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

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Mar 13, 2026 at 10:58:07AM +0800, AlanSong-oc wrote:
> On 3/12/26 12:03, Eric Biggers wrote:
> > 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.
> 
> Sorry for the inconvenience caused by the inability to test provided
> patches, as QEMU currently does not support emulation of the XSHA1 and
> XSHA256 instructions.
> 
> Besides, since the previous patch adding XSHA384 and XSHA512 instruction
> support was not accepted, I would like to ask whether adding emulation
> support for XSHA384 and XSHA512 instructions in QEMU would help the
> crypto community evaluate and accept the corresponding kernel patches.
> 
> > 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.
> 
> Thanks for your suggestions. I will only add XSHA256 instruction support
> for the SHA-256 algorithm in the next version of the patch.

Thanks.  Yes, adding QEMU support for these instructions would be very
helpful. 

- Eric