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stack protector: use AT_RANDOM

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Populate the stack canaries from the kernel supplied
AT_RANDOM value, which doesn't involve any system calls.
This is slightly faster (6 fewer syscalls) and avoids
unnecessarily reading /dev/urandom, which depletes entropy.

Bug: 7959813

Change-Id: If2b43100a2a9929666df3de56b6139fed969e0f1
This commit is contained in:
Nick Kralevich
2013-01-14 14:46:26 -08:00
parent 14e1975e13
commit e3a49a8661
6 changed files with 35 additions and 50 deletions
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16
tests/stack_protector_test.cpp
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@@ -56,13 +56,7 @@ struct stack_protector_checker {
// Duplicate tid. gettid(2) bug? Seeing this would be very upsetting.
ASSERT_TRUE(tids.find(tid) == tids.end());
#ifdef __GLIBC__
// glibc uses the same guard for every thread. bionic uses a different guard for each one.
#else
// Duplicate guard. Our bug. Note this is potentially flaky; we _could_ get the
// same guard for two threads, but it should be vanishingly unlikely.
ASSERT_TRUE(guards.find(guard) == guards.end());
#endif
// Uninitialized guard. Our bug. Note this is potentially flaky; we _could_ get
// four random zero bytes, but it should be vanishingly unlikely.
ASSERT_NE(guard, 0U);
@@ -78,7 +72,7 @@ static void* ThreadGuardHelper(void* arg) {
return NULL;
}
TEST(stack_protector, guard_per_thread) {
TEST(stack_protector, same_guard_per_thread) {
stack_protector_checker checker;
size_t thread_count = 10;
for (size_t i = 0; i < thread_count; ++i) {
@@ -90,12 +84,8 @@ TEST(stack_protector, guard_per_thread) {
}
ASSERT_EQ(thread_count, checker.tids.size());
// glibc uses the same guard for every thread. bionic uses a different guard for each one.
#ifdef __BIONIC__
ASSERT_EQ(thread_count, checker.guards.size());
#else
// bionic x86 and glibc uses the same guard for every thread.
ASSERT_EQ(1U, checker.guards.size());
#endif
}
#endif