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

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Message-ID: <20160928123318.GB20839@gondor.apana.org.au>
Date:   Wed, 28 Sep 2016 20:33:18 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Marcelo Cerri <marcelo.cerri@...onical.com>
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 09:28:44AM -0300, Marcelo Cerri wrote:
>
> The big difference between p8_ghash and padlock_sha1 is that
> padlock_sha1 defines alg->statesize as sizeof(struct sha1_state), which
> is the descsize value used by sha1_generic. This probably works but
> it's also wrong because the padlock_sha1 driver does not ensures that
> sha1_generic is always used.

It should work because all our SHA implementations use the same
export format.  This is not necessarily the case for GHASH though.

> So, one solution is to hardcode ghash-generic as the fallback algorithm
> and update the descsize direct in its shash_alg structure. There's only
> one problem with that. ghash-generic desc type (struct ghash_desc_ctx)
> is not available for vmx_crypto at compile type, the type is defined
> directly in crypto/ghash-generic.c. That's the reason I added a function
> to get the fallback desc size at runtime in the patch I wrote as a prove
> of concept.

The problem with your patch is that there is no guarantee that
you will get the same algorithm every time you allocate a fallback.
Someone may have loaded a new module for example.

So I think the safe approach is to stick with ghash-generic and
expose its state data structure in a header file.

Thanks,
-- 
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