syscall_iterator.cc revision a3f6a49ab37290eeeb8db0f41ec0f1cb74a68be7 
1// Copyright (c) 2012 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "sandbox/linux/seccomp-bpf/syscall_iterator.h"
6
7#include "base/basictypes.h"
8#include "sandbox/linux/seccomp-bpf/linux_seccomp.h"
9
10namespace sandbox {
11
12uint32_t SyscallIterator::Next() {
13  if (done_) {
14    return num_;
15  }
16
17  uint32_t val;
18  do {
19    // |num_| has been initialized to 0, which we assume is also MIN_SYSCALL.
20    // This true for supported architectures (Intel and ARM EABI).
21    COMPILE_ASSERT(MIN_SYSCALL == 0u, min_syscall_should_always_be_zero);
22    val = num_;
23
24    // First we iterate up to MAX_PUBLIC_SYSCALL, which is equal to MAX_SYSCALL
25    // on Intel architectures, but leaves room for private syscalls on ARM.
26    if (num_ <= MAX_PUBLIC_SYSCALL) {
27      if (invalid_only_ && num_ < MAX_PUBLIC_SYSCALL) {
28        num_ = MAX_PUBLIC_SYSCALL;
29      } else {
30        ++num_;
31      }
32#if defined(__arm__)
33      // ARM EABI includes "ARM private" system calls starting at
34      // MIN_PRIVATE_SYSCALL, and a "ghost syscall private to the kernel" at
35      // MIN_GHOST_SYSCALL.
36    } else if (num_ < MIN_PRIVATE_SYSCALL - 1) {
37      num_ = MIN_PRIVATE_SYSCALL - 1;
38    } else if (num_ <= MAX_PRIVATE_SYSCALL) {
39      if (invalid_only_ && num_ < MAX_PRIVATE_SYSCALL) {
40        num_ = MAX_PRIVATE_SYSCALL;
41      } else {
42        ++num_;
43      }
44    } else if (num_ < MIN_GHOST_SYSCALL - 1) {
45      num_ = MIN_GHOST_SYSCALL - 1;
46    } else if (num_ <= MAX_SYSCALL) {
47      if (invalid_only_ && num_ < MAX_SYSCALL) {
48        num_ = MAX_SYSCALL;
49      } else {
50        ++num_;
51      }
52#endif
53      // BPF programs only ever operate on unsigned quantities. So, that's how
54      // we iterate; we return values from 0..0xFFFFFFFFu. But there are places,
55      // where the kernel might interpret system call numbers as signed
56      // quantities, so the boundaries between signed and unsigned values are
57      // potential problem cases. We want to explicitly return these values from
58      // our iterator.
59    } else if (num_ < 0x7FFFFFFFu) {
60      num_ = 0x7FFFFFFFu;
61    } else if (num_ < 0x80000000u) {
62      num_ = 0x80000000u;
63    } else if (num_ < 0xFFFFFFFFu) {
64      num_ = 0xFFFFFFFFu;
65    }
66  } while (invalid_only_ && IsValid(val));
67
68  done_ |= val == 0xFFFFFFFFu;
69  return val;
70}
71
72bool SyscallIterator::IsValid(uint32_t num) {
73  uint32_t min_syscall = MIN_SYSCALL;
74  if (num >= min_syscall && num <= MAX_PUBLIC_SYSCALL) {
75    return true;
76  }
77  if (IsArmPrivate(num)) {
78    return true;
79  }
80  return false;
81}
82
83#if defined(__arm__) && (defined(__thumb__) || defined(__ARM_EABI__))
84bool SyscallIterator::IsArmPrivate(uint32_t num) {
85  return (num >= MIN_PRIVATE_SYSCALL && num <= MAX_PRIVATE_SYSCALL) ||
86         (num >= MIN_GHOST_SYSCALL && num <= MAX_SYSCALL);
87}
88#else
89bool SyscallIterator::IsArmPrivate(uint32_t) { return false; }
90#endif
91
92}  // namespace sandbox
93