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

[Dan Li]

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.