise, more args needs inspecting.
+    }* tests;
+    int err;                     // If none of the tests passed, this is what
+    struct ArgValue* arg_value;  // we'll return (this is the "else" branch).
+  };
+
+  bool IsReservedSyscall(int sysno) {
+    // There are a handful of system calls that we should never use in our
+    // test cases. These system calls are needed to allow the test framework
+    // to run properly.
+    // If we wanted to write fully generic code, there are more system calls
+    // that could be listed here, and it is quite difficult to come up with a
+    // truly comprehensive list. After all, we are deliberately making system
+    // calls unavailable. In practice, we have a pretty good idea of the system
+    // calls that will be made by this particular test. So, this small list is
+    // sufficient. But if anybody copy'n'pasted this code for other uses, they
+    // would have to review that the list.
+    return sysno == __NR_read || sysno == __NR_write || sysno == __NR_exit ||
+           sysno == __NR_exit_group || sysno == __NR_restart_syscall;
+  }
+
+  ArgValue* RandomArgValue(int argno, int args_mask, int remaining_args) {
+    // Create a new ArgValue and fill it with random data. We use as bit mask
+    // to keep track of the system call parameters that have previously been
+    // set; this ensures that we won't accidentally define a contradictory
+    // set of equality tests.
+    struct ArgValue* arg_value = new ArgValue();
+    args_mask |= 1 << argno;
+    arg_value->argno = argno;
+
+    // Apply some restrictions on just how complex our tests can be.
+    // Otherwise, we end up with a BPF program that is too complicated for
+    // the kernel to load.
+    int fan_out = kMaxFanOut;
+    if (remaining_args > 3) {
+      fan_out = 1;
+    } else if (remaining_args > 2) {
+      fan_out = 2;
+    }
+
+    // Create a couple of different test cases with randomized values that
+    // we want to use when comparing system call parameter number "argno".
+    arg_value->size = rand() % fan_out + 1;
+    arg_value->tests = new ArgValue::Tests[arg_value->size];
+
+    uint32_t k_value = rand();
+    for (int n = 0; n < arg_value->size; ++n) {
+      // Ensure that we have unique values
+      k_value += rand() % (RAND_MAX / (kMaxFanOut + 1)) + 1;
+
+      // There are two possible types of nodes. Either this is a leaf node;
+      // in that case, we have completed all the equality tests that we
+      // wanted to perform, and we can now compute a random "errno" value that
+      // we should return. Or this is part of a more complex boolean
+      // expression; in that case, we have to recursively add tests for some
+      // of system call parameters that we have not yet included in our
+      // tests.
+      arg_value->tests[n].k_value = k_value;
+      if (!remaining_args || (rand() & 1)) {
+        arg_value->tests[n].err = (rand() % 1000) + 1;
+        arg_value->tests[n].arg_value = NULL;
+      } else {
+        arg_value->tests[n].err = 0;
+        arg_value->tests[n].arg_value =
+            RandomArgValue(RandomArg(args_mask), args_mask, remaining_args - 1);
+      }
+    }
+    // Finally, we have to define what we should return if none of the
+    // previous equality tests pass. Again, we can either deal with a leaf
+    // node, or we can randomly add another couple of tests.
+    if (!remaining_args || (rand() & 1)) {
+      arg_value->err = (rand() % 1000) + 1;
+      arg_value->arg_value = NULL;
+    } else {
+      arg_value->err = 0;
+      arg_value->arg_value =
+          RandomArgValue(RandomArg(args_mask), args_mask, remaining_args - 1);
+    }
+    // We have now built a new (sub-)tree of ArgValues defining a set of
+    // boolean expressions for testing random system call arguments against
+    // random values. Return this tree to our caller.
+    return arg_value;
+  }
+
+  int RandomArg(int args_mask) {
+    // Compute a random system call parameter number.
+    int argno = rand() % kMaxArgs;
+
+    // Make sure that this same parameter number has not previously been
+    // used. Otherwise, we could end up with a test that is impossible to
+    // satisfy (e.g. args[0] == 1 && args[0] == 2).
+    while (args_mask & (1 << argno)) {
+      argno = (argno + 1) % kMaxArgs;
+    }
+    return argno;
+  }
+
+  void DeleteArgValue(ArgValue* arg_value) {
+    // Delete an ArgValue and all of its child nodes. This requires
+    // recursively descending into the tree.
+    if (arg_value) {
+      if (arg_value->size) {
+        for (int n = 0; n < arg_value->size; ++n) {
+          if (!arg_value->tests[n].err) {
+            DeleteArgValue(arg_value->tests[n].arg_value);
+          }
+        }
+        delete[] arg_value->tests;
+      }
+      if (!arg_value->err) {
+        DeleteArgValue(arg_value->arg_value);
+      }
+      delete arg_value;
+    }
+  }
+
+  ResultExpr ToErrorCode(ArgValue* arg_value) {
+    // Compute the ResultExpr that should be returned, if none of our
+    // tests succeed (i.e. the system call parameter doesn't match any
+    // of the values in arg_value->tests[].k_value).
+    ResultExpr err;
+    if (arg_value->err) {
+      // If this was a leaf node, return the errno value that we expect to
+      // return from the BPF filter program.
+      err = Error(arg_value->err);
+    } else {
+      // If this wasn't a leaf node yet, recursively descend into the rest
+      // of the tree. This will end up adding a few more SandboxBPF::Cond()
+      // tests to our ErrorCode.
+      err = ToErrorCode(arg_value->arg_value);
+    }
+
+    // Now, iterate over all the test cases that we want to compare against.
+    // This builds a chain of SandboxBPF::Cond() tests
+    // (aka "if ... elif ... elif ... elif ... fi")
+    for (int n = arg_value->size; n-- > 0;) {
+      ResultExpr matched;
+      // Again, we distinguish between leaf nodes and subtrees.
+      if (arg_value->tests[n].err) {
+        matched = Error(arg_value->tests[n].err);
+      } else {
+        matched = ToErrorCode(arg_value->tests[n].arg_value);
+      }
+      // For now, all of our tests are limited to 32bit.
+      // We have separate tests that check the behavior of 32bit vs. 64bit
+      // conditional expressions.
+      const Arg<uint32_t> arg(arg_value->argno);
+      err = If(arg == arg_value->tests[n].k_value, matched).Else(err);
+    }
+    return err;
+  }
+
+  void Verify(int sysno, intptr_t* args, const ArgValue& arg_value) {
+    uint32_t mismatched = 0;
+    // Iterate over all the k_values in arg_value.tests[] and verify that
+    // we see the expected return values from system calls, when we pass
+    // the k_value as a parameter in a system call.
+    for (int n = arg_value.size; n-- > 0;) {
+      mismatched += arg_value.tests[n].k_value;
+      args[arg_value.argno] = arg_value.tests[n].k_value;
+      if (arg_value.tests[n].err) {
+        VerifyErrno(sysno, args, arg_value.tests[n].err);
+      } else {
+        Verify(sysno, args, *arg_value.tests[n].arg_value);
+      }
+    }
+  // Find a k_value that doesn't match any of the k_values in
+  // arg_value.tests[]. In most cases, the current value of "mismatched"
+  // would fit this requirement. But on the off-chance that it happens
+  // to collide, we double-check.
