linux-kernel - Re: [PATCH stable 5.4,5.10] x86/fpu: Correct pkru/xstate inconsistency

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Message-ID: <CADyq12yuzOPbv+jrdhf8unzsifVXGw31LbW+Sh2tZ3qG=xjGjg@mail.gmail.com>
Date:   Tue, 15 Feb 2022 21:01:54 -0500
From:   Brian Geffon <bgeffon@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Willis Kung <williskung@...gle.com>,
        Guenter Roeck <groeck@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        "# v4 . 10+" <stable@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH stable 5.4,5.10] x86/fpu: Correct pkru/xstate inconsistency

On Tue, Feb 15, 2022 at 4:42 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 2/15/22 13:32, Brian Geffon wrote:
> >> How was this tested, and what do the maintainers of this subsystem
> >> think?  And will you be around to fix the bugs in this when they are
> >> found?
> > This has been trivial to reproduce, I've used a small repro which I've
> > put here: https://gist.github.com/bgaff/9f8cbfc8dd22e60f9492e4f0aff8f04f
> > , I also was able to reproduce this using the protection_keys self
> > tests on a 11th Gen Core i5-1135G7.
>
> I've got an i7-1165G7, but I'm not seeing any failures on a
> 5.11 distro kernel.
>

Hi Dave,
I suspect the reason you're not seeing it is toolchain related, I'm
building with clang 14.0.0 and it produces the sequence of
instructions which use the cached value. Let me know if there is
anything I can do to help you investigate this further.

Brian