Re: [PATCH] crypto: add missing kernel_fpu_end() call

[Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>]

Hi,

On Fri, Aug 06, 2021 at 11:07:43AM +0200, Ard Biesheuvel wrote:
> On Fri, 6 Aug 2021 at 11:05, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Fri, 6 Aug 2021 at 10:23, Herbert Xu <herbert@gondor.apana.org.au> wrote:
> > >
> > > On Fri, Jul 30, 2021 at 07:11:55PM +0530, Shreyansh Chouhan wrote:
> > > > xts_crypt() code doesn't call kernel_fpu_end() after calling
> > > > kernel_fpu_begin() if walk.nbytes is 0. Add a call to kernel_fpu_end()
> > > > for this case.
> > > >
> > > > Reported-by: syzbot+20191dc583eff8602d2d@syzkaller.appspotmail.com
> > > > Signed-off-by: Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>
> > > > ---
> > > >  arch/x86/crypto/aesni-intel_glue.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > >
> > > Ard?
> > >
> > > > diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
> > > > index 2144e54a6c89..bd55a0cd7bde 100644
> > > > --- a/arch/x86/crypto/aesni-intel_glue.c
> > > > +++ b/arch/x86/crypto/aesni-intel_glue.c
> > > > @@ -894,6 +894,9 @@ static int xts_crypt(struct skcipher_request *req, bool encrypt)
> > > >                       kernel_fpu_begin();
> > > >       }
> > > >
> > > > +     if (walk.nbytes == 0)
> > > > +             kernel_fpu_end();
> > > > +
> >
> > Don't we end up calling kernel_fpu_end() twice this way if we do enter
> > the while() loop at least once?
> >

Oh ha, we do. I missed that.

> 
> How about the below instead, does that work?
> 

This should work. I will resend the updated patch.

> --- a/arch/x86/crypto/aesni-intel_glue.c
> +++ b/arch/x86/crypto/aesni-intel_glue.c
> @@ -849,7 +849,7 @@ static int xts_crypt(struct skcipher_request *req,
> bool encrypt)
>                 return -EINVAL;
> 
>         err = skcipher_walk_virt(&walk, req, false);
> -       if (err)
> +       if (err || !walk.nbytes)
>                 return err;
> 
>         if (unlikely(tail > 0 && walk.nbytes < walk.total)) {

Thanks a lot for the review.

Regards,
Shreyansh Chouhan