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// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#include "components/gwp_asan/common/allocator_state.h"
#include <algorithm>
#include "base/bits.h"
#include "base/logging.h"
#include "base/memory/page_size.h"
#include "base/strings/stringprintf.h"
#include "base/threading/platform_thread.h"
#include "build/build_config.h"
namespace gwp_asan {
namespace internal {
AllocatorState::AllocatorState() = default;
AllocatorState::GetMetadataReturnType AllocatorState::GetMetadataForAddress(
uintptr_t exception_address,
const SlotMetadata* metadata_arr,
const MetadataIdx* slot_to_metadata,
MetadataIdx* metadata_idx,
std::string* error) const {
CHECK(IsValid());
CHECK(PointerIsMine(exception_address));
AllocatorState::SlotIdx slot_idx = GetNearestSlot(exception_address);
if (slot_idx >= total_reserved_pages) {
*error = base::StringPrintf("Bad slot index %u >= %zu", slot_idx,
total_reserved_pages);
return GetMetadataReturnType::kErrorBadSlot;
}
AllocatorState::MetadataIdx index = slot_to_metadata[slot_idx];
if (index == kInvalidMetadataIdx)
return GetMetadataReturnType::kGwpAsanCrashWithMissingMetadata;
if (index >= num_metadata) {
*error =
base::StringPrintf("Bad metadata index %u >= %zu", index, num_metadata);
return GetMetadataReturnType::kErrorBadMetadataIndex;
}
if (GetNearestSlot(metadata_arr[index].alloc_ptr) != slot_idx) {
*error = base::StringPrintf(
"Outdated metadata index %u: slot for %zx does not match %zx", index,
metadata_arr[index].alloc_ptr, exception_address);
return GetMetadataReturnType::kErrorOutdatedMetadataIndex;
}
*metadata_idx = index;
return GetMetadataReturnType::kGwpAsanCrash;
}
bool AllocatorState::IsValid() const {
if (!page_size || page_size != base::GetPageSize())
return false;
if (total_requested_pages == 0 || total_requested_pages > kMaxRequestedSlots)
return false;
if (total_reserved_pages == 0 || total_reserved_pages > kMaxReservedSlots ||
total_reserved_pages < total_requested_pages)
return false;
if (num_metadata == 0 ||
num_metadata > std::min(kMaxMetadata, total_requested_pages))
return false;
if (pages_base_addr % page_size != 0 || pages_end_addr % page_size != 0 ||
first_page_addr % page_size != 0)
return false;
if (pages_base_addr >= pages_end_addr)
return false;
if (first_page_addr != pages_base_addr + page_size ||
pages_end_addr - pages_base_addr !=
page_size * (total_reserved_pages * 2 + 1))
return false;
if (!metadata_addr || !slot_to_metadata_addr)
return false;
return true;
}
uintptr_t AllocatorState::GetPageAddr(uintptr_t addr) const {
const uintptr_t addr_mask = ~(page_size - 1ULL);
return addr & addr_mask;
}
uintptr_t AllocatorState::GetNearestValidPage(uintptr_t addr) const {
if (addr < first_page_addr)
return first_page_addr;
const uintptr_t last_page_addr = pages_end_addr - 2 * page_size;
if (addr > last_page_addr)
return last_page_addr;
uintptr_t offset = addr - first_page_addr;
// If addr is already on a valid page, just return addr.
if ((offset >> base::bits::Log2Floor(page_size)) % 2 == 0)
return addr;
// ptr points to a guard page, so get nearest valid page.
const size_t kHalfPageSize = page_size / 2;
if ((offset >> base::bits::Log2Floor(kHalfPageSize)) % 2 == 0) {
return addr - kHalfPageSize; // Round down.
}
return addr + kHalfPageSize; // Round up.
}
AllocatorState::SlotIdx AllocatorState::GetNearestSlot(uintptr_t addr) const {
return AddrToSlot(GetPageAddr(GetNearestValidPage(addr)));
}
AllocatorState::ErrorType AllocatorState::GetErrorType(uintptr_t addr,
bool allocated,
bool deallocated) const {
if (free_invalid_address)
return ErrorType::kFreeInvalidAddress;
if (!allocated)
return ErrorType::kUnknown;
if (double_free_address)
return ErrorType::kDoubleFree;
if (deallocated)
return ErrorType::kUseAfterFree;
if (addr < first_page_addr)
return ErrorType::kBufferUnderflow;
const uintptr_t last_page_addr = pages_end_addr - 2 * page_size;
if (addr > last_page_addr)
return ErrorType::kBufferOverflow;
const uintptr_t offset = addr - first_page_addr;
// If we hit this condition, it means we crashed on accessing an allocation
// even though it's currently allocated [there is a if(deallocated) return
// earlier.] This can happen when a use-after-free causes a crash and another
// thread manages to allocate the page in another thread before it's stopped.
// This can happen with low sampling frequencies and high parallel allocator
// usage.
if ((offset >> base::bits::Log2Floor(page_size)) % 2 == 0) {
LOG(WARNING) << "Hit impossible error condition, likely caused by a racy "
"use-after-free";
return ErrorType::kUnknown;
}
const size_t kHalfPageSize = page_size / 2;
return (offset >> base::bits::Log2Floor(kHalfPageSize)) % 2 == 0
? ErrorType::kBufferOverflow
: ErrorType::kBufferUnderflow;
}
uintptr_t AllocatorState::SlotToAddr(AllocatorState::SlotIdx slot) const {
DCHECK_LE(slot, kMaxReservedSlots);
return first_page_addr + 2 * slot * page_size;
}
AllocatorState::SlotIdx AllocatorState::AddrToSlot(uintptr_t addr) const {
DCHECK_EQ(addr % page_size, 0ULL);
uintptr_t offset = addr - first_page_addr;
DCHECK_EQ((offset >> base::bits::Log2Floor(page_size)) % 2, 0ULL);
size_t slot = (offset >> base::bits::Log2Floor(page_size)) / 2;
DCHECK_LE(slot, kMaxReservedSlots);
return static_cast<SlotIdx>(slot);
}
AllocatorState::SlotMetadata::SlotMetadata() = default;
} // namespace internal
} // namespace gwp_asan
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