linux-kernel - Re: [PATCH v4 11/17] arm64: disable function graph tracing with SCS

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Message-ID: <CABCJKufDnLjP9vA-wSW0gSY05Cbr=NOpJ-WCh-bdj2ZNq7VNXw@mail.gmail.com>
Date:   Mon, 4 Nov 2019 15:44:39 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 11/17] arm64: disable function graph tracing with SCS

On Mon, Nov 4, 2019 at 9:11 AM Mark Rutland <mark.rutland@....com> wrote:
> Can you please elaborate on _how_ this is incompatible in the commit
> message?
>
> For example, it's not clear to me if you mean that's functionally
> incompatible, or if you're trying to remove return-altering gadgets.
>
> If there's a functional incompatibility, please spell that out a bit
> more clearly. Likewise if this is about minimizing the set of places
> that can mess with control-flow outside of usual function conventions.

Sure, I'll add a better description in v5. In this case, the return
address is modified in the kernel stack, which means the changes are
ignored with SCS.

Sami