Re: [PATCH v3 2/3] lib/crypto: x86/sha1: PHE Extensions optimized SHA1 transform function

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Mar 11, 2026 at 07:37:39PM +0800, AlanSong-oc wrote:
> > I also have to ask: are you sure you need SHA-1 to be optimized at all?
> > SHA-1 has been deprecated for a long time.  Most users have moved to
> > SHA-256 and other stronger algorithms, and those that haven't need to
> > move very soon.  There's little value in adding new optimized code for
> > SHA-1.
> > 
> > How about simplifying your patch to just SHA-256?  Then we can focus on
> > the one that's actually important and not on the deprecated SHA-1.
> 
> It is true that SHA-1 is rarely used by most users today. However, it
> may still be needed in certain scenarios. For those cases, we would like
> to add support for the XHSA1 instruction to accelerate SHA-1.
> 
> Does the crypto community have any plans to remove SHA-1 support in
> recent kernel versions?

It's already possible to build a kernel without SHA-1 support.  SHA-1
has been cryptographically broken and is considered obsolete.
Performance-critical hashing in the kernel already tends to use SHA-256.

These patches already feel marginal, as they are being pushed without
QEMU support, so the community will be unable to test them.  The only
reason I would consider accepting them without QEMU support is because
there was already code in drivers/crypto/ that used these instructions.

It also helps that they are just single instructions.  Though, even with
that I still found a bug in the proposed code as well as errors in the
CPU documentation, as mentioned.  And the drivers/crypto/ implementation
that uses these instructions is broken too, as you're aware of.

Overall, it's clear that platform-specific routines like this are very
risky to maintain without adequate testing.  Yet, correctness is the
first priority in cryptographic code.

So I would suggest that to reduce the risk, we focus on just one
algorithm, SHA-256.  Note that this makes your job easier, as well.

- Eric