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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        kernel test robot <oliver.sang@intel.com>,
        Eric Biggers <ebiggers@google.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        kernel test robot <lkp@intel.com>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [x86/uaccess] 9c5743dff4:
 WARNING:at_arch/x86/mm/extable.c:#ex_handler_fprestore
In-Reply-To: <8735hbryn6.ffs@tglx>
References: <20220513085455.GB21013@xsang-OptiPlex-9020>
 <CAHk-=wjDE7tWc5k81P41AKw9b13ehrTX8XawgnP-wa6fA57kuA@mail.gmail.com>
 <8735hbryn6.ffs@tglx>
Date:   Sun, 15 May 2022 16:54:47 +0200
Message-ID: <87pmkerglk.ffs@tglx>
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On Sun, May 15 2022 at 10:25, Thomas Gleixner wrote:
> On Fri, May 13 2022 at 09:52, Linus Torvalds wrote:
> The code which copies the ptrace supplied state has a pile of sanity
> checks to catch invalid state, but I wouldn't bet my hat on it that it's
> 100% complete. We can be more defensive here, but I would be surprised.
>
> Something like the untested below. I'll expose it to some testing to see
> what explodes.

I was not able to get something broken past the existing sanity checks
which was caught by the trial restore. I seems the FPU units are pretty
resilent against random nonsense except for the XSTATE header and the
MXCRS content. Though I ponder to just add that trial restore due to
paranoia.

Thanks,

        tglx