blob: 7cd3867435b04295572e40b0dda4477c20c2ab75 [file] [log] [blame]
//===-- combined.h ----------------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "chunk.h"
#include "common.h"
#include "flags.h"
#include "flags_parser.h"
#include "local_cache.h"
#include "memtag.h"
#include "options.h"
#include "quarantine.h"
#include "report.h"
#include "secondary.h"
#include "stack_depot.h"
#include "string_utils.h"
#include "tsd.h"
#include "scudo/interface.h"
#include "gwp_asan/guarded_pool_allocator.h"
#include "gwp_asan/optional/backtrace.h"
#include "gwp_asan/optional/segv_handler.h"
#endif // GWP_ASAN_HOOKS
extern "C" inline void EmptyCallback() {}
// This function is not part of the NDK so it does not appear in any public
// header files. We only declare/use it when targeting the platform.
extern "C" size_t android_unsafe_frame_pointer_chase(scudo::uptr *buf,
size_t num_entries);
namespace scudo {
template <class Params, void (*PostInitCallback)(void) = EmptyCallback>
class Allocator {
using PrimaryT = typename Params::Primary;
using CacheT = typename PrimaryT::CacheT;
typedef Allocator<Params, PostInitCallback> ThisT;
typedef typename Params::template TSDRegistryT<ThisT> TSDRegistryT;
void callPostInitCallback() {
static pthread_once_t OnceControl = PTHREAD_ONCE_INIT;
pthread_once(&OnceControl, PostInitCallback);
struct QuarantineCallback {
explicit QuarantineCallback(ThisT &Instance, CacheT &LocalCache)
: Allocator(Instance), Cache(LocalCache) {}
// Chunk recycling function, returns a quarantined chunk to the backend,
// first making sure it hasn't been tampered with.
void recycle(void *Ptr) {
Chunk::UnpackedHeader Header;
Chunk::loadHeader(Allocator.Cookie, Ptr, &Header);
if (UNLIKELY(Header.State != Chunk::State::Quarantined))
reportInvalidChunkState(AllocatorAction::Recycling, Ptr);
Chunk::UnpackedHeader NewHeader = Header;
NewHeader.State = Chunk::State::Available;
Chunk::compareExchangeHeader(Allocator.Cookie, Ptr, &NewHeader, &Header);
if (allocatorSupportsMemoryTagging<Params>())
Ptr = untagPointer(Ptr);
void *BlockBegin = Allocator::getBlockBegin(Ptr, &NewHeader);
Cache.deallocate(NewHeader.ClassId, BlockBegin);
// We take a shortcut when allocating a quarantine batch by working with the
// appropriate class ID instead of using Size. The compiler should optimize
// the class ID computation and work with the associated cache directly.
void *allocate(UNUSED uptr Size) {
const uptr QuarantineClassId = SizeClassMap::getClassIdBySize(
sizeof(QuarantineBatch) + Chunk::getHeaderSize());
void *Ptr = Cache.allocate(QuarantineClassId);
// Quarantine batch allocation failure is fatal.
if (UNLIKELY(!Ptr))
Ptr = reinterpret_cast<void *>(reinterpret_cast<uptr>(Ptr) +
Chunk::UnpackedHeader Header = {};
Header.ClassId = QuarantineClassId & Chunk::ClassIdMask;
Header.SizeOrUnusedBytes = sizeof(QuarantineBatch);
Header.State = Chunk::State::Allocated;
Chunk::storeHeader(Allocator.Cookie, Ptr, &Header);
// Reset tag to 0 as this chunk may have been previously used for a tagged
// user allocation.
if (UNLIKELY(useMemoryTagging<Params>(Allocator.Primary.Options.load())))
reinterpret_cast<uptr>(Ptr) + sizeof(QuarantineBatch));
return Ptr;
void deallocate(void *Ptr) {
const uptr QuarantineClassId = SizeClassMap::getClassIdBySize(
sizeof(QuarantineBatch) + Chunk::getHeaderSize());
Chunk::UnpackedHeader Header;
Chunk::loadHeader(Allocator.Cookie, Ptr, &Header);
if (UNLIKELY(Header.State != Chunk::State::Allocated))
reportInvalidChunkState(AllocatorAction::Deallocating, Ptr);
DCHECK_EQ(Header.ClassId, QuarantineClassId);
DCHECK_EQ(Header.Offset, 0);
DCHECK_EQ(Header.SizeOrUnusedBytes, sizeof(QuarantineBatch));
Chunk::UnpackedHeader NewHeader = Header;
NewHeader.State = Chunk::State::Available;
Chunk::compareExchangeHeader(Allocator.Cookie, Ptr, &NewHeader, &Header);
reinterpret_cast<void *>(reinterpret_cast<uptr>(Ptr) -
ThisT &Allocator;
CacheT &Cache;
typedef GlobalQuarantine<QuarantineCallback, void> QuarantineT;
typedef typename QuarantineT::CacheT QuarantineCacheT;
void initLinkerInitialized() {
// Check if hardware CRC32 is supported in the binary and by the platform,
// if so, opt for the CRC32 hardware version of the checksum.
if (&computeHardwareCRC32 && hasHardwareCRC32())
HashAlgorithm = Checksum::HardwareCRC32;
if (UNLIKELY(!getRandom(&Cookie, sizeof(Cookie))))
Cookie = static_cast<u32>(getMonotonicTime() ^
(reinterpret_cast<uptr>(this) >> 4));
// Store some flags locally.
if (getFlags()->may_return_null)
if (getFlags()->zero_contents)
else if (getFlags()->pattern_fill_contents)
if (getFlags()->dealloc_type_mismatch)
if (getFlags()->delete_size_mismatch)
if (allocatorSupportsMemoryTagging<Params>() &&
QuarantineMaxChunkSize =
const s32 ReleaseToOsIntervalMs = getFlags()->release_to_os_interval_ms;
Secondary.initLinkerInitialized(&Stats, ReleaseToOsIntervalMs);
static_cast<uptr>(getFlags()->quarantine_size_kb << 10),
static_cast<uptr>(getFlags()->thread_local_quarantine_size_kb << 10));
// Initialize the embedded GWP-ASan instance. Requires the main allocator to
// be functional, best called from PostInitCallback.
void initGwpAsan() {
gwp_asan::options::Options Opt;
Opt.Enabled = getFlags()->GWP_ASAN_Enabled;
Opt.MaxSimultaneousAllocations =
Opt.SampleRate = getFlags()->GWP_ASAN_SampleRate;
Opt.InstallSignalHandlers = getFlags()->GWP_ASAN_InstallSignalHandlers;
// Embedded GWP-ASan is locked through the Scudo atfork handler (via
// Allocator::disable calling GWPASan.disable). Disable GWP-ASan's atfork
// handler.
