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Subject: Re: [PATCH V2 02/41] x86/traps: Remove stack-protector from traps.c
To:     Borislav Petkov <bp@alien8.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Cc:     linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, 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>
References: <20210926150838.197719-1-jiangshanlai@gmail.com>
 <20210926150838.197719-3-jiangshanlai@gmail.com> <YVGalJLOyK235XvG@zn.tnic>
From:   Lai Jiangshan <laijs@linux.alibaba.com>
Message-ID: <d4e653e7-1f23-eec9-4db7-964298fc1dc5@linux.alibaba.com>
Date:   Mon, 27 Sep 2021 18:49:16 +0800
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On 2021/9/27 18:19, Borislav Petkov wrote:
> On Sun, Sep 26, 2021 at 11:07:59PM +0800, Lai Jiangshan wrote:
>> 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
> 
> Why this too?
> 
>> +CFLAGS_traps.o			+= -fno-stack-protector
> 
> Isn't this enough to disable stack protector for this file?
> 

I did not investigate deep enough.  I reviewed the generated code and
found %gs is accessed early for the C entry function and searched for
solution and I chose to copy the code that I thought is the most complete:
kernel/entry/Makefile

Using only "-fno-stack-protector" is enough to disable stack protector with
my .config, I'm not so sure about other configuration.

Thanks
Lai