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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 28 Feb 2022 14:35:11 -0800
Message-ID: <CAKwvOdkykPtGTL6ud8qJZHSHKV2eSbpnZE-G4oyymD9BiQKHdg@mail.gmail.com>
Subject: Re: [PATCH] [PATCH v2] AARCH64: Add gcc Shadow Call Stack support
To:     Dan Li <ashimida@linux.alibaba.com>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Marco Elver <elver@google.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        llvm@lists.linux.dev, linux-hardening@vger.kernel.org
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On Sun, Feb 27, 2022 at 11:37 PM Dan Li <ashimida@linux.alibaba.com> wrote:
>
>
>
> On 2/25/22 12:47, Miguel Ojeda wrote:
> > On Fri, Feb 25, 2022 at 4:24 AM Dan Li <ashimida@linux.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