linux-kernel - Re: [PATCH v4 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN

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Date:   Tue, 5 Oct 2021 22:56:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     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>,
        linux-hardening@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v4 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB

On Tue, Oct 05, 2021 at 01:29:02PM -0700, Sami Tolvanen wrote:
> On Mon, Oct 4, 2021 at 11:59 PM Peter Zijlstra <peterz@...radead.org> wrote:

> > For x86_64 it should indeed never get called, however if you plan on
> > supporting i386 then you need the annotation. Also, it might get called
> > on arm64 which is about to grow basic HAVE_STATIC_CALL support.
> 
> Good point. I read through the latest arm64 static call proposal and
> while it can fall back to an indirect call, it doesn't look like that
> would cause issues with CFI.

Because that call is outside of compiler control? Same will be true for
any HAVE_STATIC_CALL implementation I suppose. The trampoline will be
outside of compiler control.