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Message-ID: <CAGG=3QUcQCQXff9Hk+eHrvbAhPT16BmFGNuAGcd-N0d-G8yBKg@mail.gmail.com> Date: Thu, 8 Sep 2022 22:16:04 +0100 From: Bill Wendling <morbo@...gle.com> To: Kees Cook <keescook@...omium.org> Cc: Peter Zijlstra <peterz@...radead.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Juergen Gross <jgross@...e.com>, "Srivatsa S. Bhat (VMware)" <srivatsa@...il.mit.edu>, Alexey Makhalov <amakhalov@...are.com>, VMware PV-Drivers Reviewers <pv-drivers@...are.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, virtualization@...ts.linux-foundation.org, LKML <linux-kernel@...r.kernel.org>, Nathan Chancellor <nathan@...nel.org>, clang-built-linux <llvm@...ts.linux.dev>, linux-hardening@...r.kernel.org Subject: Re: [PATCH 2/2] x86/paravirt: add extra clobbers with ZERO_CALL_USED_REGS enabled On Thu, Sep 8, 2022 at 12:10 AM Kees Cook <keescook@...omium.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@...gle.com> wrote: > > > > > > > > On Sat, Sep 3, 2022 at 12:18 AM Kees Cook <keescook@...omium.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
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