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Date:   Tue, 1 Nov 2022 14:39:57 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Joao Moreira <joao@overdrivepizza.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Sami Tolvanen <samitolvanen@google.com>,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT
Message-ID: <202211011437.F82B61B8C@keescook>
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On Mon, Oct 31, 2022 at 12:13:50PM -0700, Joao Moreira wrote:
> On 2022-10-18 22:19, Kees Cook wrote:
> > On Tue, Oct 18, 2022 at 09:48:42PM -0700, Joao Moreira wrote:
> > > > > Is it useful to get the compiler to emit 0xcc with
> > > > > -fpatchable-function-entry under any circumstance? I can probably
> > > > > change
> > > > > that quickly if needed/useful.
> > > >
> > > > Having it emit 0xcc for the bytes in front of the symbol might be
> > > > interesting. It would mean a few kernel changes, but nothing too hard.
> 
> Should I push for this within clang? I have the patch semi-ready (below) and
> would have some cycles this week for polishing it.

Sure! While the NOP vs CC issue isn't very interesting when IBT is
available, it's nice for non-IBT to make attackers have to target
addresses precisely.

If it's really invasive or hard to maintain in Clang (or objtool),
then I'd say leave it as-is.

-- 
Kees Cook