Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/seccomp-bpf/verifier.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/seccomp-bpf/verifier.h"
+
+#include <string.h>
+
+#include <limits>
+
+#include "sandbox/linux/bpf_dsl/bpf_dsl.h"
+#include "sandbox/linux/bpf_dsl/bpf_dsl_impl.h"
+#include "sandbox/linux/bpf_dsl/policy_compiler.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_iterator.h"
+
+namespace sandbox {
+
+namespace {
+
+const uint64_t kLower32Bits = std::numeric_limits<uint32_t>::max();
+const uint64_t kUpper32Bits = static_cast<uint64_t>(kLower32Bits) << 32;
+const uint64_t kFull64Bits = std::numeric_limits<uint64_t>::max();
+
+struct State {
+  State(const std::vector<struct sock_filter>& p,
+        const struct arch_seccomp_data& d)
+      : program(p), data(d), ip(0), accumulator(0), acc_is_valid(false) {}
+  const std::vector<struct sock_filter>& program;
+  const struct arch_seccomp_data& data;
+  unsigned int ip;
+  uint32_t accumulator;
+  bool acc_is_valid;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(State);
+};
+
+uint32_t EvaluateErrorCode(bpf_dsl::PolicyCompiler* compiler,
+                           const ErrorCode& code,
+                           const struct arch_seccomp_data& data) {
+  if (code.error_type() == ErrorCode::ET_SIMPLE ||
+      code.error_type() == ErrorCode::ET_TRAP) {
+    return code.err();
+  } else if (code.error_type() == ErrorCode::ET_COND) {
+    if (code.width() == ErrorCode::TP_32BIT &&
+        (data.args[code.argno()] >> 32) &&
+        (data.args[code.argno()] & 0xFFFFFFFF80000000ull) !=
+            0xFFFFFFFF80000000ull) {
+      return compiler->Unexpected64bitArgument().err();
+    }
+    bool equal = (data.args[code.argno()] & code.mask()) == code.value();
+    return EvaluateErrorCode(
+        compiler, equal ? *code.passed() : *code.failed(), data);
+  } else {
+    return SECCOMP_RET_INVALID;
+  }
+}
+
+bool VerifyErrorCode(bpf_dsl::PolicyCompiler* compiler,
+                     const std::vector<struct sock_filter>& program,
+                     struct arch_seccomp_data* data,
+                     const ErrorCode& root_code,
+                     const ErrorCode& code,
+                     const char** err) {
+  if (code.error_type() == ErrorCode::ET_SIMPLE ||
+      code.error_type() == ErrorCode::ET_TRAP) {
+    uint32_t computed_ret = Verifier::EvaluateBPF(program, *data, err);
+    if (*err) {
+      return false;
+    } else if (computed_ret != EvaluateErrorCode(compiler, root_code, *data)) {
+      // For efficiency's sake, we'd much rather compare "computed_ret"
+      // against "code.err()". This works most of the time, but it doesn't
+      // always work for nested conditional expressions. The test values
+      // that we generate on the fly to probe expressions can trigger
+      // code flow decisions in multiple nodes of the decision tree, and the
+      // only way to compute the correct error code in that situation is by
+      // calling EvaluateErrorCode().
+      *err = "Exit code from BPF program doesn't match";
+      return false;
+    }
+  } else if (code.error_type() == ErrorCode::ET_COND) {
+    if (code.argno() < 0 || code.argno() >= 6) {
+      *err = "Invalid argument number in error code";
+      return false;
+    }
+
+    // TODO(mdempsky): The test values generated here try to provide good
+    // coverage for generated BPF instructions while avoiding combinatorial
+    // explosion on large policies. Ideally we would instead take a fuzzing-like
+    // approach and generate a bounded number of test cases regardless of policy
+    // size.
+
+    // Verify that we can check a value for simple equality.
+    data->args[code.argno()] = code.value();
+    if (!VerifyErrorCode(
+            compiler, program, data, root_code, *code.passed(), err)) {
+      return false;
+    }
+
+    // If mask ignores any bits, verify that setting those bits is still
+    // detected as equality.
+    uint64_t ignored_bits = ~code.mask();
+    if (code.width() == ErrorCode::TP_32BIT) {
+      ignored_bits = static_cast<uint32_t>(ignored_bits);
+    }
+    if ((ignored_bits & kLower32Bits) != 0) {
+      data->args[code.argno()] = code.value() | (ignored_bits & kLower32Bits);
+      if (!VerifyErrorCode(
+              compiler, program, data, root_code, *code.passed(), err)) {
+        return false;
+      }
+    }
+    if ((ignored_bits & kUpper32Bits) != 0) {
+      data->args[code.argno()] = code.value() | (ignored_bits & kUpper32Bits);
+      if (!VerifyErrorCode(
+              compiler, program, data, root_code, *code.passed(), err)) {
+        return false;
+      }
+    }
+
+    // Verify that changing bits included in the mask is detected as inequality.
