[tip: x86/asm] x86/boot: Disable stack protector for early boot code

[tip-bot2 for Brian Gerst]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     a9a76b38aaf577887103e3ebb41d70e6aa5a4b19
Gitweb:        https://git.kernel.org/tip/a9a76b38aaf577887103e3ebb41d70e6aa5a4b19
Author:        Brian Gerst <brgerst@xxxxxxxxx>
AuthorDate:    Thu, 23 Jan 2025 14:07:35 -05:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 18 Feb 2025 10:14:51 +01:00

x86/boot: Disable stack protector for early boot code

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 user-space is active and does not
need stack protector enabled.

Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250123190747.745588-4-brgerst@xxxxxxxxx
---
 arch/x86/kernel/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index b43eb7e..84cfa17 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -44,6 +44,8 @@ KCOV_INSTRUMENT_unwind_orc.o				:= n
 KCOV_INSTRUMENT_unwind_frame.o				:= n
 KCOV_INSTRUMENT_unwind_guess.o				:= n
 
+CFLAGS_head32.o := -fno-stack-protector
+CFLAGS_head64.o := -fno-stack-protector
 CFLAGS_irq.o := -I $(src)/../include/asm/trace
 
 obj-y			+= head_$(BITS).o