Re: [PATCH] vfio: align capability structures

Stefan Hajnoczi
2023-08-09T20:33:03Z

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On Tue, Aug 08, 2023 at 08:29:25PM -0300, Jason Gunthorpe wrote:
> On Thu, Aug 03, 2023 at 03:18:23PM -0600, Alex Williamson wrote:
>
> > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> > index 902f06e52c48..2d074cbd371d 100644
> > --- a/drivers/vfio/vfio_main.c
> > +++ b/drivers/vfio/vfio_main.c
> > @@ -1362,6 +1362,8 @@ struct vfio_info_cap_header *vfio_info_cap_add(struct vfio_info_cap *caps,
> > void *buf;
> > struct vfio_info_cap_header *header, *tmp;
> >
> > + size = ALIGN(size, sizeof(u64));
> > +
> > buf = krealloc(caps->buf, caps->size + size, GFP_KERNEL);
> > if (!buf) {
> > kfree(caps->buf);
> > @@ -1395,6 +1397,8 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
> > struct vfio_info_cap_header *tmp;
> > void *buf = (void *)caps->buf;
> >
> > + WARN_ON(!IS_ALIGNED(offset, sizeof(u64)));
> > +
> > for (tmp = buf; tmp->next; tmp = buf + tmp->next - offset)
> > tmp->next += offset;
> > }
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index fa06e3eb4955..fd2761841ffe 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -217,6 +217,7 @@ struct vfio_device_info {
> > __u32 num_regions; /* Max region index + 1 */
> > __u32 num_irqs; /* Max IRQ index + 1 */
> > __u32 cap_offset; /* Offset within info struct of first cap */
> > + __u32 pad; /* Size must be aligned for caps */
> > };
> > #define VFIO_DEVICE_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 7)
> >
> > @@ -1444,6 +1445,7 @@ struct vfio_iommu_type1_info {
> > #define VFIO_IOMMU_INFO_CAPS (1 << 1) /* Info supports caps */
> > __u64 iova_pgsizes; /* Bitmap of supported page sizes */
> > __u32 cap_offset; /* Offset within info struct of first cap */
> > + __u32 pad; /* Size must be aligned for caps */
> > };
>
> IMHO this is partially being caused by not using __aligned_u64 for the
> other __u64's in the same struct..
>
> Both of these structs have u64s in them and many arches will
> automatically add the above padding. __aligned_u64 will force the
> reset to do it, and then making padding explicit as you have done will
> make it really true.
>
> This is a subtle x64/x32 compatability issue also. It is probably best
> just to do the change across the whole header file.

I will send a separate series that switches the struct definitions to
__aligned_u64.

> Please also include the matching hunk for iommufd:
>
> --- a/drivers/iommu/iommufd/vfio_compat.c
> +++ b/drivers/iommu/iommufd/vfio_compat.c
> @@ -483,6 +483,8 @@ static int iommufd_vfio_iommu_get_info(struct iommufd_ctx *ictx,
> rc = cap_size;
> goto out_put;
> }
> + cap_size = ALIGN(cap_size, sizeof(u64));
> +
> if (last_cap && info.argsz >= total_cap_size &&
> put_user(total_cap_size, &last_cap->next)) {
> rc = -EFAULT;

Okay, will fix.

Stefan

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