Date: Tue, 5 Nov 2019 14:05:39 -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 Tue, Nov 5, 2019 at 11:55 AM Mark Rutland <mark.rutland@....com> wrote: > On Mon, Nov 04, 2019 at 03:44:39PM -0800, Sami Tolvanen wrote: > > 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. > > Ok, that makes sense to me. I'd suggest something like: > > | The graph tracer hooks returns by modifying frame records on the > | (regular) stack, but with SCS the return address is taken from the > | shadow stack, and the value in the frame record has no effect. As we > | don't currently have a mechanism to determine the corresponding slot > | on the shadow stack (and to pass this through the ftrace > | infrastructure), for now let's disable the graph tracer when SCS is > | enabled. > > ... as I suspect with some rework of the trampoline and common ftrace > code we'd be able to correctly manipulate the shadow stack for this. > Similarly, if clang gained -fpatchable-funciton-etnry, we'd get that for > free. That sounds good to me. Thanks, Mark. Sami
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