| Message ID | 20230809210248.2898981-3-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio: use __aligned_u64 for ioctl structs | expand |
> From: Stefan Hajnoczi <stefanha@redhat.com> > Sent: Thursday, August 10, 2023 5:03 AM > > The memory layout of struct vfio_device_gfx_plane_info is > architecture-dependent due to a u64 field and a struct size that is not > a multiple of 8 bytes: > - On x86_64 the struct size is padded to a multiple of 8 bytes. > - On x32 the struct size is only a multiple of 4 bytes, not 8. > - Other architectures may vary. > > Use __aligned_u64 to make memory layout consistent. This reduces the > chance of holes that result in an information leak and the chance that I didn't quite get this. The leak example [1] from your earlier fix is really not caused by the use of __u64. Instead it's a counter example that on x32 there is no hole with 4byte alignment for __u64. I'd remove the hole part and just keep the compat reason. [1] https://lore.kernel.org/lkml/20230801103114.757d7992.alex.williamson@redhat.com/T/ > @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device > *vfio_dev, unsigned int cmd, > if (dmabuf.argsz < minsz) > return -EINVAL; > > + minsz = min(minsz, sizeof(dmabuf)); > + Is there a case where minsz could be greater than sizeof(dmabuf)?
On Thu, Aug 10, 2023 at 03:22:56AM +0000, Tian, Kevin wrote: > > From: Stefan Hajnoczi <stefanha@redhat.com> > > Sent: Thursday, August 10, 2023 5:03 AM > > > > The memory layout of struct vfio_device_gfx_plane_info is > > architecture-dependent due to a u64 field and a struct size that is not > > a multiple of 8 bytes: > > - On x86_64 the struct size is padded to a multiple of 8 bytes. > > - On x32 the struct size is only a multiple of 4 bytes, not 8. > > - Other architectures may vary. > > > > Use __aligned_u64 to make memory layout consistent. This reduces the > > chance of holes that result in an information leak and the chance that > > I didn't quite get this. The leak example [1] from your earlier fix is really > not caused by the use of __u64. Instead it's a counter example that on > x32 there is no hole with 4byte alignment for __u64. > > I'd remove the hole part and just keep the compat reason. > > [1] https://lore.kernel.org/lkml/20230801103114.757d7992.alex.williamson@redhat.com/T/ Okay. > > > @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device > > *vfio_dev, unsigned int cmd, > > if (dmabuf.argsz < minsz) > > return -EINVAL; > > > > + minsz = min(minsz, sizeof(dmabuf)); > > + > > Is there a case where minsz could be greater than sizeof(dmabuf)? Thanks for spotting this, it's a bug in the patch. It should be min(dmabuf.argsz, sizeof(dmabuf)). Stefan
On Wed, Aug 09, 2023 at 05:02:46PM -0400, Stefan Hajnoczi wrote: > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c > index de675d799c7d..ffab3536dc8a 100644 > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > @@ -1382,7 +1382,7 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, > intel_gvt_reset_vgpu(vgpu); > return 0; > } else if (cmd == VFIO_DEVICE_QUERY_GFX_PLANE) { > - struct vfio_device_gfx_plane_info dmabuf; > + struct vfio_device_gfx_plane_info dmabuf = {}; > int ret = 0; > > minsz = offsetofend(struct vfio_device_gfx_plane_info, > @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, > if (dmabuf.argsz < minsz) > return -EINVAL; > > + minsz = min(minsz, sizeof(dmabuf)); > + Huh? minsz = min(sizeof(dmabuf), dmabuf.argsz) > ret = intel_vgpu_query_plane(vgpu, &dmabuf); > if (ret != 0) > return ret; > diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c > index c6c6b5d26670..ee42a780041f 100644 > --- a/samples/vfio-mdev/mbochs.c > +++ b/samples/vfio-mdev/mbochs.c > @@ -1262,7 +1262,7 @@ static long mbochs_ioctl(struct vfio_device *vdev, unsigned int cmd, > > case VFIO_DEVICE_QUERY_GFX_PLANE: > { > - struct vfio_device_gfx_plane_info plane; > + struct vfio_device_gfx_plane_info plane = {}; > > minsz = offsetofend(struct vfio_device_gfx_plane_info, > region_index); > @@ -1273,11 +1273,13 @@ static long mbochs_ioctl(struct vfio_device *vdev, unsigned int cmd, > if (plane.argsz < minsz) > return -EINVAL; > > + outsz = min_t(unsigned long, plane.argsz, sizeof(plane)); > + This one is right Jason
