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From:   Arvind Sankar <nivedita@alum.mit.edu>
To:     x86@kernel.org, Joerg Roedel <jroedel@suse.de>,
        Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH v2 5/5] x86/head/64: Disable stack protection for head$(BITS).o
Date:   Thu,  8 Oct 2020 15:16:23 -0400
Message-Id: <20201008191623.2881677-6-nivedita@alum.mit.edu>
In-Reply-To: <20201008191623.2881677-1-nivedita@alum.mit.edu>
References: <20201008191623.2881677-1-nivedita@alum.mit.edu>
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On 64-bit, the startup_64_setup_env() function added in
  866b556efa12 ("x86/head/64: Install startup GDT")
has stack protection enabled because of set_bringup_idt_handler().

At this point, %gs is not yet initialized, and this doesn't cause a
crash only because the #PF handler from the decompressor stub is still
installed and handles the page fault.

Disable stack protection for the whole file, and do it on 32-bit as
well to avoid surprises.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
 arch/x86/kernel/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 04ceea8f4a89..68608bd892c0 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -47,6 +47,8 @@ endif
 # non-deterministic coverage.
 KCOV_INSTRUMENT		:= n
 
+CFLAGS_head$(BITS).o	+= -fno-stack-protector
+
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
 obj-y			:= process_$(BITS).o signal.o
-- 
2.26.2