Re: [PATCH] crypto: x86/aes-gcm: Disable FPU around skcipher_walk_done().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2024-08-03 08:37:05 [+0800], Herbert Xu wrote:
> On Fri, Aug 02, 2024 at 12:23:33PM +0200, Sebastian Andrzej Siewior wrote:
> > kernel_fpu_begin() disables preemption. gcm_crypt() has a
> > skcipher_walk_done() invocation within a preempt disabled section.
> > skcipher_walk_done() can invoke kfree() which requires sleeping locks on
> > PREEMPT_RT and must not be invoked with disabled preemption.
> > 
> > Keep FPU access enabled while skcipher_walk_done() is invoked.
> > 
> > Fixes: b06affb1cb580 ("crypto: x86/aes-gcm - add VAES and AVX512 / AVX10 optimized AES-GCM")
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  arch/x86/crypto/aesni-intel_glue.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
> > index cd37de5ec4046..be92e4c3f9c7f 100644
> > --- a/arch/x86/crypto/aesni-intel_glue.c
> > +++ b/arch/x86/crypto/aesni-intel_glue.c
> > @@ -1403,7 +1403,9 @@ gcm_crypt(struct aead_request *req, int flags)
> >  			aes_gcm_update(key, le_ctr, ghash_acc,
> >  				       walk.src.virt.addr, walk.dst.virt.addr,
> >  				       nbytes, flags);
> > +			kernel_fpu_end();
> >  			err = skcipher_walk_done(&walk, 0);
> > +			kernel_fpu_begin();
> 
> What if the user already did a preempt_disable()? This would still
> be buggy, right?

Yes if it has been done explicitly by preempt_disable(). And I am
looking into explicit case of disabling preemption and trying to get rid
of it if I stumble upon one. This one just popped up on one of my boxes.

> The Crypto API allows this to be called with preemption disabled.
> 
> Cheers,

Sebastian