Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/seccomp-bpf/errorcode.h

+// 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.
+
+#ifndef SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__
+#define SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__
+
+#include "sandbox/linux/seccomp-bpf/trap.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+namespace bpf_dsl {
+class PolicyCompiler;
+}
+
+// This class holds all the possible values that can be returned by a sandbox
+// policy.
+// We can either wrap a symbolic ErrorCode (i.e. ERR_XXX enum values), an
+// errno value (in the range 0..4095), a pointer to a TrapFnc callback
+// handling a SECCOMP_RET_TRAP trap, or a complex constraint.
+// All of the commonly used values are stored in the "err_" field. So, code
+// that is using the ErrorCode class typically operates on a single 32bit
+// field.
+class SANDBOX_EXPORT ErrorCode {
+ public:
+  enum {
+    // Allow this system call. The value of ERR_ALLOWED is pretty much
+    // completely arbitrary. But we want to pick it so that is is unlikely
+    // to be passed in accidentally, when the user intended to return an
+    // "errno" (see below) value instead.
+    ERR_ALLOWED = 0x04000000,
+
+    // If the progress is being ptraced with PTRACE_O_TRACESECCOMP, then the
+    // tracer will be notified of a PTRACE_EVENT_SECCOMP and allowed to change
+    // or skip the system call.  The lower 16 bits of err will be available to
+    // the tracer via PTRACE_GETEVENTMSG.
+    ERR_TRACE   = 0x08000000,
+
+    // Deny the system call with a particular "errno" value.
+    // N.B.: It is also possible to return "0" here. That would normally
+    //       indicate success, but it won't actually run the system call.
+    //       This is very different from return ERR_ALLOWED.
+    ERR_MIN_ERRNO = 0,
+#if defined(__mips__)
+    // MIPS only supports errno up to 1133
+    ERR_MAX_ERRNO = 1133,
+#else
+    // TODO(markus): Android only supports errno up to 255
+    // (crbug.com/181647).
+    ERR_MAX_ERRNO = 4095,
+#endif
+  };
+
+  // While BPF filter programs always operate on 32bit quantities, the kernel
+  // always sees system call arguments as 64bit values. This statement is true
+  // no matter whether the host system is natively operating in 32bit or 64bit.
+  // The BPF compiler hides the fact that BPF instructions cannot directly
+  // access 64bit quantities. But policies are still advised to specify whether
+  // a system call expects a 32bit or a 64bit quantity.
+  enum ArgType {
+    // When passed as an argument to SandboxBPF::Cond(), TP_32BIT requests that
+    // the conditional test should operate on the 32bit part of the system call
+    // argument.
+    // On 64bit architectures, this verifies that user space did not pass
+    // a 64bit value as an argument to the system call. If it did, that will be
+    // interpreted as an attempt at breaking the sandbox and results in the
+    // program getting terminated.
+    // In other words, only perform a 32bit test, if you are sure this
+    // particular system call would never legitimately take a 64bit
+    // argument.
+    // Implementation detail: TP_32BIT does two things. 1) it restricts the
+    // conditional test to operating on the LSB only, and 2) it adds code to
+    // the BPF filter program verifying that the MSB  the kernel received from
+    // user space is either 0, or 0xFFFFFFFF; the latter is acceptable, iff bit
+    // 31 was set in the system call argument. It deals with 32bit arguments
+    // having been sign extended.
+    TP_32BIT,
+
+    // When passed as an argument to SandboxBPF::Cond(), TP_64BIT requests that
+    // the conditional test should operate on the full 64bit argument. It is
+    // generally harmless to perform a 64bit test on 32bit systems, as the
+    // kernel will always see the top 32 bits of all arguments as zero'd out.
+    // This approach has the desirable property that for tests of pointer
+    // values, we can always use TP_64BIT no matter the host architecture.
+    // But of course, that also means, it is possible to write conditional
+    // policies that turn into no-ops on 32bit systems; this is by design.
+    TP_64BIT,
+  };
+
+  // Deprecated.
