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;
MIME-Version: 1.0
References: <20220902213750.1124421-1-morbo@google.com> <20220902213750.1124421-3-morbo@google.com>
 <202209022251.B14BD50B29@keescook> <CAGG=3QXpK+bFOSYZkdNNFGzNfgJSSADGTRWYRv6z0vfBAgQvWQ@mail.gmail.com>
 <CAKwvOdm+kVTrqMrSPHwTa0NrG9qwTcFkGnikjYjk0ctFGBfeRA@mail.gmail.com>
 <YxhbO1YZPMHutw48@hirez.programming.kicks-ass.net> <202209071609.BE5BF18D6@keescook>
In-Reply-To: <202209071609.BE5BF18D6@keescook>
From:   Bill Wendling <morbo@google.com>
Date:   Thu, 8 Sep 2022 22:16:04 +0100
Message-ID: <CAGG=3QUcQCQXff9Hk+eHrvbAhPT16BmFGNuAGcd-N0d-G8yBKg@mail.gmail.com>
Subject: Re: [PATCH 2/2] x86/paravirt: add extra clobbers with
 ZERO_CALL_USED_REGS enabled
To:     Kees Cook <keescook@chromium.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Juergen Gross <jgross@suse.com>,
        "Srivatsa S. Bhat (VMware)" <srivatsa@csail.mit.edu>,
        Alexey Makhalov <amakhalov@vmware.com>,
        VMware PV-Drivers Reviewers <pv-drivers@vmware.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        virtualization@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        linux-hardening@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Sep 8, 2022 at 12:10 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Sep 07, 2022 at 10:50:03AM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 06, 2022 at 11:00:07PM -0700, Nick Desaulniers wrote:
> > > On Sun, Sep 4, 2022 at 11:02 PM Bill Wendling <morbo@google.com> wrote:
> > > >
> > > > On Sat, Sep 3, 2022 at 12:18 AM Kees Cook <keescook@chromium.org> wrote:
> > > > >
> > > > > On Fri, Sep 02, 2022 at 09:37:50PM +0000, Bill Wendling wrote:
> > > > > > [...]
> > > > > >         callq   *pv_ops+536(%rip)
> > > > >
> > > > > Do you know which pv_ops function is this? I can't figure out where
> > > > > pte_offset_kernel() gets converted into a pv_ops call....
> > > > >
> > > > This one is _paravirt_ident_64, I believe. I think that the original
> > > > issue Nathan was seeing was with another seemingly innocuous function.
> > >
> > > _paravirt_ident_64 is marked noinstr, which makes me suspect that it
> > > really needs to not be touched at all by the compiler for
> > > these...special features.
> >
> > My source tree sayeth:
> >
> >   u64 notrace _paravirt_ident_64(u64 x)
>
> I don't see noinstr either. But it seems a reasonable thing to do?
>
> Bill, does fixing up the noinstr macro and adding it here fix the
> problem?
>
[sorry for late response]

Let me give it a shot. I'll also test out Peter's suggestion, which
might be a better option in the long run. I suspect that we'll need to
devise similar patches for other places, but it shouldn't be hard to
find them all.

-bw

-bw