[PATCH] D74135: [GWP-ASan] Fix PRNG to use IE TLS.

[Mitch Phillips via Phabricator via llvm-commits]

hctim updated this revision to Diff 242930.
hctim added a comment.

- Updated magic constant.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74135/new/

https://reviews.llvm.org/D74135

Files:
  compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
  compiler-rt/lib/gwp_asan/random.cpp
  compiler-rt/lib/gwp_asan/random.h


Index: compiler-rt/lib/gwp_asan/random.h
===================================================================
--- compiler-rt/lib/gwp_asan/random.h
+++ compiler-rt/lib/gwp_asan/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();
Index: compiler-rt/lib/gwp_asan/random.cpp
===================================================================
--- compiler-rt/lib/gwp_asan/random.cpp
+++ compiler-rt/lib/gwp_asan/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;
Index: compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
===================================================================
--- compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
+++ compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
@@ -99,6 +99,7 @@
   else
     AdjustedSampleRatePlusOne = 2;
 
+  initPRNG();
   ThreadLocals.NextSampleCounter =
       (getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1;
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D74135.242930.patch
Type: text/x-patch
Size: 1749 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200206/cc2fbae9/attachment.bin>