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

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Date:	Fri, 13 May 2016 10:32:26 -0700
From:	Megha Dey <megha.dey@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: SHA1-MB algorithm broken on latest kernel

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

> 
> Thanks,
> 
> 	Ingo