Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 6 Jul 2018 09:06:43 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Borislav Petkov <bp@alien8.de>, linux-crypto@vger.kernel.org,
        Mike Galbraith <efault@gmx.de>, torvalds@linux-foundation.org,
        tglx@linutronix.de, luto@kernel.org, peterz@infradead.org,
        brgerst@gmail.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
        dvlasenk@redhat.com, h.peter.anvin@intel.com,
        linux-tip-commits <linux-tip-commits@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] x86/crypto: Add missing RETs
Message-ID: <20180706140643.u2vau63nncg23hmi@treble>
References: <20180617194747.GA21160@zn.tnic>
 <1529289279.31745.3.camel@gmx.de>
 <20180623103622.GA2760@zn.tnic>
 <20180624071105.GA29407@gmail.com>
 <20180624104449.GA20159@avx2>
 <20180625072438.GA19063@gmail.com>
 <20180625131932.sge43esxdb5ejoxg@treble>
 <20180626064930.GB25879@gmail.com>
 <20180626123154.unjji5glpokedwal@treble>
 <20180705075815.GA20903@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20180705075815.GA20903@gmail.com>
User-Agent: NeoMutt/20180323
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jul 05, 2018 at 09:58:15AM +0200, Ingo Molnar wrote:
> 
> * Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 
> > > So that's still incomplete in that doesn't analyze the 32-bit build yet, right?
> > 
> > We could do INT3s on 64-bit and NOPs on 32-bit.
> > 
> > Or, possibly even better, we could just keep NOPs everywhere and instead
> > make objtool smart enough to detect function fallthroughs.  That should
> > be pretty easy, actually.  It already does it for C files.
> > 
> > Something like the below should work, though it's still got a few
> > issues:
> > 
> >   a) objtool is currently disabled for crypto code because it doesn't
> >      yet understand crypto stack re-alignments (which really needs
> >      fixing anyway); and
> > 
> >   b) it complains about the blank xen hypercalls falling through.  Those
> >      aren't actual functions anyway, so we should probably annotate
> >      those somehow so that objtool ignores them anyway.
> > 
> > I'm a bit swamped at the moment but I can fix those once I get a little
> > more bandwidth.  I at least verified that this patch caught the crypto
> > missing RETs.
> 
> Great, I'd be perfectly fine with such an approach.
> 
> Also, if we have that then we could re-apply Alexey's patch and switch to INT3 
> (only on 64-bit kernels) without any trouble, because objtool should detect any 
> execution flow bugs before the INT3 could trigger, right?
> 
> I.e. any INT3 fault would show a combination of *both* an objtool bug and a 
> probable code flow bug - which I suspect would warrant crashing the box ...

Sounds good to me.  I can take Alexey's patch and submit a 64-bit
version of it, along with the relevant objtool changes (though it may
still be a few weeks before I get the chance).

-- 
Josh