+  try_again:
+    for (int n = arg_value.size; n-- > 0;) {
+      if (mismatched == arg_value.tests[n].k_value) {
+        ++mismatched;
+        goto try_again;
+      }
+    }
+    // Now verify that we see the expected return value from system calls,
+    // if we pass a value that doesn't match any of the conditions (i.e. this
+    // is testing the "else" clause of the conditions).
+    args[arg_value.argno] = mismatched;
+    if (arg_value.err) {
+      VerifyErrno(sysno, args, arg_value.err);
+    } else {
+      Verify(sysno, args, *arg_value.arg_value);
+    }
+    // Reset args[arg_value.argno]. This is not technically needed, but it
+    // makes it easier to reason about the correctness of our tests.
+    args[arg_value.argno] = 0;
+  }
+
+  void VerifyErrno(int sysno, intptr_t* args, int err) {
+    // We installed BPF filters that return different errno values
+    // based on the system call number and the parameters that we decided
+    // to pass in. Verify that this condition holds true.
+    BPF_ASSERT(
+        Syscall::Call(
+            sysno, args[0], args[1], args[2], args[3], args[4], args[5]) ==
+        -err);
+  }
+
+  // Vector of ArgValue trees. These trees define all the possible boolean
+  // expressions that we want to turn into a BPF filter program.
+  std::vector<ArgValue*> arg_values_;
+
+  // Don't increase these values. We are pushing the limits of the maximum
+  // BPF program that the kernel will allow us to load. If the values are
+  // increased too much, the test will start failing.
+#if defined(__aarch64__)
+  static const int kNumTestCases = 30;
+#else
+  static const int kNumTestCases = 40;
+#endif
+  static const int kMaxFanOut = 3;
+  static const int kMaxArgs = 6;
+};
+
+class EqualityStressTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  explicit EqualityStressTestPolicy(EqualityStressTest* aux) : aux_(aux) {}
+  virtual ~EqualityStressTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    return aux_->Policy(sysno);
+  }
+
+ private:
+  EqualityStressTest* aux_;
+
+  DISALLOW_COPY_AND_ASSIGN(EqualityStressTestPolicy);
+};
+
+BPF_TEST(SandboxBPF,
+         EqualityTests,
+         EqualityStressTestPolicy,
+         EqualityStressTest /* (*BPF_AUX) */) {
+  BPF_AUX->VerifyFilter();
+}
+
+class EqualityArgumentWidthPolicy : public SandboxBPFDSLPolicy {
+ public:
+  EqualityArgumentWidthPolicy() {}
+  virtual ~EqualityArgumentWidthPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(EqualityArgumentWidthPolicy);
+};
+
+ResultExpr EqualityArgumentWidthPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  if (sysno == __NR_uname) {
+    const Arg<int> option(0);
+    const Arg<uint32_t> arg32(1);
+    const Arg<uint64_t> arg64(1);
+    return Switch(option)
+        .Case(0, If(arg32 == 0x55555555, Error(1)).Else(Error(2)))
+#if __SIZEOF_POINTER__ > 4
+        .Case(1, If(arg64 == 0x55555555AAAAAAAAULL, Error(1)).Else(Error(2)))
+#endif
+        .Default(Error(3));
+  }
+  return Allow();
+}
+
+BPF_TEST_C(SandboxBPF, EqualityArgumentWidth, EqualityArgumentWidthPolicy) {
+  BPF_ASSERT(Syscall::Call(__NR_uname, 0, 0x55555555) == -1);
+  BPF_ASSERT(Syscall::Call(__NR_uname, 0, 0xAAAAAAAA) == -2);
+#if __SIZEOF_POINTER__ > 4
+  // On 32bit machines, there is no way to pass a 64bit argument through the
+  // syscall interface. So, we have to skip the part of the test that requires
+  // 64bit arguments.
+  BPF_ASSERT(Syscall::Call(__NR_uname, 1, 0x55555555AAAAAAAAULL) == -1);
+  BPF_ASSERT(Syscall::Call(__NR_uname, 1, 0x5555555500000000ULL) == -2);
+  BPF_ASSERT(Syscall::Call(__NR_uname, 1, 0x5555555511111111ULL) == -2);
+  BPF_ASSERT(Syscall::Call(__NR_uname, 1, 0x11111111AAAAAAAAULL) == -2);
+#endif
+}
+
+#if __SIZEOF_POINTER__ > 4
+// On 32bit machines, there is no way to pass a 64bit argument through the
+// syscall interface. So, we have to skip the part of the test that requires
+// 64bit arguments.
+BPF_DEATH_TEST_C(SandboxBPF,
+                 EqualityArgumentUnallowed64bit,
+                 DEATH_MESSAGE("Unexpected 64bit argument detected"),
+                 EqualityArgumentWidthPolicy) {
+  Syscall::Call(__NR_uname, 0, 0x5555555555555555ULL);
+}
+#endif
+
+class EqualityWithNegativeArgumentsPolicy : public SandboxBPFDSLPolicy {
+ public:
+  EqualityWithNegativeArgumentsPolicy() {}
+  virtual ~EqualityWithNegativeArgumentsPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    if (sysno == __NR_uname) {
+      // TODO(mdempsky): This currently can't be Arg<int> because then
+      // 0xFFFFFFFF will be treated as a (signed) int, and then when
+      // Arg::EqualTo casts it to uint64_t, it will be sign extended.
+      const Arg<unsigned> arg(0);
+      return If(arg == 0xFFFFFFFF, Error(1)).Else(Error(2));
+    }
+    return Allow();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(EqualityWithNegativeArgumentsPolicy);
+};
+
+BPF_TEST_C(SandboxBPF,
+           EqualityWithNegativeArguments,
+           EqualityWithNegativeArgumentsPolicy) {
+  BPF_ASSERT(Syscall::Call(__NR_uname, 0xFFFFFFFF) == -1);
+  BPF_ASSERT(Syscall::Call(__NR_uname, -1) == -1);
+  BPF_ASSERT(Syscall::Call(__NR_uname, -1LL) == -1);
+}
+
+#if __SIZEOF_POINTER__ > 4
+BPF_DEATH_TEST_C(SandboxBPF,
+                 EqualityWithNegative64bitArguments,
+                 DEATH_MESSAGE("Unexpected 64bit argument detected"),
+                 EqualityWithNegativeArgumentsPolicy) {
+  // When expecting a 32bit system call argument, we look at the MSB of the
+  // 64bit value and allow both "0" and "-1". But the latter is allowed only
+  // iff the LSB was negative. So, this death test should error out.
+  BPF_ASSERT(Syscall::Call(__NR_uname, 0xFFFFFFFF00000000LL) == -1);
+}
+#endif
+
+class AllBitTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  AllBitTestPolicy() {}
+  virtual ~AllBitTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  static ResultExpr HasAllBits32(uint32_t bits);
+  static ResultExpr HasAllBits64(uint64_t bits);
+
+  DISALLOW_COPY_AND_ASSIGN(AllBitTestPolicy);
+};
+
+ResultExpr AllBitTestPolicy::HasAllBits32(uint32_t bits) {
+  if (bits == 0) {
+    return Error(1);
+  }
+  const Arg<uint32_t> arg(1);
+  return If((arg & bits) == bits, Error(1)).Else(Error(0));
+}
+
+ResultExpr AllBitTestPolicy::HasAllBits64(uint64_t bits) {
+  if (bits == 0) {
+    return Error(1);
+  }
+  const Arg<uint64_t> arg(1);
+  return If((arg & bits) == bits, Error(1)).Else(Error(0));
+}
+
+ResultExpr AllBitTestPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  // Test masked-equality cases that should trigger the "has all bits"
+  // peephole optimizations. We try to find bitmasks that could conceivably
+  // touch corner cases.