On Mon, Aug 14, 2023 at 02:50:40PM -0300, Jason Gunthorpe wrote: > On Wed, Aug 09, 2023 at 05:02:46PM -0400, Stefan Hajnoczi wrote: > > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c > > index de675d799c7d..ffab3536dc8a 100644 > > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > > @@ -1382,7 +1382,7 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, > > intel_gvt_reset_vgpu(vgpu); > > return 0; > > } else if (cmd == VFIO_DEVICE_QUERY_GFX_PLANE) { > > - struct vfio_device_gfx_plane_info dmabuf; > > + struct vfio_device_gfx_plane_info dmabuf = {}; > > int ret = 0; > > > > minsz = offsetofend(struct vfio_device_gfx_plane_info, > > @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, > > if (dmabuf.argsz < minsz) > > return -EINVAL; > > > > + minsz = min(minsz, sizeof(dmabuf)); > > + > > Huh? > > minsz = min(sizeof(dmabuf), dmabuf.argsz) Thanks for catching this. I will fix it in the next revision. Stefan
On Thu, Aug 10, 2023 at 03:22:56AM +0000, Tian, Kevin wrote: > > From: Stefan Hajnoczi <stefanha@redhat.com> > > Sent: Thursday, August 10, 2023 5:03 AM > > > > The memory layout of struct vfio_device_gfx_plane_info is > > architecture-dependent due to a u64 field and a struct size that is not > > a multiple of 8 bytes: > > - On x86_64 the struct size is padded to a multiple of 8 bytes. > > - On x32 the struct size is only a multiple of 4 bytes, not 8. > > - Other architectures may vary. > > > > Use __aligned_u64 to make memory layout consistent. This reduces the > > chance of holes that result in an information leak and the chance that > > I didn't quite get this. The leak example [1] from your earlier fix is really > not caused by the use of __u64. Instead it's a counter example that on > x32 there is no hole with 4byte alignment for __u64. > > I'd remove the hole part and just keep the compat reason. > > [1] https://lore.kernel.org/lkml/20230801103114.757d7992.alex.williamson@redhat.com/T/ Sounds good. > > > @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device > > *vfio_dev, unsigned int cmd, > > if (dmabuf.argsz < minsz) > > return -EINVAL; > > > > + minsz = min(minsz, sizeof(dmabuf)); > > + > > Is there a case where minsz could be greater than sizeof(dmabuf)? I'll fix this in the next revision (it should be dmabuf.argsz). Stefan
From: Stefan Hajnoczi > Sent: 09 August 2023 22:03 > > The memory layout of struct vfio_device_gfx_plane_info is > architecture-dependent due to a u64 field and a struct size that is not > a multiple of 8 bytes: > - On x86_64 the struct size is padded to a multiple of 8 bytes. > - On x32 the struct size is only a multiple of 4 bytes, not 8. > - Other architectures may vary. > > Use __aligned_u64 to make memory layout consistent. This reduces the > chance of holes that result in an information leak and the chance that > 32-bit userspace on a 64-bit kernel breakage. Isn't the hole likely to cause an information leak? Forcing it to be there doesn't make any difference. I'd add an explicit pad as well. It is a shame there isn't an __attribute__(()) to error padded structures. > > This patch increases the struct size on x32 but this is safe because of > the struct's argsz field. The kernel may grow the struct as long as it > still supports smaller argsz values from userspace (e.g. applications > compiled against older kernel headers). Doesn't changing the offset of later fields break compatibility? The size field (probably) only lets you extend the structure. Oh, for sanity do min(variable, constant). