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From: Andy Lutomirski <luto@amacapital.net>
To: Borislav Petkov <bp@alien8.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	X86 ML <x86@kernel.org>
Subject: Re: WARNING: CPU: 0 PID: 3031 at ./arch/x86/include/asm/fpu/internal.h:530 fpu__restore+0x90/0x130()
Date: Mon, 15 Feb 2016 18:25:10 -0800	[thread overview]
Message-ID: <CALCETrW3r89hbU3u2xG2u+ZDrk-WzwmicL9ZL-L1GVGZfH-sdQ@mail.gmail.com> (raw)
In-Reply-To: <20160215191422.GB32716@pd.tnic>

On Feb 15, 2016 12:14 PM, "Borislav Petkov" <bp@alien8.de> wrote:
>
> ---
> From: Borislav Petkov <bp@suse.de>
> Date: Mon, 15 Feb 2016 19:50:33 +0100
> Subject: [RFC PATCH] x86/FPU: Fix double FPU regs activation
>
> On the entry_INT80_32->do_syscall_32_irqs_on path on 32-bit we run with
> interrupts enabled.

I would change this a little bit.

sys_sigreturn calls fpu__restore_sig with interrupts enabled.  When
restoring a 32-bit signal frame, it can happen that...

> And it can happen that we get preempted right after
> setting ->fpstate_active in a task's FPU.
>
> After we get preempted, we switch between tasks merrily and eventually
> are about to switch to that task above whose ->fpstate_active we
> set. We enter __switch_to() and do switch_fpu_prepare(). Our task gets
> ->fpregs_active set, we find ourselves back on the call stack below and
> especially in __fpu__restore_sig() which sets ->fpregs_active again.
>
> Leading to that whoops below.

--Andy

  reply	other threads:[~2016-02-16  2:25 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-11 19:27 WARNING: CPU: 0 PID: 3031 at ./arch/x86/include/asm/fpu/internal.h:530 fpu__restore+0x90/0x130() Borislav Petkov
2016-02-11 23:47 ` Andy Lutomirski
2016-02-12  1:16   ` Andy Lutomirski
2016-02-12 17:00     ` Borislav Petkov
2016-02-15 19:14       ` Borislav Petkov
2016-02-16  2:25         ` Andy Lutomirski [this message]
2016-02-17  8:16           ` Ingo Molnar
2016-02-17  9:29             ` Borislav Petkov
2016-02-17  9:35               ` Ingo Molnar
2016-02-17 10:31                 ` Borislav Petkov
2016-02-17 11:06                   ` Ingo Molnar
2016-02-17 11:41                   ` Borislav Petkov
2016-02-17 17:52               ` Andy Lutomirski
2016-02-15 19:05     ` Borislav Petkov
2016-02-12 11:17   ` Borislav Petkov

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