Opt.InstallForkHandlers = false;
Opt.Backtrace = gwp_asan::backtrace::getBacktraceFunction();
if (Opt.InstallSignalHandlers)
&GuardedAlloc, Printf,
#endif // GWP_ASAN_HOOKS
ALWAYS_INLINE void initThreadMaybe(bool MinimalInit = false) {
TSDRegistry.initThreadMaybe(this, MinimalInit);
void reset() { memset(this, 0, sizeof(*this)); }
void unmapTestOnly() {
if (getFlags()->GWP_ASAN_InstallSignalHandlers)
#endif // GWP_ASAN_HOOKS
TSDRegistryT *getTSDRegistry() { return &TSDRegistry; }
// The Cache must be provided zero-initialized.
void initCache(CacheT *Cache) {
Cache->initLinkerInitialized(&Stats, &Primary);
// Release the resources used by a TSD, which involves:
// - draining the local quarantine cache to the global quarantine;
// - releasing the cached pointers back to the Primary;
// - unlinking the local stats from the global ones (destroying the cache does
// the last two items).
void commitBack(TSD<ThisT> *TSD) {
QuarantineCallback(*this, TSD->Cache));
ALWAYS_INLINE void *getHeaderTaggedPointer(void *Ptr) {
if (!allocatorSupportsMemoryTagging<Params>())
return Ptr;
auto UntaggedPtr = untagPointer(Ptr);
if (UntaggedPtr != Ptr)
return UntaggedPtr;
// Secondary, or pointer allocated while memory tagging is unsupported or
// disabled. The tag mismatch is okay in the latter case because tags will
// not be checked.
return addHeaderTag(Ptr);
ALWAYS_INLINE uptr addHeaderTag(uptr Ptr) {
if (!allocatorSupportsMemoryTagging<Params>())
return Ptr;
return addFixedTag(Ptr, 2);
ALWAYS_INLINE void *addHeaderTag(void *Ptr) {
return reinterpret_cast<void *>(addHeaderTag(reinterpret_cast<uptr>(Ptr)));
NOINLINE u32 collectStackTrace() {
// Discard collectStackTrace() frame and allocator function frame.
constexpr uptr DiscardFrames = 2;
uptr Stack[MaxTraceSize + DiscardFrames];
uptr Size =
android_unsafe_frame_pointer_chase(Stack, MaxTraceSize + DiscardFrames);
Size = Min<uptr>(Size, MaxTraceSize + DiscardFrames);
return Depot.insert(Stack + Min<uptr>(DiscardFrames, Size), Stack + Size);
return 0;
uptr computeOddEvenMaskForPointerMaybe(Options Options, uptr Ptr, uptr Size) {
if (!Options.get(OptionBit::UseOddEvenTags))
return 0;
// If a chunk's tag is odd, we want the tags of the surrounding blocks to be
// even, and vice versa. Blocks are laid out Size bytes apart, and adding
// Size to Ptr will flip the least significant set bit of Size in Ptr, so
// that bit will have the pattern 010101... for consecutive blocks, which we
// can use to determine which tag mask to use.
return (Ptr & (1ULL << getLeastSignificantSetBitIndex(Size))) ? 0xaaaa
: 0x5555;
NOINLINE void *allocate(uptr Size, Chunk::Origin Origin,
uptr Alignment = MinAlignment,
bool ZeroContents = false) {
if (UNLIKELY(GuardedAlloc.shouldSample())) {
if (void *Ptr = GuardedAlloc.allocate(roundUpTo(Size, Alignment)))
return Ptr;
#endif // GWP_ASAN_HOOKS
const Options Options = Primary.Options.load();
const FillContentsMode FillContents = ZeroContents ? ZeroFill
: TSDRegistry.getDisableMemInit()
? NoFill
: Options.getFillContentsMode();
if (UNLIKELY(Alignment > MaxAlignment)) {
if (Options.get(OptionBit::MayReturnNull))
return nullptr;
reportAlignmentTooBig(Alignment, MaxAlignment);
if (Alignment < MinAlignment)
Alignment = MinAlignment;
// If the requested size happens to be 0 (more common than you might think),
// allocate MinAlignment bytes on top of the header. Then add the extra
// bytes required to fulfill the alignment requirements: we allocate enough
// to be sure that there will be an address in the block that will satisfy
// the alignment.
const uptr NeededSize =
roundUpTo(Size, MinAlignment) +
((Alignment > MinAlignment) ? Alignment : Chunk::getHeaderSize());
// Takes care of extravagantly large sizes as well as integer overflows.
static_assert(MaxAllowedMallocSize < UINTPTR_MAX - MaxAlignment, "");
if (UNLIKELY(Size >= MaxAllowedMallocSize)) {
if (Options.get(OptionBit::MayReturnNull))
return nullptr;
reportAllocationSizeTooBig(Size, NeededSize, MaxAllowedMallocSize);
DCHECK_LE(Size, NeededSize);
void *Block = nullptr;
uptr ClassId = 0;
uptr SecondaryBlockEnd = 0;
if (LIKELY(PrimaryT::canAllocate(NeededSize))) {
ClassId = SizeClassMap::getClassIdBySize(NeededSize);
DCHECK_NE(ClassId, 0U);
bool UnlockRequired;
auto *TSD = TSDRegistry.getTSDAndLock(&UnlockRequired);
Block = TSD->Cache.allocate(ClassId);
// If the allocation failed, the most likely reason with a 32-bit primary
// is the region being full. In that event, retry in each successively
// larger class until it fits. If it fails to fit in the largest class,
// fallback to the Secondary.
