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Date:   Mon, 28 Feb 2022 14:35:11 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Dan Li <ashimida@...ux.alibaba.com>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Marco Elver <elver@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] [PATCH v2] AARCH64: Add gcc Shadow Call Stack support

On Sun, Feb 27, 2022 at 11:37 PM Dan Li <ashimida@...ux.alibaba.com> wrote:
>
>
>
> On 2/25/22 12:47, Miguel Ojeda wrote:
> > On Fri, Feb 25, 2022 at 4:24 AM Dan Li <ashimida@...ux.alibaba.com> wrote:
> >>
> >> +         - Clang (https://clang.llvm.org/docs/ShadowCallStack.html)
> >> +         - GCC (https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options)
> >
> > Maybe Clang: and GCC: instead of the parenthesis?
> >
> Got it.
>
> >> +#ifdef CONFIG_SHADOW_CALL_STACK
> >> +#define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
> >> +#endif
> >
> > Since both compilers have it, and I guess the `#ifdef` condition would
> > work for both, could this be moved into `compiler_types.h` where the
> > empty `__noscs` definition is, and remove the one from
> > `compiler-clang.h`?
> >
> In the clang documentation I see __has_feature(shadow_call_stack) is
> used to check if -fsanitize=shadow-call-stack is enabled, so I think
> maybe it's fine to use "#ifdef CONFIG_SHADOW_CALL_STACK"
> instead of "#if __has_attribute(__no_sanitize_address__)" here, then
> move it to `compiler_types.h`.

Or simply add a #define for __noscs to include/linux/compiler-gcc.h
with appropriate guard and leave the existing #ifndef in
include/linux/compiler_types.h as is.  I'd prefer that when the
compilers differ in terms of feature detection since it's as explicit
as possible.

>
> And from the results of my local clang 12 compilation, this doesn't
> seem to be a problem.
>
> Link: https://clang.llvm.org/docs/ShadowCallStack.html#has-feature-shadow-call-stack



-- 
Thanks,
~Nick Desaulniers

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