linux-kernel - Re: SHA1-MB algorithm broken on latest kernel

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Date:	Mon, 16 May 2016 09:44:09 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Megha Dey <megha.dey@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: SHA1-MB algorithm broken on latest kernel

On Fri, May 13, 2016 at 10:32:26AM -0700, Megha Dey wrote:
> On Fri, 2016-05-13 at 07:51 +0200, Ingo Molnar wrote:
> > * Herbert Xu <herbert@...dor.apana.org.au> wrote:
> > 
> > > On Thu, May 12, 2016 at 04:31:06PM -0700, Megha Dey wrote:
> > > > Hi,
> > > >  
> > > > When booting latest kernel with the CONFIG_CRYPTO_SHA1_MB enabled, I
> > > > observe a panic.
> > > >  
> > > > After having a quick look, on reverting the following patches, I am able
> > > > to complete the booting process.
> > > > aec4d0e301f17bb143341c82cc44685b8af0b945
> > > > 8691ccd764f9ecc69a6812dfe76214c86ac9ba06
> > > > 68874ac3304ade7ed5ebb12af00d6b9bbbca0a16
> > > >  
> > > > Of the 3 patches, aec4d0e301f17bb143341c82cc44685b8af0b945 seems wrong.
> > > > The r10 to r15 registers are used in sha1_x8_avx2.S, which is called
> > > > from sha1_mb_mgr_flush_avx2.S.
> > > >
> > > > I do not think the functionality of the SHA1-MB crypto algorithm has
> > > > been tested after applying these changes. (I am not sure if any of the
> > > > other crypto algorithms have been affected by these changes).
> > > 
> > > Josh, Ingo:
> > > 
> > > Any ideas on this? Should we revert?
> > 
> > Yeah, I think so - although another option would be to standardize sha1_x8_avx2() 
> > - the problem is that it is a function that clobbers registers without 
> > saving/restoring them, breaking the C function ABI. I realize it's written in 
> > assembly, but unless there are strong performance reasons to deviate from the 
> > regular calling convention it might make sense to fix that.
> > 
> > Do any warnings get generated after the revert, if you enable 
> > CONFIG_STACK_VALIDATION=y?
> 
> After the revert and enabling CONFIG_STACK_VALIDATION:
> arch/x86/crypto/sha1-mb/sha1_mb_mgr_flush_avx2.o: warning: objtool:
> sha1_mb_mgr_flush_avx2()+0x20d: call without frame pointer save/setup
> 
> arch/x86/crypto/sha1-mb/sha1_mb_mgr_submit_avx2.o: warning: objtool:
> sha1_mb_mgr_submit_avx2()+0x115: call without frame pointer save/setup

Megha,

Sorry for breaking it.  I completely missed the fact that the function
calls sha1_x8_avx2() which clobbers registers.

If the performance penalty isn't too bad, I'll submit a patch to
standardize sha1_x8_avx2() to follow the C ABI.

Do you have any tips for testing this code?  I've tried using the tcrypt
module, but no luck.

-- 
Josh