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-rw-r--r--lib/scudo/scudo_allocator.cpp16
-rw-r--r--lib/scudo/scudo_tls.h2
-rw-r--r--lib/scudo/scudo_utils.cpp36
-rw-r--r--lib/scudo/scudo_utils.h57
4 files changed, 55 insertions, 56 deletions
diff --git a/lib/scudo/scudo_allocator.cpp b/lib/scudo/scudo_allocator.cpp
index 00fa19218..ec9132f90 100644
--- a/lib/scudo/scudo_allocator.cpp
+++ b/lib/scudo/scudo_allocator.cpp
@@ -264,7 +264,7 @@ ScudoQuarantineCache *getQuarantineCache(ScudoThreadContext *ThreadContext) {
ScudoQuarantineCache *>(ThreadContext->QuarantineCachePlaceHolder);
}
-Xorshift128Plus *getPrng(ScudoThreadContext *ThreadContext) {
+ScudoPrng *getPrng(ScudoThreadContext *ThreadContext) {
return &ThreadContext->Prng;
}
@@ -283,7 +283,7 @@ struct ScudoAllocator {
StaticSpinMutex FallbackMutex;
AllocatorCache FallbackAllocatorCache;
ScudoQuarantineCache FallbackQuarantineCache;
- Xorshift128Plus FallbackPrng;
+ ScudoPrng FallbackPrng;
bool DeallocationTypeMismatch;
bool ZeroContents;
@@ -333,8 +333,8 @@ struct ScudoAllocator {
static_cast<uptr>(Options.QuarantineSizeMb) << 20,
static_cast<uptr>(Options.ThreadLocalQuarantineSizeKb) << 10);
BackendAllocator.InitCache(&FallbackAllocatorCache);
- FallbackPrng.initFromURandom();
- Cookie = FallbackPrng.getNext();
+ FallbackPrng.init();
+ Cookie = FallbackPrng.getU64();
}
// Helper function that checks for a valid Scudo chunk. nullptr isn't.
@@ -373,19 +373,19 @@ struct ScudoAllocator {
bool FromPrimary = PrimaryAllocator::CanAllocate(AlignedSize, MinAlignment);
void *Ptr;
- uptr Salt;
+ u8 Salt;
uptr AllocationSize = FromPrimary ? AlignedSize : NeededSize;
uptr AllocationAlignment = FromPrimary ? MinAlignment : Alignment;
ScudoThreadContext *ThreadContext = getThreadContextAndLock();
if (LIKELY(ThreadContext)) {
- Salt = getPrng(ThreadContext)->getNext();
+ Salt = getPrng(ThreadContext)->getU8();
Ptr = BackendAllocator.Allocate(getAllocatorCache(ThreadContext),
AllocationSize, AllocationAlignment,
FromPrimary);
ThreadContext->unlock();
} else {
SpinMutexLock l(&FallbackMutex);
- Salt = FallbackPrng.getNext();
+ Salt = FallbackPrng.getU8();
Ptr = BackendAllocator.Allocate(&FallbackAllocatorCache, AllocationSize,
AllocationAlignment, FromPrimary);
}
@@ -612,7 +612,7 @@ static void initScudoInternal(const AllocatorOptions &Options) {
void ScudoThreadContext::init() {
getBackendAllocator().InitCache(&Cache);
- Prng.initFromURandom();
+ Prng.init();
memset(QuarantineCachePlaceHolder, 0, sizeof(QuarantineCachePlaceHolder));
}
diff --git a/lib/scudo/scudo_tls.h b/lib/scudo/scudo_tls.h
index f6039bebe..20c49204c 100644
--- a/lib/scudo/scudo_tls.h
+++ b/lib/scudo/scudo_tls.h
@@ -30,7 +30,7 @@ namespace __scudo {
struct ALIGNED(64) ScudoThreadContext : public ScudoThreadContextPlatform {
AllocatorCache Cache;
- Xorshift128Plus Prng;
+ ScudoPrng Prng;
uptr QuarantineCachePlaceHolder[4];
void init();
void commitBack();
diff --git a/lib/scudo/scudo_utils.cpp b/lib/scudo/scudo_utils.cpp
index 31c391946..f7903ff34 100644
--- a/lib/scudo/scudo_utils.cpp
+++ b/lib/scudo/scudo_utils.cpp
@@ -123,40 +123,4 @@ bool testCPUFeature(CPUFeature Feature) {
}
#endif // defined(__x86_64__) || defined(__i386__)
-// readRetry will attempt to read Count bytes from the Fd specified, and if
-// interrupted will retry to read additional bytes to reach Count.
