linux-kernel - Re: [PATCH v4] drivers/vfio: Fix a redundant copy bug

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Date:   Mon, 29 Oct 2018 16:35:12 -0500
From:   Wenwen Wang <wang6495@....edu>
To:     alex.williamson@...hat.com
Cc:     Kangjie Lu <kjlu@....edu>, kvm@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>, aik@...abs.ru,
        david@...son.dropbear.id.au, Wenwen Wang <wang6495@....edu>
Subject: Re: [PATCH v4] drivers/vfio: Fix a redundant copy bug

On Mon, Oct 29, 2018 at 4:32 PM Alex Williamson
<alex.williamson@...hat.com> wrote:
>
> On Mon, 29 Oct 2018 13:56:54 -0500
> Wenwen Wang <wang6495@....edu> wrote:
>
> > Hello,
> >
> > Could you please apply this patch? Thanks!
>
> I'd like to see testing and/or review from David or Alexey since I also
> don't have an environment for spapr/eeh.  We're already late into the
> v4.20 merge window so this is probably v4.21 material.  Thanks,

I see. Thanks for your response, Alex!

> > On Wed, Oct 17, 2018 at 2:18 PM Wenwen Wang <wang6495@....edu> wrote:
> > >
> > > In vfio_spapr_iommu_eeh_ioctl(), if the ioctl command is VFIO_EEH_PE_OP,
> > > the user-space buffer 'arg' is copied to the kernel object 'op' and the
> > > 'argsz' and 'flags' fields of 'op' are checked. If the check fails, an
> > > error code EINVAL is returned. Otherwise, 'op.op' is further checked
> > > through a switch statement to invoke related handlers. If 'op.op' is
> > > VFIO_EEH_PE_INJECT_ERR, the whole user-space buffer 'arg' is copied again
> > > to 'op' to obtain the err information. However, in the following execution
> > > of this case, the fields of 'op', except the field 'err', are actually not
> > > used. That is, the second copy has a redundant part. Therefore, for
> > > performance consideration, the redundant part of the second copy should be
> > > removed.
> > >
> > > This patch removes such a part in the second copy. It only copies from
> > > 'err.type' to 'err.mask', which is exactly required by the
> > > VFIO_EEH_PE_INJECT_ERR op.
> > >
> > > Signed-off-by: Wenwen Wang <wang6495@....edu>
> > > ---
> > >  drivers/vfio/vfio_spapr_eeh.c | 9 ++++++---
> > >  1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/vfio/vfio_spapr_eeh.c b/drivers/vfio/vfio_spapr_eeh.c
> > > index 38edeb4..66634c6 100644
> > > --- a/drivers/vfio/vfio_spapr_eeh.c
> > > +++ b/drivers/vfio/vfio_spapr_eeh.c
> > > @@ -37,6 +37,7 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group,
> > >         struct eeh_pe *pe;
> > >         struct vfio_eeh_pe_op op;
> > >         unsigned long minsz;
> > > +       unsigned long start, end;
> > >         long ret = -EINVAL;
> > >
> > >         switch (cmd) {
> > > @@ -86,10 +87,12 @@ long vfio_spapr_iommu_eeh_ioctl(struct iommu_group *group,
> > >                         ret = eeh_pe_configure(pe);
> > >                         break;
> > >                 case VFIO_EEH_PE_INJECT_ERR:
> > > -                       minsz = offsetofend(struct vfio_eeh_pe_op, err.mask);
> > > -                       if (op.argsz < minsz)
> > > +                       start = offsetof(struct vfio_eeh_pe_op, err.type);
> > > +                       end = offsetofend(struct vfio_eeh_pe_op, err.mask);
> > > +                       if (op.argsz < end)
> > >                                 return -EINVAL;
> > > -                       if (copy_from_user(&op, (void __user *)arg, minsz))
> > > +                       if (copy_from_user(&op.err, (char __user *)arg +
> > > +                                               start, end - start))
> > >                                 return -EFAULT;
> > >
> > >                         ret = eeh_pe_inject_err(pe, op.err.type, op.err.func,
> > > --
> > > 2.7.4
> > >
>