[PATCH v2 nolibc 27/53] tools/nolibc: ensure stack protector guard is never zero

Paul E. McKenney
2023-06-12T20:51:51Z

The all-zero pattern is one of the more probable out-of-bound writes so
add a special case to not accidentally accept it.

Also it enables the reliable detection of stack protector initialization
during testing.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
tools/include/nolibc/stackprotector.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/stackprotector.h b/tools/include/nolibc/stackprotector.h
index 77e5251c4490..b0156fc077a0 100644
--- a/tools/include/nolibc/stackprotector.h
+++ b/tools/include/nolibc/stackprotector.h
@@ -45,8 +45,9 @@ __attribute__((weak,no_stack_protector,section(".text.nolibc_stack_chk")))
void __stack_chk_init(void)
{
my_syscall3(__NR_getrandom, &__stack_chk_guard, sizeof(__stack_chk_guard), 0);
- /* a bit more randomness in case getrandom() fails */
- __stack_chk_guard ^= (uintptr_t) &__stack_chk_guard;
+ /* a bit more randomness in case getrandom() fails, ensure the guard is never 0 */
+ if (__stack_chk_guard != (uintptr_t) &__stack_chk_guard)
+ __stack_chk_guard ^= (uintptr_t) &__stack_chk_guard;
}
#endif /* defined(NOLIBC_STACKPROTECTOR) */

--
2.40.1