kernel-hardening - Re: [PATCH v2 09/17] arm64: disable function graph tracing with SCS

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Message-ID: <CABCJKud1xYEx_GVgfBHUuwNGKMxX+uVaE5TR6DEqo7CoSJJnNA@mail.gmail.com>
Date: Tue, 29 Oct 2019 10:45:22 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Mark Rutland <mark.rutland@....com>, Nick Desaulniers <ndesaulniers@...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>, 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 v2 09/17] arm64: disable function graph tracing with SCS

On Fri, Oct 25, 2019 at 4:03 AM Mark Rutland <mark.rutland@....com> wrote:
> I'm guessing it's difficult to always figure out the SCS slot for an
> instrumented callsite unless we pass this explicitly from the ftrace
> entry code, so we'd probably have to change some common infrastructure
> for that.
>
> We have a similar issue with pointer authentication, and we're solving
> that with -fpatchable-function-entry, which allows us to hook the
> callsite before it does anything with the return address. IIUC we could
> use the same mechanism here (and avoid introducing a third).
>
> Are there plans to implement -fpatchable-function-entry on the clang
> side?

I'm not sure if there are plans at the moment, but if this feature is
needed for PAC, adding it to clang shouldn't be a problem. Nick, did
you have any thoughts on this?

Sami

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