if (UNLIKELY(!Block)) {
while (ClassId < SizeClassMap::LargestClassId && !Block)
Block = TSD->Cache.allocate(++ClassId);
if (!Block)
ClassId = 0;
if (UnlockRequired)
if (UNLIKELY(ClassId == 0))
Block = Secondary.allocate(Options, Size, Alignment, &SecondaryBlockEnd,
if (UNLIKELY(!Block)) {
if (Options.get(OptionBit::MayReturnNull))
return nullptr;
const uptr BlockUptr = reinterpret_cast<uptr>(Block);
const uptr UnalignedUserPtr = BlockUptr + Chunk::getHeaderSize();
const uptr UserPtr = roundUpTo(UnalignedUserPtr, Alignment);
void *Ptr = reinterpret_cast<void *>(UserPtr);
void *TaggedPtr = Ptr;
if (LIKELY(ClassId)) {
// We only need to zero or tag the contents for Primary backed
// allocations. We only set tags for primary allocations in order to avoid
// faulting potentially large numbers of pages for large secondary
// allocations. We assume that guard pages are enough to protect these
// allocations.
// FIXME: When the kernel provides a way to set the background tag of a
// mapping, we should be able to tag secondary allocations as well.
// When memory tagging is enabled, zeroing the contents is done as part of
// setting the tag.
if (UNLIKELY(useMemoryTagging<Params>(Options))) {
uptr PrevUserPtr;
Chunk::UnpackedHeader Header;
const uptr BlockSize = PrimaryT::getSizeByClassId(ClassId);
const uptr BlockEnd = BlockUptr + BlockSize;
// If possible, try to reuse the UAF tag that was set by deallocate().
// For simplicity, only reuse tags if we have the same start address as
// the previous allocation. This handles the majority of cases since
// most allocations will not be more aligned than the minimum alignment.
// We need to handle situations involving reclaimed chunks, and retag
// the reclaimed portions if necessary. In the case where the chunk is
// fully reclaimed, the chunk's header will be zero, which will trigger
// the code path for new mappings and invalid chunks that prepares the
// chunk from scratch. There are three possibilities for partial
// reclaiming:
// (1) Header was reclaimed, data was partially reclaimed.
// (2) Header was not reclaimed, all data was reclaimed (e.g. because
// data started on a page boundary).
// (3) Header was not reclaimed, data was partially reclaimed.
// Case (1) will be handled in the same way as for full reclaiming,
// since the header will be zero.
// We can detect case (2) by loading the tag from the start
// of the chunk. If it is zero, it means that either all data was
// reclaimed (since we never use zero as the chunk tag), or that the
// previous allocation was of size zero. Either way, we need to prepare
// a new chunk from scratch.
// We can detect case (3) by moving to the next page (if covered by the
// chunk) and loading the tag of its first granule. If it is zero, it
// means that all following pages may need to be retagged. On the other
// hand, if it is nonzero, we can assume that all following pages are
// still tagged, according to the logic that if any of the pages
// following the next page were reclaimed, the next page would have been
// reclaimed as well.
uptr TaggedUserPtr;
if (getChunkFromBlock(BlockUptr, &PrevUserPtr, &Header) &&
PrevUserPtr == UserPtr &&
(TaggedUserPtr = loadTag(UserPtr)) != UserPtr) {
uptr PrevEnd = TaggedUserPtr + Header.SizeOrUnusedBytes;
const uptr NextPage = roundUpTo(TaggedUserPtr, getPageSizeCached());
if (NextPage < PrevEnd && loadTag(NextPage) != NextPage)
PrevEnd = NextPage;
TaggedPtr = reinterpret_cast<void *>(TaggedUserPtr);
resizeTaggedChunk(PrevEnd, TaggedUserPtr + Size, BlockEnd);
if (UNLIKELY(FillContents != NoFill && !Header.OriginOrWasZeroed)) {
// If an allocation needs to be zeroed (i.e. calloc) we can normally
// avoid zeroing the memory now since we can rely on memory having
// been zeroed on free, as this is normally done while setting the
// UAF tag. But if tagging was disabled per-thread when the memory
// was freed, it would not have been retagged and thus zeroed, and
// therefore it needs to be zeroed now.
memset(TaggedPtr, 0,
Min(Size, roundUpTo(PrevEnd - TaggedUserPtr,
} else if (Size) {
// Clear any stack metadata that may have previously been stored in
// the chunk data.
memset(TaggedPtr, 0, archMemoryTagGranuleSize());
} else {
const uptr OddEvenMask =
computeOddEvenMaskForPointerMaybe(Options, BlockUptr, BlockSize);
TaggedPtr = prepareTaggedChunk(Ptr, Size, OddEvenMask, BlockEnd);
storePrimaryAllocationStackMaybe(Options, Ptr);
} else {
Block = addHeaderTag(Block);
Ptr = addHeaderTag(Ptr);
if (UNLIKELY(FillContents != NoFill)) {
// This condition is not necessarily unlikely, but since memset is
// costly, we might as well mark it as such.
memset(Block, FillContents == ZeroFill ? 0 : PatternFillByte,
} else {
Block = addHeaderTag(Block);
Ptr = addHeaderTag(Ptr);
if (UNLIKELY(useMemoryTagging<Params>(Options))) {
storeTags(reinterpret_cast<uptr>(Block), reinterpret_cast<uptr>(Ptr));
storeSecondaryAllocationStackMaybe(Options, Ptr, Size);
Chunk::UnpackedHeader Header = {};
if (UNLIKELY(UnalignedUserPtr != UserPtr)) {
const uptr Offset = UserPtr - UnalignedUserPtr;
DCHECK_GE(Offset, 2 * sizeof(u32));
// The BlockMarker has no security purpose, but is specifically meant for
// the chunk iteration function that can be used in debugging situations.
