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From:   Lai Jiangshan <jiangshanlai@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Joerg Roedel <jroedel@suse.de>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Juergen Gross <jgross@suse.com>, Chester Lin <clin@suse.com>
Subject: [PATCH V2 02/41] x86/traps: Remove stack-protector from traps.c
Date:   Sun, 26 Sep 2021 23:07:59 +0800
Message-Id: <20210926150838.197719-3-jiangshanlai@gmail.com>
In-Reply-To: <20210926150838.197719-1-jiangshanlai@gmail.com>
References: <20210926150838.197719-1-jiangshanlai@gmail.com>
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From: Lai Jiangshan <laijs@linux.alibaba.com>

When stack-protector is enabled, the compiler adds some instrument code
at the beginning and the end of some functions. Many functions in traps.c
are non-instrumentable.  Moreover, stack-protector code in the beginning
of the affected function accesses the canary that might be watched by
hardware breakpoints which also violate the non-instrumentable
nature of some functions and might cause infinite recursive #DB because
the canary is accessed before resetting the dr7.

So it is better to remove stack-protector from traps.c.

It is also prepared for later patches that move some entry code into
traps.c, some of which can NOT use percpu register until gsbase is
properly switched.  And stack-protector depends on the percpu register
to work.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/kernel/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 8f4e8fa6ed75..0e054e2304c6 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -48,6 +48,9 @@ KCOV_INSTRUMENT		:= n
 
 CFLAGS_head$(BITS).o	+= -fno-stack-protector
 
+CFLAGS_REMOVE_traps.o		= -fstack-protector -fstack-protector-strong
+CFLAGS_traps.o			+= -fno-stack-protector
+
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
 obj-y			:= process_$(BITS).o signal.o
-- 
2.19.1.6.gb485710b