| From ebcd951dcbe98a5c15790b13f1923c040f105278 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Sat, 9 Mar 2024 12:24:48 -0800 |
| Subject: randomize_kstack: Improve entropy diffusion |
| |
| 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) |
| -- |
| 2.43.0 |
| |
