5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
[ Upstream commit 9c573cd313433f6c1f7236fe64b9b743500c1628 ]
The kstack_offset variable was really only ever using the low bits for
kernel stack offset entropy. Add a ror32() to increase bit diffusion.
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall")
Link: https://lore.kernel.org/r/20240309202445.work.165-kees@xxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/randomize_kstack.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h
index d373f1bcbf7ca..5d52d15faee0c 100644
--- a/include/linux/randomize_kstack.h
+++ b/include/linux/randomize_kstack.h
@@ -58,7 +58,7 @@ DECLARE_PER_CPU(u32, kstack_offset);
if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
&randomize_kstack_offset)) { \
u32 offset = raw_cpu_read(kstack_offset); \
- offset ^= (rand); \
+ offset = ror32(offset, 5) ^ (rand); \
raw_cpu_write(kstack_offset, offset); \
} \
} while (0)
--
2.43.0
