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From: Ard Biesheuvel <ardb@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	 will@kernel.org, mark.rutland@arm.com, maz@kernel.org,
	 Sami Tolvanen <samitolvanen@google.com>,
	Fangrui Song <maskray@google.com>,
	 Nick Desaulniers <ndesaulniers@google.com>,
	Dan Li <ashimida@linux.alibaba.com>
Subject: Re: [PATCH v3 3/3] arm64: implement dynamic shadow call stack for Clang
Date: Mon, 13 Jun 2022 18:50:19 +0200	[thread overview]
Message-ID: <CAMj1kXGV8OdzS_LiYs50Q-Gx=MrJyW_WfK20R-FKf7FPX7kzyA@mail.gmail.com> (raw)
In-Reply-To: <202206130927.C1BF21FB83@keescook>

On Mon, 13 Jun 2022 at 18:30, Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Jun 13, 2022 at 03:40:08PM +0200, Ard Biesheuvel wrote:
> > Implement dynamic shadow call stack support on Clang, by parsing the
> > unwind tables at init time to locate all occurrences of PACIASP/AUTIASP
> > instructions, and replacing them with the shadow call stack push and pop
> > instructions, respectively.
> >
> > This is useful because the overhead of the shadow call stack is
> > difficult to justify on hardware that implements pointer authentication
> > (PAC), and given that the PAC instructions are executed as NOPs on
> > hardware that doesn't, we can just replace them without breaking
> > anything. As PACIASP/AUTIASP are guaranteed to be paired with respect to
> > manipulations of the return address, replacing them 1:1 with shadow call
> > stack pushes and pops is guaranteed to result in the desired behavior.
>
> Specifically, the "PAC available" benefit is the per-thread memory
> savings (no shadow stack needs to be allocated). Thanks for getting this
> working!
>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>
> Sami, can you test this for the cases you've needed this for?
>
> In the meantime, Will, can you land this for -next so we can get maximal
> test time?
>

I should note that this relies on Clang 15 which has not been released yet.

I have been using the clang-15 and lld-15 packages from

deb http://apt.llvm.org/bullseye/ llvm-toolchain-bullseye main

and setting LLVM=-15 on the make command line.

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  reply	other threads:[~2022-06-13 16:51 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-13 13:40 [PATCH v3 0/3] arm64: dynamic shadow call stack support Ard Biesheuvel
2022-06-13 13:40 ` [PATCH v3 1/3] arm64: unwind: add asynchronous unwind tables to kernel and modules Ard Biesheuvel
2022-06-15 16:50   ` Sami Tolvanen
2022-06-15 16:53     ` Ard Biesheuvel
2022-06-15 21:29       ` Kees Cook
2022-06-15 21:52         ` Fangrui Song
2022-06-16  7:14           ` Ard Biesheuvel
2022-06-16  7:24             ` Fangrui Song
2022-06-13 13:40 ` [PATCH v3 2/3] scs: add support for dynamic shadow call stacks Ard Biesheuvel
2022-06-14  6:20   ` Ard Biesheuvel
2022-06-15 17:12     ` Sami Tolvanen
2022-06-16  7:14       ` Ard Biesheuvel
2022-06-13 13:40 ` [PATCH v3 3/3] arm64: implement dynamic shadow call stack for Clang Ard Biesheuvel
2022-06-13 16:30   ` Kees Cook
2022-06-13 16:50     ` Ard Biesheuvel [this message]
2022-06-15 21:32   ` Sami Tolvanen
2022-06-16 10:51     ` Ard Biesheuvel

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