[PATCH v4 03/16] x86/boot: Disable stack protector for early boot code

Brian Gerst
2024-03-22T16:52:51Z

On 64-bit, this will prevent crashes when the canary access is changed
from %gs:40 to %gs:__stack_chk_guard(%rip). RIP-relative addresses from
the identity-mapped early boot code will target the wrong address with
zero-based percpu. KASLR could then shift that address to an unmapped
page causing a crash on boot.

This early boot code runs well before userspace is active and does not
need stack protector enabled.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
arch/x86/kernel/Makefile | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 5d128167e2e2..9884d2c9de15 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -40,6 +40,8 @@ KMSAN_SANITIZE_sev.o := n
KCOV_INSTRUMENT_head$(BITS).o := n
KCOV_INSTRUMENT_sev.o := n

+CFLAGS_head32.o := -fno-stack-protector
+CFLAGS_head64.o := -fno-stack-protector
CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace

obj-y += head_$(BITS).o
--
2.44.0