+    if ((code.mask() & kLower32Bits) != 0) {
+      data->args[code.argno()] = code.value() ^ (code.mask() & kLower32Bits);
+      if (!VerifyErrorCode(
+              compiler, program, data, root_code, *code.failed(), err)) {
+        return false;
+      }
+    }
+    if ((code.mask() & kUpper32Bits) != 0) {
+      data->args[code.argno()] = code.value() ^ (code.mask() & kUpper32Bits);
+      if (!VerifyErrorCode(
+              compiler, program, data, root_code, *code.failed(), err)) {
+        return false;
+      }
+    }
+
+    if (code.width() == ErrorCode::TP_32BIT) {
+      // For 32-bit system call arguments, we emit additional instructions to
+      // validate the upper 32-bits. Here we test that validation.
+
+      // Arbitrary 64-bit values should be rejected.
+      data->args[code.argno()] = 1ULL << 32;
+      if (!VerifyErrorCode(compiler,
+                           program,
+                           data,
+                           root_code,
+                           compiler->Unexpected64bitArgument(),
+                           err)) {
+        return false;
+      }
+
+      // Upper 32-bits set without the MSB of the lower 32-bits set should be
+      // rejected too.
+      data->args[code.argno()] = kUpper32Bits;
+      if (!VerifyErrorCode(compiler,
+                           program,
+                           data,
+                           root_code,
+                           compiler->Unexpected64bitArgument(),
+                           err)) {
+        return false;
+      }
+    }
+  } else {
+    *err = "Attempting to return invalid error code from BPF program";
+    return false;
+  }
+  return true;
+}
+
+void Ld(State* state, const struct sock_filter& insn, const char** err) {
+  if (BPF_SIZE(insn.code) != BPF_W || BPF_MODE(insn.code) != BPF_ABS ||
+      insn.jt != 0 || insn.jf != 0) {
+    *err = "Invalid BPF_LD instruction";
+    return;
+  }
+  if (insn.k < sizeof(struct arch_seccomp_data) && (insn.k & 3) == 0) {
+    // We only allow loading of properly aligned 32bit quantities.
+    memcpy(&state->accumulator,
+           reinterpret_cast<const char*>(&state->data) + insn.k,
+           4);
+  } else {
+    *err = "Invalid operand in BPF_LD instruction";
+    return;
+  }
+  state->acc_is_valid = true;
+  return;
+}
+
+void Jmp(State* state, const struct sock_filter& insn, const char** err) {
+  if (BPF_OP(insn.code) == BPF_JA) {
+    if (state->ip + insn.k + 1 >= state->program.size() ||
+        state->ip + insn.k + 1 <= state->ip) {
+    compilation_failure:
+      *err = "Invalid BPF_JMP instruction";
+      return;
+    }
+    state->ip += insn.k;
+  } else {
+    if (BPF_SRC(insn.code) != BPF_K || !state->acc_is_valid ||
+        state->ip + insn.jt + 1 >= state->program.size() ||
+        state->ip + insn.jf + 1 >= state->program.size()) {
+      goto compilation_failure;
+    }
+    switch (BPF_OP(insn.code)) {
+      case BPF_JEQ:
+        if (state->accumulator == insn.k) {
+          state->ip += insn.jt;
+        } else {
+          state->ip += insn.jf;
+        }
+        break;
+      case BPF_JGT:
+        if (state->accumulator > insn.k) {
+          state->ip += insn.jt;
+        } else {
+          state->ip += insn.jf;
+        }
+        break;
+      case BPF_JGE:
+        if (state->accumulator >= insn.k) {
+          state->ip += insn.jt;
+        } else {
+          state->ip += insn.jf;
+        }
+        break;
+      case BPF_JSET:
+        if (state->accumulator & insn.k) {
+          state->ip += insn.jt;
+        } else {
+          state->ip += insn.jf;
+        }
+        break;
+      default:
+        goto compilation_failure;
+    }
+  }
+}
+
+uint32_t Ret(State*, const struct sock_filter& insn, const char** err) {
+  if (BPF_SRC(insn.code) != BPF_K) {
+    *err = "Invalid BPF_RET instruction";
+    return 0;
+  }
+  return insn.k;
+}
+
+void Alu(State* state, const struct sock_filter& insn, const char** err) {
+  if (BPF_OP(insn.code) == BPF_NEG) {
+    state->accumulator = -state->accumulator;
+    return;
+  } else {
+    if (BPF_SRC(insn.code) != BPF_K) {
+      *err = "Unexpected source operand in arithmetic operation";
+      return;
+    }
+    switch (BPF_OP(insn.code)) {
+      case BPF_ADD:
