Re: [PATCH] crypto: arm64/ghash - Fix incorrect output from ghash-neon

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Dec 10, 2025 at 06:31:44PM +0900, Ard Biesheuvel wrote:
> On Wed, 10 Dec 2025 at 18:22, Diederik de Haas <diederik@cknow-tech.com> wrote:
> >
> > On Tue Dec 9, 2025 at 11:34 PM CET, Eric Biggers wrote:
> > > Commit 9a7c987fb92b ("crypto: arm64/ghash - Use API partial block
> > > handling") made ghash_finup() pass the wrong buffer to
> > > ghash_do_simd_update().  As a result, ghash-neon now produces incorrect
> > > outputs when the message length isn't divisible by 16 bytes.  Fix this.
> >
> > I was hoping to not have to do a 'git bisect', but this is much better
> > :-D I can confirm that this patch fixes the error I was seeing, so
> >
> > Tested-by: Diederik de Haas <diederik@cknow-tech.com>
> >
> > > (I didn't notice this earlier because this code is reached only on CPUs
> > > that support NEON but not PMULL.  I haven't yet found a way to get
> > > qemu-system-aarch64 to emulate that configuration.)
> >
> > https://www.qemu.org/docs/master/system/arm/raspi.html indicates it can
> > emulate various Raspberry Pi models. I've only tested it with RPi 3B+
> > (bc of its wifi+bt chip), but I wouldn't be surprised if all RPi models
> > would have this problem? Dunno if QEMU emulates that though.
> >
> 
> All 64-bit RPi models except the RPi5 are affected by this, as those
> do not implement the crypto extensions. So I would expect QEMU to do
> the same.
> 
> It would be nice, though, if we could emulate this on the mach-virt
> machine model too. It should be fairly trivial to do, so if there is
> demand for this I can look into it.

I'm definitely interested in it.  I'm already testing multiple "-cpu"
options, and it's easy to add more.

With qemu-system-aarch64 I'm currently only using "-M virt", since the
other machine models I've tried don't boot with arm64 defconfig,
including "-M raspi3b" and "-M raspi4b".

There may be some tricks I'm missing.  Regardless, expanding the
selection of available CPUs for "-M virt" would be helpful.  Either by
adding "real" CPUs that have "interesting" combinations of features, or
by just allowing turning features off like
"-cpu max,aes=off,pmull=off,sha256=off".  (Certain features like sve can
already be turned off in that way, but not the ones relevant to us.)

- Eric