linux-kernel - Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state in irq ctxt

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Message-ID: <20140605155307.GD16642@pd.tnic>
Date:	Thu, 5 Jun 2014 17:53:08 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state
 in irq ctxt

On Thu, Jun 05, 2014 at 08:44:20AM -0700, Andy Lutomirski wrote:
> Are there weird contexts from which EFI calls can happen? It looks
> like the current code isn't necessarily safe in things that aren't
> normal process context but aren't interrupts either (e.g. debug traps,
> #GP, etc).

The efi-pstore thing registers as a kmsg dumper which can be run in NMI
context and efi can be called there.

> I wonder if it would make sense at some point to maintain an explicit
> stack of kernel entries. There doesn't seem to be a reliable way to
> answer the question of "what context am I in" from C code right now.

So that you can ask int ctxt = what_context_Im_in() and then that
context can go and change right underneath you. :-)

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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