linux-kernel - Re: [PATCH v4 10/17] arm64: disable kretprobes with SCS

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Message-ID: <20191105090426.GA4743@lakrids.cambridge.arm.com>
Date:   Tue, 5 Nov 2019 09:04:26 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Sami Tolvanen <samitolvanen@...gle.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 10/17] arm64: disable kretprobes with SCS

On Mon, Nov 04, 2019 at 03:42:09PM -0800, Sami Tolvanen wrote:
> On Mon, Nov 4, 2019 at 9:05 AM Mark Rutland <mark.rutland@....com> wrote:
> > I'm a bit confused as to why that's the case -- could you please
> > elaborate on how this is incompatible?
> >
> > IIUC kretrobes works by patching the function entry point with a BRK, so
> > that it can modify the LR _before_ it is saved to the stack. I don't see
> > how SCS affects that.
> 
> You're correct. While this may not be optimal for reducing attack
> surface, I just tested this to confirm that there's no functional
> conflict. I'll drop this and related patches from v5.

Great; thanks for confirming!

Mark.