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

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Date:   Mon, 2 May 2022 08:31:35 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....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-hardening@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        llvm@...ts.linux.dev
Subject: Re: [RFC PATCH 00/21] KCFI support

On Sat, Apr 30, 2022 at 9:08 AM Kenton Groombridge <me@...cord.sh> wrote:
> 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?

There's no plan for executable-only memory right now, that would
require type hashes to be moved somewhere else to read-only memory.

> 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?

No, cfi-icall is only scheme that's relevant for the kernel. The other
schemes implemented in Clang are mostly useful for C++.

Sami