+  // For all of these tests, we override the uname(). We can make use with
+  // a single system call number, as we use the first system call argument to
+  // select the different bit masks that we want to test against.
+  if (sysno == __NR_uname) {
+    const Arg<int> option(0);
+    return Switch(option)
+        .Case(0, HasAllBits32(0x0))
+        .Case(1, HasAllBits32(0x1))
+        .Case(2, HasAllBits32(0x3))
+        .Case(3, HasAllBits32(0x80000000))
+#if __SIZEOF_POINTER__ > 4
+        .Case(4, HasAllBits64(0x0))
+        .Case(5, HasAllBits64(0x1))
+        .Case(6, HasAllBits64(0x3))
+        .Case(7, HasAllBits64(0x80000000))
+        .Case(8, HasAllBits64(0x100000000ULL))
+        .Case(9, HasAllBits64(0x300000000ULL))
+        .Case(10, HasAllBits64(0x100000001ULL))
+#endif
+        .Default(Kill("Invalid test case number"));
+  }
+  return Allow();
+}
+
+// Define a macro that performs tests using our test policy.
+// NOTE: Not all of the arguments in this macro are actually used!
+//       They are here just to serve as documentation of the conditions
+//       implemented in the test policy.
+//       Most notably, "op" and "mask" are unused by the macro. If you want
+//       to make changes to these values, you will have to edit the
+//       test policy instead.
+#define BITMASK_TEST(testcase, arg, op, mask, expected_value) \
+  BPF_ASSERT(Syscall::Call(__NR_uname, (testcase), (arg)) == (expected_value))
+
+// Our uname() system call returns ErrorCode(1) for success and
+// ErrorCode(0) for failure. Syscall::Call() turns this into an
+// exit code of -1 or 0.
+#define EXPECT_FAILURE 0
+#define EXPECT_SUCCESS -1
+
+// A couple of our tests behave differently on 32bit and 64bit systems, as
+// there is no way for a 32bit system call to pass in a 64bit system call
+// argument "arg".
+// We expect these tests to succeed on 64bit systems, but to tail on 32bit
+// systems.
+#define EXPT64_SUCCESS (sizeof(void*) > 4 ? EXPECT_SUCCESS : EXPECT_FAILURE)
+BPF_TEST_C(SandboxBPF, AllBitTests, AllBitTestPolicy) {
+  // 32bit test: all of 0x0 (should always be true)
+  BITMASK_TEST( 0,                   0, ALLBITS32,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 0,                   1, ALLBITS32,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 0,                   3, ALLBITS32,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 0,         0xFFFFFFFFU, ALLBITS32,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 0,                -1LL, ALLBITS32,          0, EXPECT_SUCCESS);
+
+  // 32bit test: all of 0x1
+  BITMASK_TEST( 1,                   0, ALLBITS32,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 1,                   1, ALLBITS32,        0x1, EXPECT_SUCCESS);
+  BITMASK_TEST( 1,                   2, ALLBITS32,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 1,                   3, ALLBITS32,        0x1, EXPECT_SUCCESS);
+
+  // 32bit test: all of 0x3
+  BITMASK_TEST( 2,                   0, ALLBITS32,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 2,                   1, ALLBITS32,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 2,                   2, ALLBITS32,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 2,                   3, ALLBITS32,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 2,                   7, ALLBITS32,        0x3, EXPECT_SUCCESS);
+
+  // 32bit test: all of 0x80000000
+  BITMASK_TEST( 3,                   0, ALLBITS32, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 3,         0x40000000U, ALLBITS32, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 3,         0x80000000U, ALLBITS32, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 3,         0xC0000000U, ALLBITS32, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 3,       -0x80000000LL, ALLBITS32, 0x80000000, EXPECT_SUCCESS);
+
+#if __SIZEOF_POINTER__ > 4
+  // 64bit test: all of 0x0 (should always be true)
+  BITMASK_TEST( 4,                   0, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,                   1, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,                   3, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,         0xFFFFFFFFU, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,       0x100000000LL, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,       0x300000000LL, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,0x8000000000000000LL, ALLBITS64,          0, EXPECT_SUCCESS);
+  BITMASK_TEST( 4,                -1LL, ALLBITS64,          0, EXPECT_SUCCESS);
+
+  // 64bit test: all of 0x1
+  BITMASK_TEST( 5,                   0, ALLBITS64,          1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,                   1, ALLBITS64,          1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,                   2, ALLBITS64,          1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,                   3, ALLBITS64,          1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,       0x100000000LL, ALLBITS64,          1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,       0x100000001LL, ALLBITS64,          1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,       0x100000002LL, ALLBITS64,          1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,       0x100000003LL, ALLBITS64,          1, EXPECT_SUCCESS);
+
+  // 64bit test: all of 0x3
+  BITMASK_TEST( 6,                   0, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,                   1, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,                   2, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,                   3, ALLBITS64,          3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,                   7, ALLBITS64,          3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000000LL, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,       0x100000001LL, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,       0x100000002LL, ALLBITS64,          3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,       0x100000003LL, ALLBITS64,          3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000007LL, ALLBITS64,          3, EXPECT_SUCCESS);
+
+  // 64bit test: all of 0x80000000
+  BITMASK_TEST( 7,                   0, ALLBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,         0x40000000U, ALLBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,         0x80000000U, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,         0xC0000000U, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       -0x80000000LL, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       0x100000000LL, ALLBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,       0x140000000LL, ALLBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,       0x180000000LL, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       0x1C0000000LL, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,      -0x180000000LL, ALLBITS64, 0x80000000, EXPECT_SUCCESS);
+
+  // 64bit test: all of 0x100000000
+  BITMASK_TEST( 8,       0x000000000LL, ALLBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x100000000LL, ALLBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x200000000LL, ALLBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x300000000LL, ALLBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x000000001LL, ALLBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x100000001LL, ALLBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x200000001LL, ALLBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x300000001LL, ALLBITS64,0x100000000, EXPT64_SUCCESS);
+
+  // 64bit test: all of 0x300000000
+  BITMASK_TEST( 9,       0x000000000LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x100000000LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x200000000LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x300000000LL, ALLBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x700000000LL, ALLBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x000000001LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x100000001LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x200000001LL, ALLBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x300000001LL, ALLBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x700000001LL, ALLBITS64,0x300000000, EXPT64_SUCCESS);
+
+  // 64bit test: all of 0x100000001
+  BITMASK_TEST(10,       0x000000000LL, ALLBITS64,0x100000001, EXPECT_FAILURE);
+  BITMASK_TEST(10,       0x000000001LL, ALLBITS64,0x100000001, EXPECT_FAILURE);
+  BITMASK_TEST(10,       0x100000000LL, ALLBITS64,0x100000001, EXPECT_FAILURE);
+  BITMASK_TEST(10,       0x100000001LL, ALLBITS64,0x100000001, EXPT64_SUCCESS);
+  BITMASK_TEST(10,         0xFFFFFFFFU, ALLBITS64,0x100000001, EXPECT_FAILURE);
+  BITMASK_TEST(10,                 -1L, ALLBITS64,0x100000001, EXPT64_SUCCESS);
+#endif
+}
+
+class AnyBitTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  AnyBitTestPolicy() {}
+  virtual ~AnyBitTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  static ResultExpr HasAnyBits32(uint32_t);
+  static ResultExpr HasAnyBits64(uint64_t);
+
+  DISALLOW_COPY_AND_ASSIGN(AnyBitTestPolicy);
+};
+
+ResultExpr AnyBitTestPolicy::HasAnyBits32(uint32_t bits) {
+  if (bits == 0) {
+    return Error(0);
+  }
+  const Arg<uint32_t> arg(1);
+  return If((arg & bits) != 0, Error(1)).Else(Error(0));
+}
+
+ResultExpr AnyBitTestPolicy::HasAnyBits64(uint64_t bits) {
+  if (bits == 0) {
+    return Error(0);
+  }
+  const Arg<uint64_t> arg(1);
+  return If((arg & bits) != 0, Error(1)).Else(Error(0));
+}
+
+ResultExpr AnyBitTestPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  // Test masked-equality cases that should trigger the "has any bits"
+  // peephole optimizations. We try to find bitmasks that could conceivably
+  // touch corner cases.
