linux-kernel - Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction patching

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Message-ID: <20130710214848.GB14879@pd.tnic>
Date:	Wed, 10 Jul 2013 23:48:48 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>,
	Borislav Petkov <bpetkov@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction
 patching

On Wed, Jul 10, 2013 at 02:36:41PM -0700, H. Peter Anvin wrote:
> I'm wondering if it would be easier/more general to just return to the
> instruction. The "more general" bit would allow this to be used for
> other things, like alternatives, and perhaps eventually dynamic call
> patching.

Well, the aspect of not using stop_machine in alternatives is a don't
care because there we do text_poke_early on the BSP anyway. However,
there we toggle interrupts so it would probably be interesting to see
whether a non-interrupt-disabling variant would be faster.

> Returning to the instruction will, in effect, be a busy-wait for
> the faulted CPU until the patch is complete; more or less what
> stop_machine would do, but only for a CPU which actually strays into
> the affected region.

Oh, something like we patch in a two-byte jump first:

1:
	jmp 1b

until we finish patching the rest? Ha, interesting :).

-- 
Regards/Gruss,
    Boris.

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