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

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Message-ID: <CAAa=b7dE=6obq4nABsyo84iA1CTOcLVCAuUxHDYfSCimzc12eA@mail.gmail.com>
Date:   Mon, 29 Oct 2018 13:56:54 -0500
From:   Wenwen Wang <wang6495@....edu>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Kangjie Lu <kjlu@....edu>, alex.williamson@...hat.com,
        kvm@...r.kernel.org, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drivers/vfio: Fix a redundant copy bug

Hello,

Could you please apply this patch? Thanks!

Wenwen

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
>