+  // For all of these tests, we override the uname(). We can make use with
+  // a single system call number, as we use the first system call argument to
+  // select the different bit masks that we want to test against.
+  if (sysno == __NR_uname) {
+    const Arg<int> option(0);
+    return Switch(option)
+        .Case(0, HasAnyBits32(0x0))
+        .Case(1, HasAnyBits32(0x1))
+        .Case(2, HasAnyBits32(0x3))
+        .Case(3, HasAnyBits32(0x80000000))
+#if __SIZEOF_POINTER__ > 4
+        .Case(4, HasAnyBits64(0x0))
+        .Case(5, HasAnyBits64(0x1))
+        .Case(6, HasAnyBits64(0x3))
+        .Case(7, HasAnyBits64(0x80000000))
+        .Case(8, HasAnyBits64(0x100000000ULL))
+        .Case(9, HasAnyBits64(0x300000000ULL))
+        .Case(10, HasAnyBits64(0x100000001ULL))
+#endif
+        .Default(Kill("Invalid test case number"));
+  }
+  return Allow();
+}
+
+BPF_TEST_C(SandboxBPF, AnyBitTests, AnyBitTestPolicy) {
+  // 32bit test: any of 0x0 (should always be false)
+  BITMASK_TEST( 0,                   0, ANYBITS32,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 0,                   1, ANYBITS32,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 0,                   3, ANYBITS32,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 0,         0xFFFFFFFFU, ANYBITS32,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 0,                -1LL, ANYBITS32,        0x0, EXPECT_FAILURE);
+
+  // 32bit test: any of 0x1
+  BITMASK_TEST( 1,                   0, ANYBITS32,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 1,                   1, ANYBITS32,        0x1, EXPECT_SUCCESS);
+  BITMASK_TEST( 1,                   2, ANYBITS32,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 1,                   3, ANYBITS32,        0x1, EXPECT_SUCCESS);
+
+  // 32bit test: any of 0x3
+  BITMASK_TEST( 2,                   0, ANYBITS32,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 2,                   1, ANYBITS32,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 2,                   2, ANYBITS32,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 2,                   3, ANYBITS32,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 2,                   7, ANYBITS32,        0x3, EXPECT_SUCCESS);
+
+  // 32bit test: any of 0x80000000
+  BITMASK_TEST( 3,                   0, ANYBITS32, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 3,         0x40000000U, ANYBITS32, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 3,         0x80000000U, ANYBITS32, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 3,         0xC0000000U, ANYBITS32, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 3,       -0x80000000LL, ANYBITS32, 0x80000000, EXPECT_SUCCESS);
+
+#if __SIZEOF_POINTER__ > 4
+  // 64bit test: any of 0x0 (should always be false)
+  BITMASK_TEST( 4,                   0, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,                   1, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,                   3, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,         0xFFFFFFFFU, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,       0x100000000LL, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,       0x300000000LL, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,0x8000000000000000LL, ANYBITS64,        0x0, EXPECT_FAILURE);
+  BITMASK_TEST( 4,                -1LL, ANYBITS64,        0x0, EXPECT_FAILURE);
+
+  // 64bit test: any of 0x1
+  BITMASK_TEST( 5,                   0, ANYBITS64,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,                   1, ANYBITS64,        0x1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,                   2, ANYBITS64,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,                   3, ANYBITS64,        0x1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,       0x100000001LL, ANYBITS64,        0x1, EXPECT_SUCCESS);
+  BITMASK_TEST( 5,       0x100000000LL, ANYBITS64,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,       0x100000002LL, ANYBITS64,        0x1, EXPECT_FAILURE);
+  BITMASK_TEST( 5,       0x100000003LL, ANYBITS64,        0x1, EXPECT_SUCCESS);
+
+  // 64bit test: any of 0x3
+  BITMASK_TEST( 6,                   0, ANYBITS64,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,                   1, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,                   2, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,                   3, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,                   7, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000000LL, ANYBITS64,        0x3, EXPECT_FAILURE);
+  BITMASK_TEST( 6,       0x100000001LL, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000002LL, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000003LL, ANYBITS64,        0x3, EXPECT_SUCCESS);
+  BITMASK_TEST( 6,       0x100000007LL, ANYBITS64,        0x3, EXPECT_SUCCESS);
+
+  // 64bit test: any of 0x80000000
+  BITMASK_TEST( 7,                   0, ANYBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,         0x40000000U, ANYBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,         0x80000000U, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,         0xC0000000U, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       -0x80000000LL, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       0x100000000LL, ANYBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,       0x140000000LL, ANYBITS64, 0x80000000, EXPECT_FAILURE);
+  BITMASK_TEST( 7,       0x180000000LL, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,       0x1C0000000LL, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+  BITMASK_TEST( 7,      -0x180000000LL, ANYBITS64, 0x80000000, EXPECT_SUCCESS);
+
+  // 64bit test: any of 0x100000000
+  BITMASK_TEST( 8,       0x000000000LL, ANYBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x100000000LL, ANYBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x200000000LL, ANYBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x300000000LL, ANYBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x000000001LL, ANYBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x100000001LL, ANYBITS64,0x100000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 8,       0x200000001LL, ANYBITS64,0x100000000, EXPECT_FAILURE);
+  BITMASK_TEST( 8,       0x300000001LL, ANYBITS64,0x100000000, EXPT64_SUCCESS);
+
+  // 64bit test: any of 0x300000000
+  BITMASK_TEST( 9,       0x000000000LL, ANYBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x100000000LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x200000000LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x300000000LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x700000000LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x000000001LL, ANYBITS64,0x300000000, EXPECT_FAILURE);
+  BITMASK_TEST( 9,       0x100000001LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x200000001LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x300000001LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+  BITMASK_TEST( 9,       0x700000001LL, ANYBITS64,0x300000000, EXPT64_SUCCESS);
