linux-kernel - Re: [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool whitelist

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Message-ID: <569F2027.1070502@zytor.com>
Date:	Tue, 19 Jan 2016 21:50:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool
 whitelist

On 01/19/16 21:42, Josh Poimboeuf wrote:
>>>>
>>>>   Apparently(?) xen treats the ud2 special when it's followed by "78 65
>>>>   6e".  This is confusing for stacktool because ud2 is normally a dead
>>>>   end, and it thinks the instructions after it will never run.
>>>>   

Cute.  UD2 followed by three ASCII characters.  I guess that becomes
really fun when using UD2 + a string for error reporting.  Of course, no
software does that...

	-hpa