// It is the only situation where we have to locate the start of a chunk
// based on its block address.
reinterpret_cast<u32 *>(Block)[0] = BlockMarker;
reinterpret_cast<u32 *>(Block)[1] = static_cast<u32>(Offset);
Header.Offset = (Offset >> MinAlignmentLog) & Chunk::OffsetMask;
Header.ClassId = ClassId & Chunk::ClassIdMask;
Header.State = Chunk::State::Allocated;
Header.OriginOrWasZeroed = Origin & Chunk::OriginMask;
Header.SizeOrUnusedBytes =
(ClassId ? Size : SecondaryBlockEnd - (UserPtr + Size)) &
Chunk::storeHeader(Cookie, Ptr, &Header);
if (UNLIKELY(&__scudo_allocate_hook))
__scudo_allocate_hook(TaggedPtr, Size);
return TaggedPtr;
NOINLINE void deallocate(void *Ptr, Chunk::Origin Origin, uptr DeleteSize = 0,
UNUSED uptr Alignment = MinAlignment) {
// For a deallocation, we only ensure minimal initialization, meaning thread
// local data will be left uninitialized for now (when using ELF TLS). The
// fallback cache will be used instead. This is a workaround for a situation
// where the only heap operation performed in a thread would be a free past
// the TLS destructors, ending up in initialized thread specific data never
// being destroyed properly. Any other heap operation will do a full init.
if (UNLIKELY(GuardedAlloc.pointerIsMine(Ptr))) {
#endif // GWP_ASAN_HOOKS
if (UNLIKELY(&__scudo_deallocate_hook))
if (UNLIKELY(!Ptr))
if (UNLIKELY(!isAligned(reinterpret_cast<uptr>(Ptr), MinAlignment)))
reportMisalignedPointer(AllocatorAction::Deallocating, Ptr);
Ptr = getHeaderTaggedPointer(Ptr);
Chunk::UnpackedHeader Header;
Chunk::loadHeader(Cookie, Ptr, &Header);
if (UNLIKELY(Header.State != Chunk::State::Allocated))
reportInvalidChunkState(AllocatorAction::Deallocating, Ptr);
const Options Options = Primary.Options.load();
if (Options.get(OptionBit::DeallocTypeMismatch)) {
if (UNLIKELY(Header.OriginOrWasZeroed != Origin)) {
// With the exception of memalign'd chunks, that can be still be free'd.
if (Header.OriginOrWasZeroed != Chunk::Origin::Memalign ||
Origin != Chunk::Origin::Malloc)
reportDeallocTypeMismatch(AllocatorAction::Deallocating, Ptr,
Header.OriginOrWasZeroed, Origin);
const uptr Size = getSize(Ptr, &Header);
if (DeleteSize && Options.get(OptionBit::DeleteSizeMismatch)) {
if (UNLIKELY(DeleteSize != Size))
reportDeleteSizeMismatch(Ptr, DeleteSize, Size);
quarantineOrDeallocateChunk(Options, Ptr, &Header, Size);
void *reallocate(void *OldPtr, uptr NewSize, uptr Alignment = MinAlignment) {
const Options Options = Primary.Options.load();
if (UNLIKELY(NewSize >= MaxAllowedMallocSize)) {
if (Options.get(OptionBit::MayReturnNull))
return nullptr;
reportAllocationSizeTooBig(NewSize, 0, MaxAllowedMallocSize);
void *OldTaggedPtr = OldPtr;
OldPtr = getHeaderTaggedPointer(OldPtr);
// The following cases are handled by the C wrappers.
DCHECK_NE(OldPtr, nullptr);
DCHECK_NE(NewSize, 0);
if (UNLIKELY(GuardedAlloc.pointerIsMine(OldPtr))) {
uptr OldSize = GuardedAlloc.getSize(OldPtr);
void *NewPtr = allocate(NewSize, Chunk::Origin::Malloc, Alignment);
if (NewPtr)
memcpy(NewPtr, OldPtr, (NewSize < OldSize) ? NewSize : OldSize);
return NewPtr;
#endif // GWP_ASAN_HOOKS
if (UNLIKELY(!isAligned(reinterpret_cast<uptr>(OldPtr), MinAlignment)))
reportMisalignedPointer(AllocatorAction::Reallocating, OldPtr);
Chunk::UnpackedHeader OldHeader;
Chunk::loadHeader(Cookie, OldPtr, &OldHeader);
if (UNLIKELY(OldHeader.State != Chunk::State::Allocated))
reportInvalidChunkState(AllocatorAction::Reallocating, OldPtr);
// Pointer has to be allocated with a malloc-type function. Some
// applications think that it is OK to realloc a memalign'ed pointer, which
// will trigger this check. It really isn't.
if (Options.get(OptionBit::DeallocTypeMismatch)) {
if (UNLIKELY(OldHeader.OriginOrWasZeroed != Chunk::Origin::Malloc))
reportDeallocTypeMismatch(AllocatorAction::Reallocating, OldPtr,
void *BlockBegin = getBlockBegin(OldTaggedPtr, &OldHeader);
uptr BlockEnd;
uptr OldSize;
const uptr ClassId = OldHeader.ClassId;
if (LIKELY(ClassId)) {
BlockEnd = reinterpret_cast<uptr>(BlockBegin) +
OldSize = OldHeader.SizeOrUnusedBytes;
} else {
BlockEnd = SecondaryT::getBlockEnd(BlockBegin);
OldSize = BlockEnd - (reinterpret_cast<uptr>(OldTaggedPtr) +
// If the new chunk still fits in the previously allocated block (with a
// reasonable delta), we just keep the old block, and update the chunk
// header to reflect the size change.
if (reinterpret_cast<uptr>(OldTaggedPtr) + NewSize <= BlockEnd) {
if (NewSize > OldSize || (OldSize - NewSize) < getPageSizeCached()) {
Chunk::UnpackedHeader NewHeader = OldHeader;
NewHeader.SizeOrUnusedBytes =
(ClassId ? NewSize
: BlockEnd -
(reinterpret_cast<uptr>(OldTaggedPtr) + NewSize)) &
Chunk::compareExchangeHeader(Cookie, OldPtr, &NewHeader, &OldHeader);
if (UNLIKELY(useMemoryTagging<Params>(Options))) {
if (ClassId) {
resizeTaggedChunk(reinterpret_cast<uptr>(OldTaggedPtr) + OldSize,
reinterpret_cast<uptr>(OldTaggedPtr) + NewSize,
storePrimaryAllocationStackMaybe(Options, OldPtr);
} else {
storeSecondaryAllocationStackMaybe(Options, OldPtr, NewSize);
return OldTaggedPtr;
// Otherwise we allocate a new one, and deallocate the old one. Some
// allocators will allocate an even larger chunk (by a fixed factor) to
// allow for potential further in-place realloc. The gains of such a trick
// are currently unclear.