+
+  // 64bit test: any of 0x100000001
+  BITMASK_TEST( 10,      0x000000000LL, ANYBITS64,0x100000001, EXPECT_FAILURE);
+  BITMASK_TEST( 10,      0x000000001LL, ANYBITS64,0x100000001, EXPECT_SUCCESS);
+  BITMASK_TEST( 10,      0x100000000LL, ANYBITS64,0x100000001, EXPT64_SUCCESS);
+  BITMASK_TEST( 10,      0x100000001LL, ANYBITS64,0x100000001, EXPECT_SUCCESS);
+  BITMASK_TEST( 10,        0xFFFFFFFFU, ANYBITS64,0x100000001, EXPECT_SUCCESS);
+  BITMASK_TEST( 10,                -1L, ANYBITS64,0x100000001, EXPECT_SUCCESS);
+#endif
+}
+
+class MaskedEqualTestPolicy : public SandboxBPFDSLPolicy {
+ public:
+  MaskedEqualTestPolicy() {}
+  virtual ~MaskedEqualTestPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  static ResultExpr MaskedEqual32(uint32_t mask, uint32_t value);
+  static ResultExpr MaskedEqual64(uint64_t mask, uint64_t value);
+
+  DISALLOW_COPY_AND_ASSIGN(MaskedEqualTestPolicy);
+};
+
+ResultExpr MaskedEqualTestPolicy::MaskedEqual32(uint32_t mask, uint32_t value) {
+  const Arg<uint32_t> arg(1);
+  return If((arg & mask) == value, Error(1)).Else(Error(0));
+}
+
+ResultExpr MaskedEqualTestPolicy::MaskedEqual64(uint64_t mask, uint64_t value) {
+  const Arg<uint64_t> arg(1);
+  return If((arg & mask) == value, Error(1)).Else(Error(0));
+}
+
+ResultExpr MaskedEqualTestPolicy::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+
+  if (sysno == __NR_uname) {
+    const Arg<int> option(0);
+    return Switch(option)
+        .Case(0, MaskedEqual32(0x00ff00ff, 0x005500aa))
+#if __SIZEOF_POINTER__ > 4
+        .Case(1, MaskedEqual64(0x00ff00ff00000000, 0x005500aa00000000))
+        .Case(2, MaskedEqual64(0x00ff00ff00ff00ff, 0x005500aa005500aa))
+#endif
+        .Default(Kill("Invalid test case number"));
+  }
+
+  return Allow();
+}
+
+#define MASKEQ_TEST(rulenum, arg, expected_result) \
+  BPF_ASSERT(Syscall::Call(__NR_uname, (rulenum), (arg)) == (expected_result))
+
+BPF_TEST_C(SandboxBPF, MaskedEqualTests, MaskedEqualTestPolicy) {
+  // Allowed:    0x__55__aa
+  MASKEQ_TEST(0, 0x00000000, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x00000001, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x00000003, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x00000100, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x00000300, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x005500aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(0, 0x005500ab, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x005600aa, EXPECT_FAILURE);
+  MASKEQ_TEST(0, 0x005501aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(0, 0x005503aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(0, 0x555500aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(0, 0xaa5500aa, EXPECT_SUCCESS);
+
+#if __SIZEOF_POINTER__ > 4
+  // Allowed:    0x__55__aa________
+  MASKEQ_TEST(1, 0x0000000000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000000000000010, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000000000000050, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000000100000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000000300000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000010000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x0000030000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x005500aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0x005500ab00000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x005600aa00000000, EXPECT_FAILURE);
+  MASKEQ_TEST(1, 0x005501aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0x005503aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0x555500aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0xaa5500aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0xaa5500aa00000000, EXPECT_SUCCESS);
+  MASKEQ_TEST(1, 0xaa5500aa0000cafe, EXPECT_SUCCESS);
+
+  // Allowed:    0x__55__aa__55__aa
+  MASKEQ_TEST(2, 0x0000000000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000000000000010, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000000000000050, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000000100000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000000300000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000010000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x0000030000000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x00000000005500aa, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x005500aa00000000, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x005500aa005500aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(2, 0x005500aa005700aa, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x005700aa005500aa, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x005500aa004500aa, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x004500aa005500aa, EXPECT_FAILURE);
+  MASKEQ_TEST(2, 0x005512aa005500aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(2, 0x005500aa005534aa, EXPECT_SUCCESS);
+  MASKEQ_TEST(2, 0xff5500aa0055ffaa, EXPECT_SUCCESS);
+#endif
+}
+
+intptr_t PthreadTrapHandler(const struct arch_seccomp_data& args, void* aux) {
+  if (args.args[0] != (CLONE_CHILD_CLEARTID | CLONE_CHILD_SETTID | SIGCHLD)) {
+    // We expect to get called for an attempt to fork(). No need to log that
+    // call. But if we ever get called for anything else, we want to verbosely
+    // print as much information as possible.
+    const char* msg = (const char*)aux;
+    printf(
+        "Clone() was called with unexpected arguments\n"
+        "  nr: %d\n"
+        "  1: 0x%llX\n"
+        "  2: 0x%llX\n"
+        "  3: 0x%llX\n"
+        "  4: 0x%llX\n"
+        "  5: 0x%llX\n"
+        "  6: 0x%llX\n"
+        "%s\n",
+        args.nr,
+        (long long)args.args[0],
+        (long long)args.args[1],
+        (long long)args.args[2],
+        (long long)args.args[3],
+        (long long)args.args[4],
+        (long long)args.args[5],
+        msg);
+  }
+  return -EPERM;
+}
+
+class PthreadPolicyEquality : public SandboxBPFDSLPolicy {
+ public:
+  PthreadPolicyEquality() {}
+  virtual ~PthreadPolicyEquality() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PthreadPolicyEquality);
+};
+
+ResultExpr PthreadPolicyEquality::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  // This policy allows creating threads with pthread_create(). But it
+  // doesn't allow any other uses of clone(). Most notably, it does not
+  // allow callers to implement fork() or vfork() by passing suitable flags
+  // to the clone() system call.
+  if (sysno == __NR_clone) {
+    // We have seen two different valid combinations of flags. Glibc
+    // uses the more modern flags, sets the TLS from the call to clone(), and
+    // uses futexes to monitor threads. Android's C run-time library, doesn't
+    // do any of this, but it sets the obsolete (and no-op) CLONE_DETACHED.
+    // More recent versions of Android don't set CLONE_DETACHED anymore, so
+    // the last case accounts for that.
+    // The following policy is very strict. It only allows the exact masks
+    // that we have seen in known implementations. It is probably somewhat
+    // stricter than what we would want to do.
