linux-kernel - Re: [PATCH v13 01/12] add support for Clang's Shadow Call Stack (SCS)

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Message-ID: <CANiq72=vvRcjWCON7zbaCTxLA2wP_-5zrnLyymR4g9b1gwc5kg@mail.gmail.com>
Date:   Mon, 27 Apr 2020 18:48:49 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 01/12] add support for Clang's Shadow Call Stack (SCS)

On Mon, Apr 27, 2020 at 6:00 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index 333a6695a918..18fc4d29ef27 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -42,3 +42,9 @@
>   * compilers, like ICC.
>   */
>  #define barrier() __asm__ __volatile__("" : : : "memory")
> +
> +#if __has_feature(shadow_call_stack)
> +# define __noscs       __attribute__((__no_sanitize__("shadow-call-stack")))
> +#else
> +# define __noscs
> +#endif

Can we remove the `#else` branch? compiler_types.h [*] has to care
anyway about that case for other compilers anyway, no?

> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index e970f97a7fcb..97b62f47a80d 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -193,6 +193,10 @@ struct ftrace_likely_data {
>  # define randomized_struct_fields_end
>  #endif
>
> +#ifndef __noscs
> +# define __noscs
> +#endif

[*] Here

Cheers,
Miguel