linux-kernel - Re: [PATCH 05/15] x86: Implement function

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Message-ID: <202104161555.B8C1E193@keescook>
Date:   Fri, 16 Apr 2021 15:58:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        X86 ML <x86@...nel.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 05/15] x86: Implement function_nocfi

On Fri, Apr 16, 2021 at 03:52:44PM -0700, Andy Lutomirski wrote:
> > > char entry_whatever[];
> > > wrmsrl(..., (unsigned long)entry_whatever);
> >
> > This is just casting. It'll still resolve to the jump table entry.
> 
> How?  As far as clang is concerned, entry_whatever isn't a function at
> all.  What jump table entry?

Whoops, sorry, I misread the [] as (). I thought you were just showing
an arbitrary function declaration, but I see what you mean now.

I am digesting the rest of your email now... :)

-- 
Kees Cook