xref: /external/compiler-rt/lib/asan/asan_poisoning.cc

//===-- asan_poisoning.cc ---------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is a part of AddressSanitizer, an address sanity checker.
//
// Memory poisoning that can be made by user application.
//===----------------------------------------------------------------------===//

#include "asan_interceptors.h"
#include "asan_interface.h"
#include "asan_internal.h"
#include "asan_mapping.h"

#include <algorithm>

namespace __asan {

struct ShadowSegmentEndpoint {
  uint8_t *chunk;
  int8_t offset;  // in [0, SHADOW_GRANULARITY)
  int8_t value;  // = *chunk;

  explicit ShadowSegmentEndpoint(uintptr_t address) {
    chunk = (uint8_t*)MemToShadow(address);
    offset = address & (SHADOW_GRANULARITY - 1);
    value = *chunk;
  }
};

}  // namespace __asan

// ---------------------- Interface ---------------- {{{1
using namespace __asan;  // NOLINT

// Current implementation of __asan_(un)poison_memory_region doesn't check
// that user program (un)poisons the memory it owns. It poisons memory
// conservatively, and unpoisons progressively to make sure asan shadow
// mapping invariant is preserved (see detailed mapping description here:
// http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm).
//
// * if user asks to poison region [left, right), the program poisons
// at least [left, AlignDown(right)).
// * if user asks to unpoison region [left, right), the program unpoisons
// at most [AlignDown(left), right).
void __asan_poison_memory_region(void const volatile *addr, size_t size) {
  if (!FLAG_allow_user_poisoning || size == 0) return;
  uintptr_t beg_addr = (uintptr_t)addr;
  uintptr_t end_addr = beg_addr + size;
  if (FLAG_v >= 1) {
    Printf("Trying to poison memory region [%p, %p)\n", beg_addr, end_addr);
  }
  ShadowSegmentEndpoint beg(beg_addr);
  ShadowSegmentEndpoint end(end_addr);
  if (beg.chunk == end.chunk) {
    CHECK(beg.offset < end.offset);
    int8_t value = beg.value;
    CHECK(value == end.value);
    // We can only poison memory if the byte in end.offset is unaddressable.
    // No need to re-poison memory if it is poisoned already.
    if (value > 0 && value <= end.offset) {
      if (beg.offset > 0) {
        *beg.chunk = std::min(value, beg.offset);
      } else {
        *beg.chunk = kAsanUserPoisonedMemoryMagic;
      }
    }
    return;
  }
  CHECK(beg.chunk < end.chunk);
  if (beg.offset > 0) {
    // Mark bytes from beg.offset as unaddressable.
    if (beg.value == 0) {
      *beg.chunk = beg.offset;
    } else {
      *beg.chunk = std::min(beg.value, beg.offset);
    }
    beg.chunk++;
  }
  real_memset(beg.chunk, kAsanUserPoisonedMemoryMagic, end.chunk - beg.chunk);
  // Poison if byte in end.offset is unaddressable.
  if (end.value > 0 && end.value <= end.offset) {
    *end.chunk = kAsanUserPoisonedMemoryMagic;
  }
}

void __asan_unpoison_memory_region(void const volatile *addr, size_t size) {
  if (!FLAG_allow_user_poisoning || size == 0) return;
  uintptr_t beg_addr = (uintptr_t)addr;
  uintptr_t end_addr = beg_addr + size;
  if (FLAG_v >= 1) {
    Printf("Trying to unpoison memory region [%p, %p)\n", beg_addr, end_addr);
  }
  ShadowSegmentEndpoint beg(beg_addr);
  ShadowSegmentEndpoint end(end_addr);
  if (beg.chunk == end.chunk) {
    CHECK(beg.offset < end.offset);
    int8_t value = beg.value;
    CHECK(value == end.value);
    // We unpoison memory bytes up to enbytes up to end.offset if it is not
    // unpoisoned already.
    if (value != 0) {
      *beg.chunk = std::max(value, end.offset);
    }
    return;
  }
  CHECK(beg.chunk < end.chunk);
  if (beg.offset > 0) {
    *beg.chunk = 0;
    beg.chunk++;
  }
  real_memset(beg.chunk, 0, end.chunk - beg.chunk);
  if (end.offset > 0 && end.value != 0) {
    *end.chunk = std::max(end.value, end.offset);
  }
}

bool __asan_address_is_poisoned(void const volatile *addr) {
  const size_t kAccessSize = 1;
  uintptr_t address = (uintptr_t)addr;
  uint8_t *shadow_address = (uint8_t*)MemToShadow(address);
  int8_t shadow_value = *shadow_address;
  if (shadow_value) {
    uint8_t last_accessed_byte = (address & (SHADOW_GRANULARITY - 1))
                                 + kAccessSize - 1;
    return (last_accessed_byte >= shadow_value);
  }
  return false;
}