Re: [PATCH] vfio/type1: fix cap_migration information leak

Stefan Hajnoczi
2023-08-01T19:25:05Z

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On Tue, Aug 01, 2023 at 10:31:14AM -0600, Alex Williamson wrote:
> On Tue, 1 Aug 2023 11:53:52 -0400
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> > Fix an information leak where an uninitialized hole in struct
> > vfio_iommu_type1_info_cap_migration on the stack is exposed to userspace.
> >
> > The definition of struct vfio_iommu_type1_info_cap_migration contains a hole as
> > shown in this pahole(1) output:
> >
> > struct vfio_iommu_type1_info_cap_migration {
> > struct vfio_info_cap_header header; /* 0 8 */
> > __u32 flags; /* 8 4 */
> >
> > /* XXX 4 bytes hole, try to pack */
> >
> > __u64 pgsize_bitmap; /* 16 8 */
> > __u64 max_dirty_bitmap_size; /* 24 8 */
> >
> > /* size: 32, cachelines: 1, members: 4 */
> > /* sum members: 28, holes: 1, sum holes: 4 */
> > /* last cacheline: 32 bytes */
> > };
> >
> > The cap_mig variable is filled in without initializing the hole:
> >
> > static int vfio_iommu_migration_build_caps(struct vfio_iommu *iommu,
> > struct vfio_info_cap *caps)
> > {
> > struct vfio_iommu_type1_info_cap_migration cap_mig;
> >
> > cap_mig.header.id = VFIO_IOMMU_TYPE1_INFO_CAP_MIGRATION;
> > cap_mig.header.version = 1;
> >
> > cap_mig.flags = 0;
> > /* support minimum pgsize */
> > cap_mig.pgsize_bitmap = (size_t)1 << __ffs(iommu->pgsize_bitmap);
> > cap_mig.max_dirty_bitmap_size = DIRTY_BITMAP_SIZE_MAX;
> >
> > return vfio_info_add_capability(caps, &cap_mig.header, sizeof(cap_mig));
> > }
> >
> > The structure is then copied to a temporary location on the heap. At this point
> > it's already too late and ioctl(VFIO_IOMMU_GET_INFO) copies it to userspace
> > later:
> >
> > int vfio_info_add_capability(struct vfio_info_cap *caps,
> > struct vfio_info_cap_header *cap, size_t size)
> > {
> > struct vfio_info_cap_header *header;
> >
> > header = vfio_info_cap_add(caps, size, cap->id, cap->version);
> > if (IS_ERR(header))
> > return PTR_ERR(header);
> >
> > memcpy(header + 1, cap + 1, size - sizeof(*header));
> >
> > return 0;
> > }
> >
> > This issue was found by code inspection.
>
> LGTM, but missing:
>
> Fixes: ad721705d09c ("vfio iommu: Add migration capability to report supported features")
>
> I'll give a bit for further comments/reviews and queue it for v6.6 with
> the above update. Thanks,

Great, thanks for squashing in the "Fixes" line that I forgot.

Stefan

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