void *NewPtr = allocate(NewSize, Chunk::Origin::Malloc, Alignment);
if (LIKELY(NewPtr)) {
memcpy(NewPtr, OldTaggedPtr, Min(NewSize, OldSize));
quarantineOrDeallocateChunk(Options, OldPtr, &OldHeader, OldSize);
return NewPtr;
// TODO(kostyak): disable() is currently best-effort. There are some small
// windows of time when an allocation could still succeed after
// this function finishes. We will revisit that later.
void disable() {
void enable() {
// The function returns the amount of bytes required to store the statistics,
// which might be larger than the amount of bytes provided. Note that the
// statistics buffer is not necessarily constant between calls to this
// function. This can be called with a null buffer or zero size for buffer
// sizing purposes.
uptr getStats(char *Buffer, uptr Size) {
ScopedString Str(1024);
const uptr Length = getStats(&Str) + 1;
if (Length < Size)
Size = Length;
if (Buffer && Size) {
memcpy(Buffer,, Size);
Buffer[Size - 1] = '\0';
return Length;
void printStats() {
ScopedString Str(1024);
void releaseToOS() {
// Iterate over all chunks and call a callback for all busy chunks located
// within the provided memory range. Said callback must not use this allocator
// or a deadlock can ensue. This fits Android's malloc_iterate() needs.
void iterateOverChunks(uptr Base, uptr Size, iterate_callback Callback,
void *Arg) {
const uptr From = Base;
const uptr To = Base + Size;
bool MayHaveTaggedPrimary = allocatorSupportsMemoryTagging<Params>() &&
auto Lambda = [this, From, To, MayHaveTaggedPrimary, Callback,
Arg](uptr Block) {
if (Block < From || Block >= To)
uptr Chunk;
Chunk::UnpackedHeader Header;
if (MayHaveTaggedPrimary) {
// A chunk header can either have a zero tag (tagged primary) or the
// header tag (secondary, or untagged primary). We don't know which so
// try both.
ScopedDisableMemoryTagChecks x;
if (!getChunkFromBlock(Block, &Chunk, &Header) &&
!getChunkFromBlock(addHeaderTag(Block), &Chunk, &Header))
} else {
if (!getChunkFromBlock(addHeaderTag(Block), &Chunk, &Header))
if (Header.State == Chunk::State::Allocated) {
uptr TaggedChunk = Chunk;
if (allocatorSupportsMemoryTagging<Params>())
TaggedChunk = untagPointer(TaggedChunk);
if (useMemoryTagging<Params>(Primary.Options.load()))
TaggedChunk = loadTag(Chunk);
Callback(TaggedChunk, getSize(reinterpret_cast<void *>(Chunk), &Header),
GuardedAlloc.iterate(reinterpret_cast<void *>(Base), Size, Callback, Arg);
bool canReturnNull() {
return Primary.Options.load().get(OptionBit::MayReturnNull);
bool setOption(Option O, sptr Value) {
if (O == Option::MemtagTuning) {
// Enabling odd/even tags involves a tradeoff between use-after-free
// detection and buffer overflow detection. Odd/even tags make it more
// likely for buffer overflows to be detected by increasing the size of
// the guaranteed "red zone" around the allocation, but on the other hand
// use-after-free is less likely to be detected because the tag space for
// any particular chunk is cut in half. Therefore we use this tuning
// setting to control whether odd/even tags are enabled.
else if (Value == M_MEMTAG_TUNING_UAF)
return true;
} else {
// We leave it to the various sub-components to decide whether or not they
// want to handle the option, but we do not want to short-circuit
// execution if one of the setOption was to return false.
const bool PrimaryResult = Primary.setOption(O, Value);
const bool SecondaryResult = Secondary.setOption(O, Value);
const bool RegistryResult = TSDRegistry.setOption(O, Value);
return PrimaryResult && SecondaryResult && RegistryResult;
return false;
// Return the usable size for a given chunk. Technically we lie, as we just
// report the actual size of a chunk. This is done to counteract code actively
// writing past the end of a chunk (like sqlite3) when the usable size allows
// for it, which then forces realloc to copy the usable size of a chunk as
// opposed to its actual size.
uptr getUsableSize(const void *Ptr) {
if (UNLIKELY(!Ptr))
return 0;
if (UNLIKELY(GuardedAlloc.pointerIsMine(Ptr)))
return GuardedAlloc.getSize(Ptr);
#endif // GWP_ASAN_HOOKS
Ptr = getHeaderTaggedPointer(const_cast<void *>(Ptr));
Chunk::UnpackedHeader Header;
Chunk::loadHeader(Cookie, Ptr, &Header);
// Getting the usable size of a chunk only makes sense if it's allocated.
if (UNLIKELY(Header.State != Chunk::State::Allocated))
reportInvalidChunkState(AllocatorAction::Sizing, const_cast<void *>(Ptr));
return getSize(Ptr, &Header);
void getStats(StatCounters S) {
// Returns true if the pointer provided was allocated by the current
// allocator instance, which is compliant with tcmalloc's ownership concept.
// A corrupted chunk will not be reported as owned, which is WAI.
bool isOwned(const void *Ptr) {
if (GuardedAlloc.pointerIsMine(Ptr))
return true;
#endif // GWP_ASAN_HOOKS
if (!Ptr || !isAligned(reinterpret_cast<uptr>(Ptr), MinAlignment))
return false;
Ptr = getHeaderTaggedPointer(const_cast<void *>(Ptr));
Chunk::UnpackedHeader Header;
return Chunk::isValid(Cookie, Ptr, &Header) &&
Header.State == Chunk::State::Allocated;
bool useMemoryTaggingTestOnly() const {
return useMemoryTagging<Params>(Primary.Options.load());
void disableMemoryTagging() {
// If we haven't been initialized yet, we need to initialize now in order to
// prevent a future call to initThreadMaybe() from enabling memory tagging
// based on feature detection. But don't call initThreadMaybe() because it
// may end up calling the allocator (via pthread_atfork, via the post-init
// callback), which may cause mappings to be created with memory tagging
// enabled.
