linux-kernel - Re: [PATCH 1/2 v3] x86: introduce int3-based instruction patching

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Message-ID: <51DF2566.8000806@linux.intel.com>
Date:	Thu, 11 Jul 2013 14:36:38 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Jiri Kosina <jkosina@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...mai.com>, Joe Perches <joe@...ches.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 v3] x86: introduce int3-based instruction patching

On 07/11/2013 02:04 PM, Borislav Petkov wrote:
> On Thu, Jul 11, 2013 at 01:53:16PM -0700, H. Peter Anvin wrote:
>> Has anyone talked to AMD or VIA about this at all?
> 
> I guess I can try to take care of the AMD part. Just to confirm, is this
> the exact sequence we're interested in:
> 
> 1. Setup int3 handler for fixup.
> 
> 2. Put a breakpoint (int3) on the first byte of modifying region, and
> synchronize code on all CPUs.
> 
> 3. Modify other bytes of modifying region.
> 
> 4. Modify the first byte of modifying region, and synchronize code on
> all CPUs.
> 
> 5. Clear int3 handler.
> 
> If a suitable int3 handler is left permanently in place then the
> synchronization in step 4 is unnecessary.
> 

Correct.

	-hpa

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