sandbox/linux/seccomp-bpf/syscall_iterator.cc

   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
  10 namespace sandbox {
  11
  12 uint32_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
  72 bool 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__))
  84 bool 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
  89 bool SyscallIterator::IsArmPrivate(uint32_t) { return false; }
  90 #endif
  91
  92 }  // namespace sandbox