linux-kernel - Re: [bug] crypto/vmx/p8_ghash memory corruption in 4.8-rc7

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Date:   Wed, 28 Sep 2016 09:55:58 -0300
From:   Marcelo Cerri <marcelo.cerri@...onical.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Jan Stancek <jstancek@...hat.com>,
        rui y wang <rui.y.wang@...el.com>,
        mhcerri@...ux.vnet.ibm.com, leosilva@...ux.vnet.ibm.com,
        pfsmorigo@...ux.vnet.ibm.com, linux-crypto@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [bug] crypto/vmx/p8_ghash memory corruption in 4.8-rc7

On Wed, Sep 28, 2016 at 08:44:52PM +0800, Herbert Xu wrote:
> On Wed, Sep 28, 2016 at 09:38:41AM -0300, Marcelo Cerri wrote:
> > 
> > The patch forces ghash-generic as the fallback. And I don't think that
> > is a big problem if we decide to go by this path.
> 
> Right it should work but could break for example if we ever decide
> to change the exported state structure for ghash and someone unloads
> the ghash-generic module and reloads a new one.
> 

Great! If we check the descsize every time a fallback tfm is allocated
that should be enough to prevent bigger problems such as memory
corruptions.

> > That would be nice because it would allow p8_ghash to keep using a
> > dynamic fallback, but I'm not that is viable. What do you think?
> 
> We did it for SHA because it was desirable to have multiple
> fallbacks, i.e., a generic C version plus an assembly-optimised
> version.
> 
> Not sure whether the same motiviation exists for GHASH.
> 
> > > Otherwise we can go back to allocating just ghash-generic and
> > > also move its data structure into an exported header file.
> > > 
> > 
> > That would make the fix much more simple and it wouldn't require to get
> > the fallback descsize at runtime.
> 
> This is the easiest fix so let's go with this now.  If we ever
> care enough to have multiple fallbacks for GHASH we can always
> revisit this.  The exported format is not exposed to user-space
> so it can always be changed.

Can I move ghash_desc_ctx to a header file under include/crypto/? Or do
you do you prefer to do that?

Maybe include/crypto/internal/hash.h or a new header file
include/crypto/internal/ghash.h ?

> 
> Cheers,
> -- 
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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