+    const uint64_t kGlibcCloneMask = CLONE_VM | CLONE_FS | CLONE_FILES |
+                                     CLONE_SIGHAND | CLONE_THREAD |
+                                     CLONE_SYSVSEM | CLONE_SETTLS |
+                                     CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID;
+    const uint64_t kBaseAndroidCloneMask = CLONE_VM | CLONE_FS | CLONE_FILES |
+                                           CLONE_SIGHAND | CLONE_THREAD |
+                                           CLONE_SYSVSEM;
+    const Arg<unsigned long> flags(0);
+    return If(flags == kGlibcCloneMask ||
+                  flags == (kBaseAndroidCloneMask | CLONE_DETACHED) ||
+                  flags == kBaseAndroidCloneMask,
+              Allow()).Else(Trap(PthreadTrapHandler, "Unknown mask"));
+  }
+
+  return Allow();
+}
+
+class PthreadPolicyBitMask : public SandboxBPFDSLPolicy {
+ public:
+  PthreadPolicyBitMask() {}
+  virtual ~PthreadPolicyBitMask() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override;
+
+ private:
+  static BoolExpr HasAnyBits(const Arg<unsigned long>& arg, unsigned long bits);
+  static BoolExpr HasAllBits(const Arg<unsigned long>& arg, unsigned long bits);
+
+  DISALLOW_COPY_AND_ASSIGN(PthreadPolicyBitMask);
+};
+
+BoolExpr PthreadPolicyBitMask::HasAnyBits(const Arg<unsigned long>& arg,
+                                          unsigned long bits) {
+  return (arg & bits) != 0;
+}
+
+BoolExpr PthreadPolicyBitMask::HasAllBits(const Arg<unsigned long>& arg,
+                                          unsigned long bits) {
+  return (arg & bits) == bits;
+}
+
+ResultExpr PthreadPolicyBitMask::EvaluateSyscall(int sysno) const {
+  DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+  // This policy allows creating threads with pthread_create(). But it
+  // doesn't allow any other uses of clone(). Most notably, it does not
+  // allow callers to implement fork() or vfork() by passing suitable flags
+  // to the clone() system call.
+  if (sysno == __NR_clone) {
+    // We have seen two different valid combinations of flags. Glibc
+    // uses the more modern flags, sets the TLS from the call to clone(), and
+    // uses futexes to monitor threads. Android's C run-time library, doesn't
+    // do any of this, but it sets the obsolete (and no-op) CLONE_DETACHED.
+    // The following policy allows for either combination of flags, but it
+    // is generally a little more conservative than strictly necessary. We
+    // err on the side of rather safe than sorry.
+    // Very noticeably though, we disallow fork() (which is often just a
+    // wrapper around clone()).
+    const unsigned long kMandatoryFlags = CLONE_VM | CLONE_FS | CLONE_FILES |
+                                          CLONE_SIGHAND | CLONE_THREAD |
+                                          CLONE_SYSVSEM;
+    const unsigned long kFutexFlags =
+        CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID;
+    const unsigned long kNoopFlags = CLONE_DETACHED;
+    const unsigned long kKnownFlags =
+        kMandatoryFlags | kFutexFlags | kNoopFlags;
+
+    const Arg<unsigned long> flags(0);
+    return If(HasAnyBits(flags, ~kKnownFlags),
+              Trap(PthreadTrapHandler, "Unexpected CLONE_XXX flag found"))
+        .ElseIf(!HasAllBits(flags, kMandatoryFlags),
+                Trap(PthreadTrapHandler,
+                     "Missing mandatory CLONE_XXX flags "
+                     "when creating new thread"))
+        .ElseIf(
+             !HasAllBits(flags, kFutexFlags) && HasAnyBits(flags, kFutexFlags),
+             Trap(PthreadTrapHandler,
+                  "Must set either all or none of the TLS and futex bits in "
+                  "call to clone()"))
+        .Else(Allow());
+  }
+
+  return Allow();
+}
+
+static void* ThreadFnc(void* arg) {
+  ++*reinterpret_cast<int*>(arg);
+  Syscall::Call(__NR_futex, arg, FUTEX_WAKE, 1, 0, 0, 0);
+  return NULL;
+}
+
+static void PthreadTest() {
+  // Attempt to start a joinable thread. This should succeed.
+  pthread_t thread;
+  int thread_ran = 0;
+  BPF_ASSERT(!pthread_create(&thread, NULL, ThreadFnc, &thread_ran));
+  BPF_ASSERT(!pthread_join(thread, NULL));
+  BPF_ASSERT(thread_ran);
+
+  // Attempt to start a detached thread. This should succeed.
+  thread_ran = 0;
+  pthread_attr_t attr;
+  BPF_ASSERT(!pthread_attr_init(&attr));
+  BPF_ASSERT(!pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED));
+  BPF_ASSERT(!pthread_create(&thread, &attr, ThreadFnc, &thread_ran));
+  BPF_ASSERT(!pthread_attr_destroy(&attr));
+  while (Syscall::Call(__NR_futex, &thread_ran, FUTEX_WAIT, 0, 0, 0, 0) ==
+         -EINTR) {
+  }
+  BPF_ASSERT(thread_ran);
+
+  // Attempt to fork() a process using clone(). This should fail. We use the
+  // same flags that glibc uses when calling fork(). But we don't actually
+  // try calling the fork() implementation in the C run-time library, as
+  // run-time libraries other than glibc might call __NR_fork instead of
+  // __NR_clone, and that would introduce a bogus test failure.
+  int pid;
+  BPF_ASSERT(Syscall::Call(__NR_clone,
+                           CLONE_CHILD_CLEARTID | CLONE_CHILD_SETTID | SIGCHLD,
+                           0,
+                           0,
+                           &pid) == -EPERM);
+}
+
+BPF_TEST_C(SandboxBPF, PthreadEquality, PthreadPolicyEquality) {
+  PthreadTest();
+}
+
+BPF_TEST_C(SandboxBPF, PthreadBitMask, PthreadPolicyBitMask) {
+  PthreadTest();
+}
+
+// libc might not define these even though the kernel supports it.
+#ifndef PTRACE_O_TRACESECCOMP
+#define PTRACE_O_TRACESECCOMP 0x00000080
+#endif
+
+#ifdef PTRACE_EVENT_SECCOMP
+#define IS_SECCOMP_EVENT(status) ((status >> 16) == PTRACE_EVENT_SECCOMP)
+#else
+// When Debian/Ubuntu backported seccomp-bpf support into earlier kernels, they
+// changed the value of PTRACE_EVENT_SECCOMP from 7 to 8, since 7 was taken by
+// PTRACE_EVENT_STOP (upstream chose to renumber PTRACE_EVENT_STOP to 128).  If
+// PTRACE_EVENT_SECCOMP isn't defined, we have no choice but to consider both
+// values here.
+#define IS_SECCOMP_EVENT(status) ((status >> 16) == 7 || (status >> 16) == 8)
+#endif
+
+#if defined(__arm__)
+#ifndef PTRACE_SET_SYSCALL
+#define PTRACE_SET_SYSCALL 23
+#endif
+#endif
+
+#if defined(__aarch64__)
+#ifndef PTRACE_GETREGS
+#define PTRACE_GETREGS 12
+#endif
+#endif
+
+#if defined(__aarch64__)
+#ifndef PTRACE_SETREGS
+#define PTRACE_SETREGS 13
+#endif
+#endif
+
+// Changes the syscall to run for a child being sandboxed using seccomp-bpf with
+// PTRACE_O_TRACESECCOMP.  Should only be called when the child is stopped on
+// PTRACE_EVENT_SECCOMP.
+//
+// regs should contain the current set of registers of the child, obtained using
+// PTRACE_GETREGS.
