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charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 1 Aug 2023 11:53:52 -0400 Stefan Hajnoczi 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, Alex > > Signed-off-by: Stefan Hajnoczi > --- > drivers/vfio/vfio_iommu_type1.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index ebe0ad31d0b0..d662aa9d1b4b 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -2732,7 +2732,7 @@ static int vfio_iommu_iova_build_caps(struct vfio_iommu *iommu, > 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; > + struct vfio_iommu_type1_info_cap_migration cap_mig = {}; > > cap_mig.header.id = VFIO_IOMMU_TYPE1_INFO_CAP_MIGRATION; > cap_mig.header.version = 1;