linux-kernel - Re: [RFC] x86_64: A real proposal for iret-less return to kernel

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Message-ID: <20140521163315.GJ21205@pd.tnic>
Date:	Wed, 21 May 2014 18:33:15 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On Wed, May 21, 2014 at 08:21:57AM -0700, Andy Lutomirski wrote:
> ISTM the do_machine_check code ought to consider any kill-worthy MCE
> from kernel space to be non-recoverable, but I want to keep the scope
> of these patches under control.

MCA has a bit called RIPV which, if set, signals that RIP is valid and
it is safe to return provided we've taken proper care of handling even
non-correctable errors (memory poisoning, etc).

If RIPV is not set, we panic anyway.

> That being said, if an MCE that came from CPL0 never tried to return,
> this would be simpler.  I don't know enough about the machine check
> architecture to know whether that's a reasonable thing to do.

Yeah, there are cases where MCE can return, see above.

-- 
Regards/Gruss,
    Boris.

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