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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Mon, 4 Nov 2019 15:42:09 -0800
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Subject: Re: [PATCH v4 10/17] arm64: disable kretprobes with SCS
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Dave Martin <Dave.Martin@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Laura Abbott <labbott@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
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On Mon, Nov 4, 2019 at 9:05 AM Mark Rutland <mark.rutland@arm.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.

Sami