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

From: Herbert Xu
Date: Wed Sep 28 2016 - 08:33:59 EST

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.

Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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