linux-kernel - Re: [RFC PATCH 00/21] KCFI support

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Message-ID: <202204291545.47C6A97EA2@keescook>
Date:   Fri, 29 Apr 2022 15:53:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev
Subject: Re: [RFC PATCH 00/21] KCFI support

On Fri, Apr 29, 2022 at 01:36:23PM -0700, Sami Tolvanen wrote:
> KCFI is a proposed forward-edge control-flow integrity scheme for
> Clang, which is more suitable for kernel use than the existing CFI
> scheme used by CONFIG_CFI_CLANG. KCFI doesn't require LTO, doesn't
> alter function references to point to a jump table, and won't break
> function address equality.

🎉 :)

> The latest LLVM patches are here:
> 
>   https://reviews.llvm.org/D119296
>   https://reviews.llvm.org/D124211
> 
> [...]
> To test this series, you'll need to compile your own Clang toolchain
> with the patches linked above. You can also find the complete source
> tree here:
> 
>   https://github.com/samitolvanen/llvm-project/commits/kcfi-rfc

And note that this RFC is seeking to break a bit of a circular dependency
with regard to the design of __builtin_kcfi_call_unchecked (D124211
above), as the implementation has gone around a few times in review within
LLVM, and we want to make sure that kernel folks are okay with what was
settled on. If there are no objections on the kernel side, then we can
land the KCFI patches, as this is basically the only remaining blocker.

-Kees

-- 
Kees Cook