[GWP-ASan] Fix PRNG to use IE TLS.
Summary:
GWP-ASan's PRNG didn't use Initial-Exec TLS. Fix that to ensure that we don't
have infinite recursion, and also that we don't allocate a DTV on Android when
GWP-ASan is touched.
Test coverage ensuring that the sample counter is UINT32_MAX for an
uninitialised GWP-ASan is provided by gwp_asan/tests/late_init.cpp.
Reviewers: pcc, cferris
Reviewed By: pcc
Subscribers: #sanitizers, llvm-commits, rprichard, eugenis
Tags: #sanitizers, #llvm
Differential Revision: https://reviews.llvm.org/D74135
GitOrigin-RevId: 25de3f98b8a7436404dbc185040645f2549a8a8f
diff --git a/guarded_pool_allocator.cpp b/guarded_pool_allocator.cpp
index 4ce4d80..7af99e4 100644
--- a/guarded_pool_allocator.cpp
+++ b/guarded_pool_allocator.cpp
@@ -99,6 +99,7 @@
else
AdjustedSampleRatePlusOne = 2;
+ initPRNG();
ThreadLocals.NextSampleCounter =
(getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1;
diff --git a/random.cpp b/random.cpp
index d8efe62..2180f92 100644
--- a/random.cpp
+++ b/random.cpp
@@ -11,9 +11,18 @@
#include <time.h>
+// Initialised to a magic constant so that an uninitialised GWP-ASan won't
+// regenerate its sample counter for as long as possible. The xorshift32()
+// algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
+// 0xfffffea4.
+GWP_ASAN_TLS_INITIAL_EXEC uint32_t RandomState = 0xff82eb50;
+
namespace gwp_asan {
+void initPRNG() {
+ RandomState = time(nullptr) + getThreadID();
+}
+
uint32_t getRandomUnsigned32() {
- thread_local uint32_t RandomState = time(nullptr) + getThreadID();
RandomState ^= RandomState << 13;
RandomState ^= RandomState >> 17;
RandomState ^= RandomState << 5;
diff --git a/random.h b/random.h
index 5fcf30d..953b989 100644
--- a/random.h
+++ b/random.h
@@ -12,6 +12,9 @@
#include <stdint.h>
namespace gwp_asan {
+// Initialise the PRNG, using time and thread ID as the seed.
+void initPRNG();
+
// xorshift (32-bit output), extremely fast PRNG that uses arithmetic operations
// only. Seeded using walltime.
uint32_t getRandomUnsigned32();
