linux-hardening - Re: [PATCH] static_call,x86: Robustify trampoline patching

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Message-ID: <YX8AQJqyB+H3PF1d@hirez.programming.kicks-ass.net>
Date:   Sun, 31 Oct 2021 21:44:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Mark Rutland <mark.rutland@....com>, X86 ML <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching

On Sun, Oct 31, 2021 at 09:21:56PM +0100, Ard Biesheuvel wrote:

> That means we can support static calls on arm64 now without breaking
> Clang CFI, and work on a solution for the redundant jumps on a more
> relaxed schedule.

Yes, arm64 has a 'problem' with having already merged the clang-cfi
stuff :/

I'm hoping the x86 solution can be an alternative CFI scheme, I'm
starting to really hate this one. And I'm not at all convinced the
proposed scheme is the best possible scheme given the constraints of
kernel code. AFAICT it's a compromise made in userspace.