if (allocatorSupportsMemoryTagging<Params>()) {
void setTrackAllocationStacks(bool Track) {
if (Track)
void setFillContents(FillContentsMode FillContents) {
void setAddLargeAllocationSlack(bool AddSlack) {
if (AddSlack)
const char *getStackDepotAddress() const {
return reinterpret_cast<const char *>(&Depot);
const char *getRegionInfoArrayAddress() const {
return Primary.getRegionInfoArrayAddress();
static uptr getRegionInfoArraySize() {
return PrimaryT::getRegionInfoArraySize();
const char *getRingBufferAddress() const {
return reinterpret_cast<const char *>(&RingBuffer);
static uptr getRingBufferSize() { return sizeof(RingBuffer); }
static const uptr MaxTraceSize = 64;
static void collectTraceMaybe(const StackDepot *Depot,
uintptr_t (&Trace)[MaxTraceSize], u32 Hash) {
uptr RingPos, Size;
if (!Depot->find(Hash, &RingPos, &Size))
for (unsigned I = 0; I != Size && I != MaxTraceSize; ++I)
Trace[I] = (*Depot)[RingPos + I];
static void getErrorInfo(struct scudo_error_info *ErrorInfo,
uintptr_t FaultAddr, const char *DepotPtr,
const char *RegionInfoPtr, const char *RingBufferPtr,
const char *Memory, const char *MemoryTags,
uintptr_t MemoryAddr, size_t MemorySize) {
*ErrorInfo = {};
if (!allocatorSupportsMemoryTagging<Params>() ||
MemoryAddr + MemorySize < MemoryAddr)
auto *Depot = reinterpret_cast<const StackDepot *>(DepotPtr);
size_t NextErrorReport = 0;
if (extractTag(FaultAddr) != 0)
getInlineErrorInfo(ErrorInfo, NextErrorReport, FaultAddr, Depot,
RegionInfoPtr, Memory, MemoryTags, MemoryAddr,
getRingBufferErrorInfo(ErrorInfo, NextErrorReport, FaultAddr, Depot,
using SecondaryT = MapAllocator<Params>;
typedef typename PrimaryT::SizeClassMap SizeClassMap;
static const uptr MinAlignmentLog = SCUDO_MIN_ALIGNMENT_LOG;
static const uptr MaxAlignmentLog = 24U; // 16 MB seems reasonable.
static const uptr MinAlignment = 1UL << MinAlignmentLog;
static const uptr MaxAlignment = 1UL << MaxAlignmentLog;
static const uptr MaxAllowedMallocSize =
FIRST_32_SECOND_64(1UL << 31, 1ULL << 40);
static_assert(MinAlignment >= sizeof(Chunk::PackedHeader),
"Minimal alignment must at least cover a chunk header.");
static_assert(!allocatorSupportsMemoryTagging<Params>() ||
MinAlignment >= archMemoryTagGranuleSize(),
static const u32 BlockMarker = 0x44554353U;
// These are indexes into an "array" of 32-bit values that store information
// inline with a chunk that is relevant to diagnosing memory tag faults, where
// 0 corresponds to the address of the user memory. This means that only
// negative indexes may be used. The smallest index that may be used is -2,
// which corresponds to 8 bytes before the user memory, because the chunk
// header size is 8 bytes and in allocators that support memory tagging the
// minimum alignment is at least the tag granule size (16 on aarch64).
static const sptr MemTagAllocationTraceIndex = -2;
static const sptr MemTagAllocationTidIndex = -1;
u32 Cookie;
u32 QuarantineMaxChunkSize;
GlobalStats Stats;
PrimaryT Primary;
SecondaryT Secondary;
QuarantineT Quarantine;
TSDRegistryT TSDRegistry;
gwp_asan::GuardedPoolAllocator GuardedAlloc;
#endif // GWP_ASAN_HOOKS
StackDepot Depot;
struct AllocationRingBuffer {
struct Entry {
atomic_uptr Ptr;
atomic_uptr AllocationSize;
atomic_u32 AllocationTrace;
atomic_u32 AllocationTid;
atomic_u32 DeallocationTrace;
atomic_u32 DeallocationTid;
atomic_uptr Pos;
static const uptr NumEntries = 2;
static const uptr NumEntries = 32768;
Entry Entries[NumEntries];
AllocationRingBuffer RingBuffer;
// The following might get optimized out by the compiler.
NOINLINE void performSanityChecks() {
// Verify that the header offset field can hold the maximum offset. In the
// case of the Secondary allocator, it takes care of alignment and the
// offset will always be small. In the case of the Primary, the worst case
// scenario happens in the last size class, when the backend allocation
// would already be aligned on the requested alignment, which would happen
// to be the maximum alignment that would fit in that size class. As a
// result, the maximum offset will be at most the maximum alignment for the
// last size class minus the header size, in multiples of MinAlignment.
Chunk::UnpackedHeader Header = {};
const uptr MaxPrimaryAlignment = 1UL << getMostSignificantSetBitIndex(
SizeClassMap::MaxSize - MinAlignment);
const uptr MaxOffset =
(MaxPrimaryAlignment - Chunk::getHeaderSize()) >> MinAlignmentLog;
Header.Offset = MaxOffset & Chunk::OffsetMask;
if (UNLIKELY(Header.Offset != MaxOffset))
// Verify that we can fit the maximum size or amount of unused bytes in the
// header. Given that the Secondary fits the allocation to a page, the worst
// case scenario happens in the Primary. It will depend on the second to
// last and last class sizes, as well as the dynamic base for the Primary.
