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SubjectRe: [PATCH] [PATCH] AARCH64: Add gcc Shadow Call Stack support
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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.

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