linux-hardening - Re: [PATCH v5 00/15] x86: Add support for Clang CFI

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Date:   Thu, 28 Oct 2021 13:09:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        X86 ML <x86@...nel.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 v5 00/15] x86: Add support for Clang CFI

On Wed, Oct 27, 2021 at 03:27:59PM -0700, Kees Cook wrote:

> Right -- though wouldn't just adding __ro_after_init do the same?
> 
> DEFINE_STATIC_CALL(static_call_name, func_a) __ro_after_init;

That breaks modules (and your jump_label patch doing the same is
similarly broken).

When a module is loaded that uses the static_call(), it needs to
register it's .static_call_sites range with the static_call_key which
requires modifying it.