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Date:   Sat, 30 Apr 2022 12:07:50 -0400
From:   Kenton Groombridge <me@concord.sh>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
Subject: Re: [RFC PATCH 00/21] KCFI support
Message-ID: <20220430160750.ov7ddsq2vzibwrju@bubbles>
Mail-Followup-To: Sami Tolvanen <samitolvanen@google.com>,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
References: <20220429203644.2868448-1-samitolvanen@google.com>
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On 22/04/29 01:36PM, 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:
>=20
>   https://reviews.llvm.org/D119296
>   https://reviews.llvm.org/D124211

Many thanks for continuing to work on this! As a user who has been
following the evolution of this patch series for a while now, I have a
couple of burning questions:

1) The LLVM patch says that kCFI is not compatible with execute-only
memory. Is there a plan ahead for kCFI if and when execute-only memory
is implemented?

2) kCFI only checks indirect calls while Clang's traditional CFI has
more schemes like bad cast checking and so on. Are there any major
security tradeoffs as a result of this?

V/R

Kenton Groombridge

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