On 1/15/2021 5:43 PM, Eric Biggers wrote:
On Fri, Jan 15, 2021 at 04:14:40PM -0800, Dey, Megha wrote:
Hello Megha,

What is the purpose of this separate GHASH module? GHASH is only used
in combination with AES-CTR to produce GCM, and this series already
contains a GCM driver.

Do cores exist that implement PCLMULQDQ but not AES-NI?

If not, I think we should be able to drop this patch (and remove the
existing PCLMULQDQ GHASH driver as well)
AFAIK, dm-verity (authenticated but not encrypted file system) is one use
case for authentication only.

Although I am not sure if GHASH is specifically used for this or SHA?

Also, I do not know of any cores that implement PCLMULQDQ and not AES-NI.

dm-verity only uses unkeyed hash algorithms.  So no, it doesn't use GHASH.

Hmm, I see. If that is the case, I am not aware of any other use case apart from GCM.

I see that the existing GHASH module in the kernel from 2009. I am not sure if there was a use case then, which now is no longer valid.

There many be out-of-tree kernel modules which may be using it but again its only speculation.

So, in the next version should I remove the existing GHASH module? (And of course remove this patch as well?)


- Eric

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