linux-hardening - Re: [PATCH] [PATCH] AARCH64: Add gcc Shadow Call Stack support

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Date:   Wed, 23 Feb 2022 00:50:21 -0800
From:   Dan Li <ashimida@...ux.alibaba.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     catalin.marinas@....com, will@...nel.org, ndesaulniers@...gle.com,
        keescook@...omium.org, masahiroy@...nel.org, tglx@...utronix.de,
        akpm@...ux-foundation.org, mark.rutland@....com,
        samitolvanen@...gle.com, npiggin@...il.com, linux@...ck-us.net,
        mhiramat@...nel.org, ojeda@...nel.org, luc.vanoostenryck@...il.com,
        elver@...gle.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] [PATCH] AARCH64: Add gcc Shadow Call Stack support



On 2/22/22 08:16, Nathan Chancellor wrote:
> On Tue, Feb 22, 2022 at 01:57:36AM -0800, Dan Li wrote:
>> Shadow call stack is available in GCC > 11.2.0, this patch makes
>> the corresponding kernel configuration available when compiling
>> the kernel with gcc.
>>   config SHADOW_CALL_STACK
>> -	bool "Clang Shadow Call Stack"
>> -	depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
>> +	bool "Shadow Call Stack"
>> +	depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
>>   	depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
>>   	help
>> -	  This option enables Clang's Shadow Call Stack, which uses a
>> +	  This option enables Clang/GCC's Shadow Call Stack, which uses a
> 
> I wonder if we want to just ditch the mention of the compiler if both
> support it?
> 

My intention is to remind users that this is a compiler feature.
But since there is also a hint in CC_HAVE_SHADOW_CALL_STACK:
+# Supported by clang >= 7.0 or GCC ...

Removing the specific compiler here also looks fine to me.
Would this look better?

"This option enables Shadow Call Stack, which uses a ..."

or maybe:

"This option enables compiler's Shadow Call Stack, which uses a ..."

>>   	  shadow stack to protect function return addresses from being
>>   	  overwritten by an attacker. More information can be found in
>>   	  Clang's documentation:
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 09b885cc4db5..a48a604301aa 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -1255,7 +1255,7 @@ config HW_PERF_EVENTS
>>   config ARCH_HAS_FILTER_PGPROT
>>   	def_bool y
>>   
>> -# Supported by clang >= 7.0
>> +# Supported by clang >= 7.0 or GCC > 11.2.0
> 
> Same thing here, although eventually there may be a minimum GCC version
> bump to something newer than 11.2.0, which would allow us to just drop
> CONFIG_CC_HAVE_SHADOW_CALL_STACK altogether. No strong opinion.
> 

As Guenter said, I thought maybe we could mark the minimum available
version for users :)

Thanks,
Dan.