+  enum Operation {
+    // Test whether the system call argument is equal to the operand.
+    OP_EQUAL,
+
+    // Tests a system call argument against a bit mask.
+    // The "ALL_BITS" variant performs this test: "arg & mask == mask"
+    // This implies that a mask of zero always results in a passing test.
+    // The "ANY_BITS" variant performs this test: "arg & mask != 0"
+    // This implies that a mask of zero always results in a failing test.
+    OP_HAS_ALL_BITS,
+    OP_HAS_ANY_BITS,
+  };
+
+  enum ErrorType {
+    ET_INVALID,
+    ET_SIMPLE,
+    ET_TRAP,
+    ET_COND,
+  };
+
+  // We allow the default constructor, as it makes the ErrorCode class
+  // much easier to use. But if we ever encounter an invalid ErrorCode
+  // when compiling a BPF filter, we deliberately generate an invalid
+  // program that will get flagged both by our Verifier class and by
+  // the Linux kernel.
+  ErrorCode();
+  explicit ErrorCode(int err);
+
+  // For all practical purposes, ErrorCodes are treated as if they were
+  // structs. The copy constructor and assignment operator are trivial and
+  // we do not need to explicitly specify them.
+  // Most notably, it is in fact perfectly OK to directly copy the passed_ and
+  // failed_ field. They only ever get set by our private constructor, and the
+  // callers handle life-cycle management for these objects.
+
+  // Destructor
+  ~ErrorCode() {}
+
+  bool Equals(const ErrorCode& err) const;
+  bool LessThan(const ErrorCode& err) const;
+
+  uint32_t err() const { return err_; }
+  ErrorType error_type() const { return error_type_; }
+
+  bool safe() const { return safe_; }
+
+  uint64_t mask() const { return mask_; }
+  uint64_t value() const { return value_; }
+  int argno() const { return argno_; }
+  ArgType width() const { return width_; }
+  const ErrorCode* passed() const { return passed_; }
+  const ErrorCode* failed() const { return failed_; }
+
+  struct LessThan {
+    bool operator()(const ErrorCode& a, const ErrorCode& b) const {
+      return a.LessThan(b);
+    }
+  };
+
+ private:
+  friend bpf_dsl::PolicyCompiler;
+  friend class CodeGen;
+  friend class SandboxBPF;
+  friend class Trap;
+
+  // If we are wrapping a callback, we must assign a unique id. This id is
+  // how the kernel tells us which one of our different SECCOMP_RET_TRAP
+  // cases has been triggered.
+  ErrorCode(uint16_t trap_id, Trap::TrapFnc fnc, const void* aux, bool safe);
+
+  // Some system calls require inspection of arguments. This constructor
+  // allows us to specify additional constraints.
+  ErrorCode(int argno,
+            ArgType width,
+            uint64_t mask,
+            uint64_t value,
+            const ErrorCode* passed,
+            const ErrorCode* failed);
+
+  ErrorType error_type_;
+
+  union {
+    // Fields needed for SECCOMP_RET_TRAP callbacks
+    struct {
+      Trap::TrapFnc fnc_;  // Callback function and arg, if trap was
+      void* aux_;          //   triggered by the kernel's BPF filter.
+      bool safe_;          // Keep sandbox active while calling fnc_()
+    };
+
+    // Fields needed when inspecting additional arguments.
+    struct {
+      uint64_t mask_;            // Mask that we are comparing under.
+      uint64_t value_;           // Value that we are comparing with.
+      int argno_;                // Syscall arg number that we are inspecting.
+      ArgType width_;            // Whether we are looking at a 32/64bit value.
+      const ErrorCode* passed_;  // Value to be returned if comparison passed,
+      const ErrorCode* failed_;  //   or if it failed.
+    };
+  };
+
+  // 32bit field used for all possible types of ErrorCode values. This is
+  // the value that uniquely identifies any ErrorCode and it (typically) can
+  // be emitted directly into a BPF filter program.
+  uint32_t err_;
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__