+//
+// Depending on the architecture, this may modify regs, so the caller is
+// responsible for committing these changes using PTRACE_SETREGS.
+long SetSyscall(pid_t pid, regs_struct* regs, int syscall_number) {
+#if defined(__arm__)
+  // On ARM, the syscall is changed using PTRACE_SET_SYSCALL.  We cannot use the
+  // libc ptrace call as the request parameter is an enum, and
+  // PTRACE_SET_SYSCALL may not be in the enum.
+  return syscall(__NR_ptrace, PTRACE_SET_SYSCALL, pid, NULL, syscall_number);
+#endif
+
+  SECCOMP_PT_SYSCALL(*regs) = syscall_number;
+  return 0;
+}
+
+const uint16_t kTraceData = 0xcc;
+
+class TraceAllPolicy : public SandboxBPFDSLPolicy {
+ public:
+  TraceAllPolicy() {}
+  virtual ~TraceAllPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int system_call_number) const override {
+    return Trace(kTraceData);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TraceAllPolicy);
+};
+
+SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(SeccompRetTrace)) {
+  if (SandboxBPF::SupportsSeccompSandbox(-1) !=
+      sandbox::SandboxBPF::STATUS_AVAILABLE) {
+    return;
+  }
+
+// This test is disabled on arm due to a kernel bug.
+// See https://code.google.com/p/chromium/issues/detail?id=383977
+#if defined(__arm__) || defined(__aarch64__)
+  printf("This test is currently disabled on ARM32/64 due to a kernel bug.");
+  return;
+#endif
+
+#if defined(__mips__)
+  // TODO: Figure out how to support specificity of handling indirect syscalls
+  //        in this test and enable it.
+  printf("This test is currently disabled on MIPS.");
+  return;
+#endif
+
+  pid_t pid = fork();
+  BPF_ASSERT_NE(-1, pid);
+  if (pid == 0) {
+    pid_t my_pid = getpid();
+    BPF_ASSERT_NE(-1, ptrace(PTRACE_TRACEME, -1, NULL, NULL));
+    BPF_ASSERT_EQ(0, raise(SIGSTOP));
+    SandboxBPF sandbox;
+    sandbox.SetSandboxPolicy(new TraceAllPolicy);
+    BPF_ASSERT(sandbox.StartSandbox(SandboxBPF::PROCESS_SINGLE_THREADED));
+
+    // getpid is allowed.
+    BPF_ASSERT_EQ(my_pid, syscall(__NR_getpid));
+
+    // write to stdout is skipped and returns a fake value.
+    BPF_ASSERT_EQ(kExpectedReturnValue,
+                  syscall(__NR_write, STDOUT_FILENO, "A", 1));
+
+    // kill is rewritten to exit(kExpectedReturnValue).
+    syscall(__NR_kill, my_pid, SIGKILL);
+
+    // Should not be reached.
+    BPF_ASSERT(false);
+  }
+
+  int status;
+  BPF_ASSERT(HANDLE_EINTR(waitpid(pid, &status, WUNTRACED)) != -1);
+  BPF_ASSERT(WIFSTOPPED(status));
+
+  BPF_ASSERT_NE(-1,
+                ptrace(PTRACE_SETOPTIONS,
+                       pid,
+                       NULL,
+                       reinterpret_cast<void*>(PTRACE_O_TRACESECCOMP)));
+  BPF_ASSERT_NE(-1, ptrace(PTRACE_CONT, pid, NULL, NULL));
+  while (true) {
+    BPF_ASSERT(HANDLE_EINTR(waitpid(pid, &status, 0)) != -1);
+    if (WIFEXITED(status) || WIFSIGNALED(status)) {
+      BPF_ASSERT(WIFEXITED(status));
+      BPF_ASSERT_EQ(kExpectedReturnValue, WEXITSTATUS(status));
+      break;
+    }
+
+    if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGTRAP ||
+        !IS_SECCOMP_EVENT(status)) {
+      BPF_ASSERT_NE(-1, ptrace(PTRACE_CONT, pid, NULL, NULL));
+      continue;
+    }
+
+    unsigned long data;
+    BPF_ASSERT_NE(-1, ptrace(PTRACE_GETEVENTMSG, pid, NULL, &data));
+    BPF_ASSERT_EQ(kTraceData, data);
+
+    regs_struct regs;
+    BPF_ASSERT_NE(-1, ptrace(PTRACE_GETREGS, pid, NULL, &regs));
+    switch (SECCOMP_PT_SYSCALL(regs)) {
+      case __NR_write:
+        // Skip writes to stdout, make it return kExpectedReturnValue.  Allow
+        // writes to stderr so that BPF_ASSERT messages show up.
+        if (SECCOMP_PT_PARM1(regs) == STDOUT_FILENO) {
+          BPF_ASSERT_NE(-1, SetSyscall(pid, &regs, -1));
+          SECCOMP_PT_RESULT(regs) = kExpectedReturnValue;
+          BPF_ASSERT_NE(-1, ptrace(PTRACE_SETREGS, pid, NULL, &regs));
+        }
+        break;
+
+      case __NR_kill:
+        // Rewrite to exit(kExpectedReturnValue).
+        BPF_ASSERT_NE(-1, SetSyscall(pid, &regs, __NR_exit));
+        SECCOMP_PT_PARM1(regs) = kExpectedReturnValue;
+        BPF_ASSERT_NE(-1, ptrace(PTRACE_SETREGS, pid, NULL, &regs));
+        break;
+
+      default:
+        // Allow all other syscalls.
+        break;
+    }
+
+    BPF_ASSERT_NE(-1, ptrace(PTRACE_CONT, pid, NULL, NULL));
+  }
+}
+
+// Android does not expose pread64 nor pwrite64.
+#if !defined(OS_ANDROID)
+
+bool FullPwrite64(int fd, const char* buffer, size_t count, off64_t offset) {
+  while (count > 0) {
+    const ssize_t transfered =
+        HANDLE_EINTR(pwrite64(fd, buffer, count, offset));
+    if (transfered <= 0 || static_cast<size_t>(transfered) > count) {
+      return false;
+    }
+    count -= transfered;
+    buffer += transfered;
+    offset += transfered;
+  }
+  return true;
+}
+
+bool FullPread64(int fd, char* buffer, size_t count, off64_t offset) {
+  while (count > 0) {
+    const ssize_t transfered = HANDLE_EINTR(pread64(fd, buffer, count, offset));
+    if (transfered <= 0 || static_cast<size_t>(transfered) > count) {
+      return false;
+    }
+    count -= transfered;
+    buffer += transfered;
+    offset += transfered;
+  }
+  return true;
+}
+
+bool pread_64_was_forwarded = false;
+
+class TrapPread64Policy : public SandboxBPFDSLPolicy {
+ public:
+  TrapPread64Policy() {}
+  virtual ~TrapPread64Policy() {}
+
+  virtual ResultExpr EvaluateSyscall(int system_call_number) const override {
+    // Set the global environment for unsafe traps once.
