linux-kernel - [PATCH 2/9] x86/boot: Disable stack protector for early boot code

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Message-ID: <20231023211730.40566-3-brgerst@gmail.com>
Date:   Mon, 23 Oct 2023 17:17:23 -0400
From:   Brian Gerst <brgerst@...il.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Uros Bizjak <ubizjak@...il.com>,
        Brian Gerst <brgerst@...il.com>
Subject: [PATCH 2/9] 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 userspace is active and does not
need stack protector enabled.

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

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0000325ab98f..aff619054e17 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -39,6 +39,8 @@ KMSAN_SANITIZE_nmi.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
-- 
2.41.0