linux-kernel - Re: 2.6.37-rc7: Regression: b43: crashes in hwrng

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Message-ID: <20110106144254.GC8803@darkside.kls.lan>
Date:	Thu, 6 Jan 2011 15:42:55 +0100
From:	"Mario 'BitKoenig' Holbe" <Mario.Holbe@...Ilmenau.DE>
To:	Herbert Xu <herbert@...dor.hengli.com.au>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	Matt Mackall <mpm@...enic.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Harald Welte <HaraldWelte@...tech.com>,
	Michal Ludvig <michal@...ix.cz>
Subject: Re: 2.6.37-rc7: Regression: b43: crashes in hwrng_register()

On Fri, Jan 07, 2011 at 12:35:41AM +1100, Herbert Xu wrote:
> On Thu, Jan 06, 2011 at 02:15:16PM +0100, Mario 'BitKoenig' Holbe wrote:
> > 1. Having ECX on the clobber-list is not really necessary.
> > XSTORE doesn't touch ECX at all.
> > REP XSTORE would touch it, but for this ECX would be an input anyways.
> 
> The documentation wasn't clear whether ECX would be updated without
> the REP prefix so I included it to be on the safe side.  Unfortunately
> my only VIA machine is on another continent at the moment so I can't
> test it myself.  Can you verify that ECX isn't changed without the
> REP prefix?

session-log (including small test case) attached: ECX is not changed.

> > 2. Would you mind doing the same for EDX as you did for EDI?
> According to my documentation EDX isn't be modified (nor would it
> make sense as it would break REP XSTORE).  Are you seeing anything
> different?

http://linux.via.com.tw/support/beginDownload.action?eleid=181&fid=261
VIA PadLock Programming Guide, v1.66, 4th August 2005
2.1 XSTORE Instructions (page 9)
RNG Quality Factor: EDX
[...] Only the lower two bits of EDX are meaningful; the upper 30 bits
are ignored by the instruction and may be set to zero.
                                   ^^^^^^^^^^^^^^^^^^

http://hackipedia.org/Hardware/CPU/x86/chip,%20VIA/nano/Padlock,%20quick%20reference%20v0.95%20(July%2025th,%202008).pdf
PadLock Quick Reference, v0.95, 25th July 2008
RANDOM NUMBER GENERATION (page 3)
Register Usage: Output
EDX Bits 0:1 are unchanged, all higher order bits are zero.
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

See the attached session-log as well: those EDX bits are indeed zeroed.


Btw: I believe both documents are quite clear regarding ECX for XSTORE.


Mario
-- 
User sind wie ideale Gase - sie verteilen sich gleichmaessig ueber alle Platten

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