// The following is an over-approximation that works for our needs.
const uptr MaxSizeOrUnusedBytes = SizeClassMap::MaxSize - 1;
Header.SizeOrUnusedBytes = MaxSizeOrUnusedBytes;
if (UNLIKELY(Header.SizeOrUnusedBytes != MaxSizeOrUnusedBytes))
reportSanityCheckError("size (or unused bytes)");
const uptr LargestClassId = SizeClassMap::LargestClassId;
Header.ClassId = LargestClassId;
if (UNLIKELY(Header.ClassId != LargestClassId))
reportSanityCheckError("class ID");
static inline void *getBlockBegin(const void *Ptr,
Chunk::UnpackedHeader *Header) {
return reinterpret_cast<void *>(
reinterpret_cast<uptr>(Ptr) - Chunk::getHeaderSize() -
(static_cast<uptr>(Header->Offset) << MinAlignmentLog));
// Return the size of a chunk as requested during its allocation.
inline uptr getSize(const void *Ptr, Chunk::UnpackedHeader *Header) {
const uptr SizeOrUnusedBytes = Header->SizeOrUnusedBytes;
if (LIKELY(Header->ClassId))
return SizeOrUnusedBytes;
if (allocatorSupportsMemoryTagging<Params>())
Ptr = untagPointer(const_cast<void *>(Ptr));
return SecondaryT::getBlockEnd(getBlockBegin(Ptr, Header)) -
reinterpret_cast<uptr>(Ptr) - SizeOrUnusedBytes;
void quarantineOrDeallocateChunk(Options Options, void *Ptr,
Chunk::UnpackedHeader *Header, uptr Size) {
Chunk::UnpackedHeader NewHeader = *Header;
if (UNLIKELY(useMemoryTagging<Params>(Options))) {
u8 PrevTag = 0;
if (NewHeader.ClassId) {
PrevTag = extractTag(loadTag(reinterpret_cast<uptr>(Ptr)));
if (!TSDRegistry.getDisableMemInit()) {
uptr TaggedBegin, TaggedEnd;
const uptr OddEvenMask = computeOddEvenMaskForPointerMaybe(
Options, reinterpret_cast<uptr>(getBlockBegin(Ptr, &NewHeader)),
// Exclude the previous tag so that immediate use after free is
// detected 100% of the time.
setRandomTag(Ptr, Size, OddEvenMask | (1UL << PrevTag), &TaggedBegin,
NewHeader.OriginOrWasZeroed = !TSDRegistry.getDisableMemInit();
storeDeallocationStackMaybe(Options, Ptr, PrevTag, Size);
// If the quarantine is disabled, the actual size of a chunk is 0 or larger
// than the maximum allowed, we return a chunk directly to the backend.
// This purposefully underflows for Size == 0.
const bool BypassQuarantine = !Quarantine.getCacheSize() ||
((Size - 1) >= QuarantineMaxChunkSize) ||
if (BypassQuarantine) {
NewHeader.State = Chunk::State::Available;
Chunk::compareExchangeHeader(Cookie, Ptr, &NewHeader, Header);
if (allocatorSupportsMemoryTagging<Params>())
Ptr = untagPointer(Ptr);
void *BlockBegin = getBlockBegin(Ptr, &NewHeader);
const uptr ClassId = NewHeader.ClassId;
if (LIKELY(ClassId)) {
bool UnlockRequired;
auto *TSD = TSDRegistry.getTSDAndLock(&UnlockRequired);
TSD->Cache.deallocate(ClassId, BlockBegin);
if (UnlockRequired)
} else {
if (UNLIKELY(useMemoryTagging<Params>(Options)))
Secondary.deallocate(Options, BlockBegin);
} else {
NewHeader.State = Chunk::State::Quarantined;
Chunk::compareExchangeHeader(Cookie, Ptr, &NewHeader, Header);
bool UnlockRequired;
auto *TSD = TSDRegistry.getTSDAndLock(&UnlockRequired);
QuarantineCallback(*this, TSD->Cache), Ptr, Size);
if (UnlockRequired)
bool getChunkFromBlock(uptr Block, uptr *Chunk,
Chunk::UnpackedHeader *Header) {
*Chunk =
Block + getChunkOffsetFromBlock(reinterpret_cast<const char *>(Block));
return Chunk::isValid(Cookie, reinterpret_cast<void *>(*Chunk), Header);
static uptr getChunkOffsetFromBlock(const char *Block) {
u32 Offset = 0;
if (reinterpret_cast<const u32 *>(Block)[0] == BlockMarker)
Offset = reinterpret_cast<const u32 *>(Block)[1];
return Offset + Chunk::getHeaderSize();
void storePrimaryAllocationStackMaybe(Options Options, void *Ptr) {
if (!UNLIKELY(Options.get(OptionBit::TrackAllocationStacks)))
auto *Ptr32 = reinterpret_cast<u32 *>(Ptr);
Ptr32[MemTagAllocationTraceIndex] = collectStackTrace();
Ptr32[MemTagAllocationTidIndex] = getThreadID();
void storeRingBufferEntry(void *Ptr, u32 AllocationTrace, u32 AllocationTid,
uptr AllocationSize, u32 DeallocationTrace,
u32 DeallocationTid) {
uptr Pos = atomic_fetch_add(&RingBuffer.Pos, 1, memory_order_relaxed);
typename AllocationRingBuffer::Entry *Entry =
&RingBuffer.Entries[Pos % AllocationRingBuffer::NumEntries];
// First invalidate our entry so that we don't attempt to interpret a
// partially written state in getSecondaryErrorInfo(). The fences below
// ensure that the compiler does not move the stores to Ptr in between the
// stores to the other fields.