+        state->accumulator += insn.k;
+        break;
+      case BPF_SUB:
+        state->accumulator -= insn.k;
+        break;
+      case BPF_MUL:
+        state->accumulator *= insn.k;
+        break;
+      case BPF_DIV:
+        if (!insn.k) {
+          *err = "Illegal division by zero";
+          break;
+        }
+        state->accumulator /= insn.k;
+        break;
+      case BPF_MOD:
+        if (!insn.k) {
+          *err = "Illegal division by zero";
+          break;
+        }
+        state->accumulator %= insn.k;
+        break;
+      case BPF_OR:
+        state->accumulator |= insn.k;
+        break;
+      case BPF_XOR:
+        state->accumulator ^= insn.k;
+        break;
+      case BPF_AND:
+        state->accumulator &= insn.k;
+        break;
+      case BPF_LSH:
+        if (insn.k > 32) {
+          *err = "Illegal shift operation";
+          break;
+        }
+        state->accumulator <<= insn.k;
+        break;
+      case BPF_RSH:
+        if (insn.k > 32) {
+          *err = "Illegal shift operation";
+          break;
+        }
+        state->accumulator >>= insn.k;
+        break;
+      default:
+        *err = "Invalid operator in arithmetic operation";
+        break;
+    }
+  }
+}
+
+}  // namespace
+
+bool Verifier::VerifyBPF(bpf_dsl::PolicyCompiler* compiler,
+                         const std::vector<struct sock_filter>& program,
+                         const bpf_dsl::SandboxBPFDSLPolicy& policy,
+                         const char** err) {
+  *err = NULL;
+  for (uint32_t sysnum : SyscallSet::All()) {
+    // We ideally want to iterate over the full system call range and values
+    // just above and just below this range. This gives us the full result set
+    // of the "evaluators".
+    // On Intel systems, this can fail in a surprising way, as a cleared bit 30
+    // indicates either i386 or x86-64; and a set bit 30 indicates x32. And
+    // unless we pay attention to setting this bit correctly, an early check in
+    // our BPF program will make us fail with a misleading error code.
+    struct arch_seccomp_data data = {static_cast<int>(sysnum),
+                                     static_cast<uint32_t>(SECCOMP_ARCH)};
+#if defined(__i386__) || defined(__x86_64__)
+#if defined(__x86_64__) && defined(__ILP32__)
+    if (!(sysnum & 0x40000000u)) {
+      continue;
+    }
+#else
+    if (sysnum & 0x40000000u) {
+      continue;
+    }
+#endif
+#endif
+    ErrorCode code = SyscallSet::IsValid(sysnum)
+                         ? policy.EvaluateSyscall(sysnum)->Compile(compiler)
+                         : policy.InvalidSyscall()->Compile(compiler);
+    if (!VerifyErrorCode(compiler, program, &data, code, code, err)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+uint32_t Verifier::EvaluateBPF(const std::vector<struct sock_filter>& program,
+                               const struct arch_seccomp_data& data,
+                               const char** err) {
+  *err = NULL;
+  if (program.size() < 1 || program.size() >= SECCOMP_MAX_PROGRAM_SIZE) {
+    *err = "Invalid program length";
+    return 0;
+  }
+  for (State state(program, data); !*err; ++state.ip) {
+    if (state.ip >= program.size()) {
+      *err = "Invalid instruction pointer in BPF program";
+      break;
+    }
+    const struct sock_filter& insn = program[state.ip];
+    switch (BPF_CLASS(insn.code)) {
+      case BPF_LD:
+        Ld(&state, insn, err);
+        break;
+      case BPF_JMP:
+        Jmp(&state, insn, err);
+        break;
+      case BPF_RET: {
+        uint32_t r = Ret(&state, insn, err);
+        switch (r & SECCOMP_RET_ACTION) {
+          case SECCOMP_RET_TRAP:
+          case SECCOMP_RET_ERRNO:
+          case SECCOMP_RET_TRACE:
+          case SECCOMP_RET_ALLOW:
+            break;
+          case SECCOMP_RET_KILL:     // We don't ever generate this
+          case SECCOMP_RET_INVALID:  // Should never show up in BPF program
+          default:
+            *err = "Unexpected return code found in BPF program";
+            return 0;
+        }
+        return r;
+      }
+      case BPF_ALU:
+        Alu(&state, insn, err);
+        break;
+      default:
+        *err = "Unexpected instruction in BPF program";
+        break;
+    }
+  }
+  return 0;
+}
+
+}  // namespace sandbox