Commit 9c573cd3 authored by Kees Cook's avatar Kees Cook
Browse files

randomize_kstack: Improve entropy diffusion 



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: default avatarArnd Bergmann <arnd@arndb.de>
Fixes: 39218ff4 ("stack: Optionally randomize kernel stack offset each syscall")
Link: https://lore.kernel.org/r/20240309202445.work.165-kees@kernel.org


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent bbda3ba6

include/linux/randomize_kstack.h

+1 −1
Original line number Diff line number Diff line
@@ -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)