6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook keescook@chromium.org
[ 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@arndb.de Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall") Link: https://lore.kernel.org/r/20240309202445.work.165-kees@kernel.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 5d868505a94e4..6d92b68efbf6c 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -80,7 +80,7 @@ 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)