+    if (system_call_number == MIN_SYSCALL) {
+      EnableUnsafeTraps();
+    }
+
+    if (system_call_number == __NR_pread64) {
+      return UnsafeTrap(ForwardPreadHandler, NULL);
+    }
+    return Allow();
+  }
+
+ private:
+  static intptr_t ForwardPreadHandler(const struct arch_seccomp_data& args,
+                                      void* aux) {
+    BPF_ASSERT(args.nr == __NR_pread64);
+    pread_64_was_forwarded = true;
+
+    return SandboxBPF::ForwardSyscall(args);
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(TrapPread64Policy);
+};
+
+// pread(2) takes a 64 bits offset. On 32 bits systems, it will be split
+// between two arguments. In this test, we make sure that ForwardSyscall() can
+// forward it properly.
+BPF_TEST_C(SandboxBPF, Pread64, TrapPread64Policy) {
+  ScopedTemporaryFile temp_file;
+  const uint64_t kLargeOffset = (static_cast<uint64_t>(1) << 32) | 0xBEEF;
+  const char kTestString[] = "This is a test!";
+  BPF_ASSERT(FullPwrite64(
+      temp_file.fd(), kTestString, sizeof(kTestString), kLargeOffset));
+
+  char read_test_string[sizeof(kTestString)] = {0};
+  BPF_ASSERT(FullPread64(temp_file.fd(),
+                         read_test_string,
+                         sizeof(read_test_string),
+                         kLargeOffset));
+  BPF_ASSERT_EQ(0, memcmp(kTestString, read_test_string, sizeof(kTestString)));
+  BPF_ASSERT(pread_64_was_forwarded);
+}
+
+#endif  // !defined(OS_ANDROID)
+
+void* TsyncApplyToTwoThreadsFunc(void* cond_ptr) {
+  base::WaitableEvent* event = static_cast<base::WaitableEvent*>(cond_ptr);
+
+  // Wait for the main thread to signal that the filter has been applied.
+  if (!event->IsSignaled()) {
+    event->Wait();
+  }
+
+  BPF_ASSERT(event->IsSignaled());
+
+  BlacklistNanosleepPolicy::AssertNanosleepFails();
+
+  return NULL;
+}
+
+SANDBOX_TEST(SandboxBPF, Tsync) {
+  if (SandboxBPF::SupportsSeccompThreadFilterSynchronization() !=
+      SandboxBPF::STATUS_AVAILABLE) {
+    return;
+  }
+
+  base::WaitableEvent event(true, false);
+
+  // Create a thread on which to invoke the blocked syscall.
+  pthread_t thread;
+  BPF_ASSERT_EQ(
+      0, pthread_create(&thread, NULL, &TsyncApplyToTwoThreadsFunc, &event));
+
+  // Test that nanoseelp success.
+  const struct timespec ts = {0, 0};
+  BPF_ASSERT_EQ(0, HANDLE_EINTR(syscall(__NR_nanosleep, &ts, NULL)));
+
+  // Engage the sandbox.
+  SandboxBPF sandbox;
+  sandbox.SetSandboxPolicy(new BlacklistNanosleepPolicy());
+  BPF_ASSERT(sandbox.StartSandbox(SandboxBPF::PROCESS_MULTI_THREADED));
+
+  // This thread should have the filter applied as well.
+  BlacklistNanosleepPolicy::AssertNanosleepFails();
+
+  // Signal the condition to invoke the system call.
+  event.Signal();
+
+  // Wait for the thread to finish.
+  BPF_ASSERT_EQ(0, pthread_join(thread, NULL));
+}
+
+class AllowAllPolicy : public SandboxBPFDSLPolicy {
+ public:
+  AllowAllPolicy() {}
+  virtual ~AllowAllPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    return Allow();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AllowAllPolicy);
+};
+
+SANDBOX_DEATH_TEST(
+    SandboxBPF,
+    StartMultiThreadedAsSingleThreaded,
+    DEATH_MESSAGE("Cannot start sandbox; process is already multi-threaded")) {
+  base::Thread thread("sandbox.linux.StartMultiThreadedAsSingleThreaded");
+  BPF_ASSERT(thread.Start());
+
+  SandboxBPF sandbox;
+  sandbox.SetSandboxPolicy(new AllowAllPolicy());
+  BPF_ASSERT(!sandbox.StartSandbox(SandboxBPF::PROCESS_SINGLE_THREADED));
+}
+
+// http://crbug.com/407357
+#if !defined(THREAD_SANITIZER)
+SANDBOX_DEATH_TEST(
+    SandboxBPF,
+    StartSingleThreadedAsMultiThreaded,
+    DEATH_MESSAGE(
+        "Cannot start sandbox; process may be single-threaded when "
+        "reported as not")) {
+  SandboxBPF sandbox;
+  sandbox.SetSandboxPolicy(new AllowAllPolicy());
+  BPF_ASSERT(!sandbox.StartSandbox(SandboxBPF::PROCESS_MULTI_THREADED));
+}
+#endif  // !defined(THREAD_SANITIZER)
+
+// A stub handler for the UnsafeTrap. Never called.
+intptr_t NoOpHandler(const struct arch_seccomp_data& args, void*) {
+  return -1;
+}
+
+class UnsafeTrapWithCondPolicy : public SandboxBPFDSLPolicy {
+ public:
+  UnsafeTrapWithCondPolicy() {}
+  virtual ~UnsafeTrapWithCondPolicy() {}
+
+  virtual ResultExpr EvaluateSyscall(int sysno) const override {
+    DCHECK(SandboxBPF::IsValidSyscallNumber(sysno));
+    setenv(kSandboxDebuggingEnv, "t", 0);
+    Die::SuppressInfoMessages(true);
+
+    if (SandboxBPF::IsRequiredForUnsafeTrap(sysno))
+      return Allow();
+
+    switch (sysno) {
+      case __NR_uname: {
+        const Arg<uint32_t> arg(0);
+        return If(arg == 0, Allow()).Else(Error(EPERM));
+      }
+      case __NR_setgid: {
+        const Arg<uint32_t> arg(0);
+        return Switch(arg)
+            .Case(100, Error(ENOMEM))
+            .Case(200, Error(ENOSYS))
+            .Default(Error(EPERM));
+      }
+      case __NR_close:
+      case __NR_exit_group:
+      case __NR_write:
+        return Allow();
+      case __NR_getppid:
+        return UnsafeTrap(NoOpHandler, NULL);
+      default:
+        return Error(EPERM);
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(UnsafeTrapWithCondPolicy);
+};
+
+BPF_TEST_C(SandboxBPF, UnsafeTrapWithCond, UnsafeTrapWithCondPolicy) {
+  BPF_ASSERT_EQ(-1, syscall(__NR_uname, 0));
+  BPF_ASSERT_EQ(EFAULT, errno);
+
+  BPF_ASSERT_EQ(-1, syscall(__NR_uname, 1));
+  BPF_ASSERT_EQ(EPERM, errno);
+
+  BPF_ASSERT_EQ(-1, syscall(__NR_setgid, 100));
+  BPF_ASSERT_EQ(ENOMEM, errno);
+
+  BPF_ASSERT_EQ(-1, syscall(__NR_setgid, 200));
+  BPF_ASSERT_EQ(ENOSYS, errno);
+
+  BPF_ASSERT_EQ(-1, syscall(__NR_setgid, 300));
+  BPF_ASSERT_EQ(EPERM, errno);
+}
+
+}  // namespace
+
+}  // namespace bpf_dsl
+}  // namespace sandbox