atomic_store_relaxed(&Entry->Ptr, 0);
atomic_store_relaxed(&Entry->AllocationTrace, AllocationTrace);
atomic_store_relaxed(&Entry->AllocationTid, AllocationTid);
atomic_store_relaxed(&Entry->AllocationSize, AllocationSize);
atomic_store_relaxed(&Entry->DeallocationTrace, DeallocationTrace);
atomic_store_relaxed(&Entry->DeallocationTid, DeallocationTid);
atomic_store_relaxed(&Entry->Ptr, reinterpret_cast<uptr>(Ptr));
void storeSecondaryAllocationStackMaybe(Options Options, void *Ptr,
uptr Size) {
if (!UNLIKELY(Options.get(OptionBit::TrackAllocationStacks)))
u32 Trace = collectStackTrace();
u32 Tid = getThreadID();
auto *Ptr32 = reinterpret_cast<u32 *>(Ptr);
Ptr32[MemTagAllocationTraceIndex] = Trace;
Ptr32[MemTagAllocationTidIndex] = Tid;
storeRingBufferEntry(untagPointer(Ptr), Trace, Tid, Size, 0, 0);
void storeDeallocationStackMaybe(Options Options, void *Ptr, u8 PrevTag,
uptr Size) {
if (!UNLIKELY(Options.get(OptionBit::TrackAllocationStacks)))
auto *Ptr32 = reinterpret_cast<u32 *>(Ptr);
u32 AllocationTrace = Ptr32[MemTagAllocationTraceIndex];
u32 AllocationTid = Ptr32[MemTagAllocationTidIndex];
u32 DeallocationTrace = collectStackTrace();
u32 DeallocationTid = getThreadID();
storeRingBufferEntry(addFixedTag(untagPointer(Ptr), PrevTag),
AllocationTrace, AllocationTid, Size,
DeallocationTrace, DeallocationTid);
static const size_t NumErrorReports =
sizeof(((scudo_error_info *)0)->reports) /
sizeof(((scudo_error_info *)0)->reports[0]);
static void getInlineErrorInfo(struct scudo_error_info *ErrorInfo,
size_t &NextErrorReport, uintptr_t FaultAddr,
const StackDepot *Depot,
const char *RegionInfoPtr, const char *Memory,
const char *MemoryTags, uintptr_t MemoryAddr,
size_t MemorySize) {
uptr UntaggedFaultAddr = untagPointer(FaultAddr);
u8 FaultAddrTag = extractTag(FaultAddr);
BlockInfo Info =
PrimaryT::findNearestBlock(RegionInfoPtr, UntaggedFaultAddr);
auto GetGranule = [&](uptr Addr, const char **Data, uint8_t *Tag) -> bool {
if (Addr < MemoryAddr || Addr + archMemoryTagGranuleSize() < Addr ||
Addr + archMemoryTagGranuleSize() > MemoryAddr + MemorySize)
return false;
*Data = &Memory[Addr - MemoryAddr];
*Tag = static_cast<u8>(
MemoryTags[(Addr - MemoryAddr) / archMemoryTagGranuleSize()]);
return true;
auto ReadBlock = [&](uptr Addr, uptr *ChunkAddr,
Chunk::UnpackedHeader *Header, const u32 **Data,
u8 *Tag) {
const char *BlockBegin;
u8 BlockBeginTag;
if (!GetGranule(Addr, &BlockBegin, &BlockBeginTag))
return false;
uptr ChunkOffset = getChunkOffsetFromBlock(BlockBegin);
*ChunkAddr = Addr + ChunkOffset;
const char *ChunkBegin;
if (!GetGranule(*ChunkAddr, &ChunkBegin, Tag))
return false;
*Header = *reinterpret_cast<const Chunk::UnpackedHeader *>(
ChunkBegin - Chunk::getHeaderSize());
*Data = reinterpret_cast<const u32 *>(ChunkBegin);
return true;
if (NextErrorReport == NumErrorReports)
auto CheckOOB = [&](uptr BlockAddr) {
if (BlockAddr < Info.RegionBegin || BlockAddr >= Info.RegionEnd)
return false;
uptr ChunkAddr;
Chunk::UnpackedHeader Header;
const u32 *Data;
uint8_t Tag;
if (!ReadBlock(BlockAddr, &ChunkAddr, &Header, &Data, &Tag) ||
Header.State != Chunk::State::Allocated || Tag != FaultAddrTag)
return false;
auto *R = &ErrorInfo->reports[NextErrorReport++];
R->error_type =
R->allocation_address = ChunkAddr;
R->allocation_size = Header.SizeOrUnusedBytes;
collectTraceMaybe(Depot, R->allocation_trace,
R->allocation_tid = Data[MemTagAllocationTidIndex];
return NextErrorReport == NumErrorReports;
if (CheckOOB(Info.BlockBegin))
// Check for OOB in the 30 surrounding blocks. Beyond that we are likely to
// hit false positives.
for (int I = 1; I != 16; ++I)
if (CheckOOB(Info.BlockBegin + I * Info.BlockSize) ||
CheckOOB(Info.BlockBegin - I * Info.BlockSize))
static void getRingBufferErrorInfo(struct scudo_error_info *ErrorInfo,
size_t &NextErrorReport,
uintptr_t FaultAddr,
const StackDepot *Depot,
const char *RingBufferPtr) {
auto *RingBuffer =
reinterpret_cast<const AllocationRingBuffer *>(RingBufferPtr);
uptr Pos = atomic_load_relaxed(&RingBuffer->Pos);
for (uptr I = Pos - 1; I != Pos - 1 - AllocationRingBuffer::NumEntries &&
NextErrorReport != NumErrorReports;
--I) {
auto *Entry = &RingBuffer->Entries[I % AllocationRingBuffer::NumEntries];
uptr EntryPtr = atomic_load_relaxed(&Entry->Ptr);
uptr UntaggedEntryPtr = untagPointer(EntryPtr);
uptr EntrySize = atomic_load_relaxed(&Entry->AllocationSize);
if (!EntryPtr || FaultAddr < EntryPtr - getPageSizeCached() ||
FaultAddr >= EntryPtr + EntrySize + getPageSizeCached())
u32 AllocationTrace = atomic_load_relaxed(&Entry->AllocationTrace);
u32 AllocationTid = atomic_load_relaxed(&Entry->AllocationTid);
u32 DeallocationTrace = atomic_load_relaxed(&Entry->DeallocationTrace);
u32 DeallocationTid = atomic_load_relaxed(&Entry->DeallocationTid);
// For UAF the ring buffer will contain two entries, one for the
// allocation and another for the deallocation. Don't report buffer
// overflow/underflow using the allocation entry if we have already
// collected a report from the deallocation entry.
if (!DeallocationTrace) {
bool Found = false;
for (uptr J = 0; J != NextErrorReport; ++J) {
if (ErrorInfo->reports[J].allocation_address == UntaggedEntryPtr) {
Found = true;
if (Found)
auto *R = &ErrorInfo->reports[NextErrorReport++];
if (DeallocationTid)
R->error_type = USE_AFTER_FREE;
else if (FaultAddr < EntryPtr)
R->error_type = BUFFER_UNDERFLOW;
R->error_type = BUFFER_OVERFLOW;
R->allocation_address = UntaggedEntryPtr;
R->allocation_size = EntrySize;
collectTraceMaybe(Depot, R->allocation_trace, AllocationTrace);
R->allocation_tid = AllocationTid;
collectTraceMaybe(Depot, R->deallocation_trace, DeallocationTrace);
R->deallocation_tid = DeallocationTid;
uptr getStats(ScopedString *Str) {
return Str->length();
} // namespace scudo