From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Matt Fleming <matt.fleming@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state in irq ctxt
Date: Thu, 5 Jun 2014 18:08:42 +0200 [thread overview]
Message-ID: <20140605160842.GE16642@pd.tnic> (raw)
In-Reply-To: <CALCETrVqqgExhuAYawh_7tc8-Nm8GGiMxmtw25mLFoxru-odZg@mail.gmail.com>
On Thu, Jun 05, 2014 at 09:01:02AM -0700, Andy Lutomirski wrote:
> NMI might be okay. I haven't checked.
Well, if efi decides to do FPU math and it happens in NMI, we will have
to provide for proper contexts handling.
> It has to change back, though. Completely unrealistic and useless example:
>
> int ctxt = what_context_im_in();
>
> set_up_the_fpu(ctxt);
>
> // kprobe fires and changes the context
> // kprobe does something
And since we're being completely unrealistic, kprobe decides to use the
fpu too and uses it...
> // kprobe changes the context back
>
> use the FPU. Life is good.
>
> put_back_the_fpu(ctxt);
So you probably need some way of mapping preallocated, per-cpu FPU
contexts to their users which can get and put them.
It's a whole different question whether that makes sense though, at all
or we simply remain conservative and don't do any efi in NMI context...
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
next prev parent reply other threads:[~2014-06-05 16:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <tip-baa916f39b50ad91661534652110df40396acda0@git.kernel.org>
2014-06-04 22:17 ` [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state in irq ctxt H. Peter Anvin
2014-06-04 22:49 ` Borislav Petkov
2014-06-04 22:52 ` H. Peter Anvin
2014-06-05 0:19 ` Andy Lutomirski
2014-06-05 7:18 ` Borislav Petkov
2014-06-05 8:49 ` Matt Fleming
2014-06-05 9:02 ` Borislav Petkov
2014-06-05 15:44 ` Andy Lutomirski
2014-06-05 15:53 ` Borislav Petkov
2014-06-05 16:01 ` Andy Lutomirski
2014-06-05 16:08 ` Borislav Petkov [this message]
2014-06-05 16:14 ` Andy Lutomirski
2014-06-05 16:18 ` Borislav Petkov
2014-06-05 16:31 ` H. Peter Anvin
2014-06-05 16:35 ` Andy Lutomirski
2014-06-05 16:43 ` H. Peter Anvin
2014-06-05 16:37 ` Borislav Petkov
2014-06-05 16:43 ` H. Peter Anvin
2014-06-05 16:44 ` Borislav Petkov
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