-static ssize_t readRetry(int Fd, u8 *Buffer, size_t Count) {
- ssize_t AmountRead = 0;
- while (static_cast<size_t>(AmountRead) < Count) {
- ssize_t Result = read(Fd, Buffer + AmountRead, Count - AmountRead);
- if (Result > 0)
- AmountRead += Result;
- else if (!Result)
- break;
- else if (errno != EINTR) {
- AmountRead = -1;
- break;
- }
- }
- return AmountRead;
-}
-
-static void fillRandom(u8 *Data, ssize_t Size) {
- int Fd = open("/dev/urandom", O_RDONLY);
- if (Fd < 0) {
- dieWithMessage("ERROR: failed to open /dev/urandom.\n");
- }
- bool Success = readRetry(Fd, Data, Size) == Size;
- close(Fd);
- if (!Success) {
- dieWithMessage("ERROR: failed to read enough data from /dev/urandom.\n");
- }
-}
-
-// Seeds the xorshift state with /dev/urandom.
-// TODO(kostyak): investigate using getrandom() if available.
-void Xorshift128Plus::initFromURandom() {
- fillRandom(reinterpret_cast<u8 *>(State), sizeof(State));
-}
-
} // namespace __scudo
diff --git a/lib/scudo/scudo_utils.h b/lib/scudo/scudo_utils.h
index 7198476f4..6c6c9d893 100644
--- a/lib/scudo/scudo_utils.h
+++ b/lib/scudo/scudo_utils.h
@@ -36,23 +36,58 @@ enum CPUFeature {
};
bool testCPUFeature(CPUFeature feature);
-// Tiny PRNG based on https://en.wikipedia.org/wiki/Xorshift#xorshift.2B
-// The state (128 bits) will be stored in thread local storage.
-struct Xorshift128Plus {
+INLINE u64 rotl(const u64 X, int K) {
+ return (X << K) | (X >> (64 - K));
+}
+
+// XoRoShiRo128+ PRNG (http://xoroshiro.di.unimi.it/).
+struct XoRoShiRo128Plus {
public:
- void initFromURandom();
- u64 getNext() {
- u64 x = State[0];
- const u64 y = State[1];
- State[0] = y;
- x ^= x << 23;
- State[1] = x ^ y ^ (x >> 17) ^ (y >> 26);
- return State[1] + y;
+ void init() {
+ if (UNLIKELY(!GetRandom(reinterpret_cast<void *>(State), sizeof(State)))) {
+ // Early processes (eg: init) do not have /dev/urandom yet, but we still
+ // have to provide them with some degree of entropy. Not having a secure
+ // seed is not as problematic for them, as they are less likely to be
+ // the target of heap based vulnerabilities exploitation attempts.
+ State[0] = NanoTime();
+ State[1] = 0;
+ }
+ fillCache();
}
+ u8 getU8() {
+ if (UNLIKELY(isCacheEmpty()))
+ fillCache();
+ const u8 Result = static_cast<u8>(CachedBytes & 0xff);
+ CachedBytes >>= 8;
+ CachedBytesAvailable--;
+ return Result;
+ }
+ u64 getU64() { return next(); }
+
private:
+ u8 CachedBytesAvailable;
+ u64 CachedBytes;
u64 State[2];
+ u64 next() {
+ const u64 S0 = State[0];
+ u64 S1 = State[1];
+ const u64 Result = S0 + S1;
+ S1 ^= S0;
+ State[0] = rotl(S0, 55) ^ S1 ^ (S1 << 14);
+ State[1] = rotl(S1, 36);
+ return Result;
+ }
+ bool isCacheEmpty() {
+ return CachedBytesAvailable == 0;
+ }
+ void fillCache() {
+ CachedBytes = next();
+ CachedBytesAvailable = sizeof(CachedBytes);
+ }
};
+typedef XoRoShiRo128Plus ScudoPrng;
+
} // namespace __scudo
#endif // SCUDO_UTILS_H_
generated by cgit v1.2.3 (git 2.25.1) at 2024-05-02 13:32:02 +0000