Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 18 Oct 2022 22:33:17 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Joao Moreira <joao@overdrivepizza.com>
Cc:     David Laight <David.Laight@aculab.com>,
        '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: <202210182232.FC83CB5@keescook>
References: <Y06rtoE9BsERG9uv@hirez.programming.kicks-ass.net>
 <9bb036e48580454b81e6de7224c5f006@AcuMS.aculab.com>
 <3edb387ea335085dcb6dd49f1d9c9ce6@overdrivepizza.com>
 <202210181013.923F8809@keescook>
 <24d4e2f277ecaa435075745817f2bd61@overdrivepizza.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <24d4e2f277ecaa435075745817f2bd61@overdrivepizza.com>
Precedence: bulk

On Tue, Oct 18, 2022 at 01:09:25PM -0700, Joao Moreira wrote:
> On 2022-10-18 10:20, Kees Cook wrote:
> > On Tue, Oct 18, 2022 at 08:58:24AM -0700, Joao Moreira wrote:
> > > > Does the hash value for kCFI only depend on the function type?
> > > > Or is there something like a attribute that can also be included?
> > > 
> > > Hi David -- does this sound like what you are asking about?
> > > 
> > > https://github.com/ClangBuiltLinux/linux/issues/1736
> > > 
> > > If yes, then it is something in our todo list :) I think Sami is
> > > handling
> > > it.
> > 
> > I was hoping someone with prior experience with Call Graph Detaching to
> > solve Transitive Clustering Relaxation[1] could assist? ;)
> 
> Hi Kees, thanks for bringing these slides up.
> 
> Yeah, I would be glad to help out with automating this sort of analysis.
> CGD, as explained in these slides would not help much here, because it was
> more of an optimization to reduce the number of allowed targets on returns
> (we did not have an almighty shadow stack at the time). Yet there are lots
> of other things we might be able to do, both statically and dynamically.
> Recent relevant research about this is multi-layer type analysis [1], which
> I may find the time to look into more deeply soon.
> 
> 1 - https://www-users.cse.umn.edu/~kjlu/papers/mlta.pdf

Awesome! Yeah, getting the big "common" hashes broken up by separate
clusters would be lovely.

-- 
Kees Cook