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On Tue, Aug 15, 2023 at 03:23:50PM +0000, David Laight wrote: > From: Stefan Hajnoczi > > Sent: 09 August 2023 22:03 > > > > The memory layout of struct vfio_device_gfx_plane_info is > > architecture-dependent due to a u64 field and a struct size that is not > > a multiple of 8 bytes: > > - On x86_64 the struct size is padded to a multiple of 8 bytes. > > - On x32 the struct size is only a multiple of 4 bytes, not 8. > > - Other architectures may vary. > > > > Use __aligned_u64 to make memory layout consistent. This reduces the > > chance of holes that result in an information leak and the chance that > > 32-bit userspace on a 64-bit kernel breakage. > > Isn't the hole likely to cause an information leak? > Forcing it to be there doesn't make any difference. > I'd add an explicit pad as well. Yes, Kevin had a similar comment about this text. What I meant was that it's safest to have a single memory layout across all architectures (with explicit padding) so that there are no surprises. I'm going to remove the statement about information leaks because it's confusing. > > It is a shame there isn't an __attribute__(()) to error padded structures. > > > > > This patch increases the struct size on x32 but this is safe because of > > the struct's argsz field. The kernel may grow the struct as long as it > > still supports smaller argsz values from userspace (e.g. applications > > compiled against older kernel headers). > > Doesn't changing the offset of later fields break compatibility? > The size field (probably) only lets you extend the structure. Yes, that would break compatibility but I don't see any changes in this patch series that modifies the offsets of later fields. Have I missed something? > Oh, for sanity do min(variable, constant). Can you elaborate? Thanks, Stefan
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index b1dfcf3b7665..45db62d74064 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -746,7 +746,7 @@ struct vfio_device_gfx_plane_info { __u32 drm_plane_type; /* type of plane: DRM_PLANE_TYPE_* */ /* out */ __u32 drm_format; /* drm format of plane */ - __u64 drm_format_mod; /* tiled mode */ + __aligned_u64 drm_format_mod; /* tiled mode */ __u32 width; /* width of plane */ __u32 height; /* height of plane */ __u32 stride; /* stride of plane */ @@ -759,6 +759,7 @@ struct vfio_device_gfx_plane_info { __u32 region_index; /* region index */ __u32 dmabuf_id; /* dma-buf id */ }; + __u32 reserved; }; #define VFIO_DEVICE_QUERY_GFX_PLANE _IO(VFIO_TYPE, VFIO_BASE + 14) diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c index de675d799c7d..ffab3536dc8a 100644 --- a/drivers/gpu/drm/i915/gvt/kvmgt.c +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c @@ -1382,7 +1382,7 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, intel_gvt_reset_vgpu(vgpu); return 0; } else if (cmd == VFIO_DEVICE_QUERY_GFX_PLANE) { - struct vfio_device_gfx_plane_info dmabuf; + struct vfio_device_gfx_plane_info dmabuf = {}; int ret = 0; minsz = offsetofend(struct vfio_device_gfx_plane_info, @@ -1392,6 +1392,8 @@ static long intel_vgpu_ioctl(struct vfio_device *vfio_dev, unsigned int cmd, if (dmabuf.argsz < minsz) return -EINVAL; + minsz = min(minsz, sizeof(dmabuf)); + ret = intel_vgpu_query_plane(vgpu, &dmabuf); if (ret != 0) return ret; diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c index c6c6b5d26670..ee42a780041f 100644 --- a/samples/vfio-mdev/mbochs.c +++ b/samples/vfio-mdev/mbochs.c @@ -1262,7 +1262,7 @@ static long mbochs_ioctl(struct vfio_device *vdev, unsigned int cmd, case VFIO_DEVICE_QUERY_GFX_PLANE: { - struct vfio_device_gfx_plane_info plane; + struct vfio_device_gfx_plane_info plane = {}; minsz = offsetofend(struct vfio_device_gfx_plane_info, region_index); @@ -1273,11 +1273,13 @@ static long mbochs_ioctl(struct vfio_device *vdev, unsigned int cmd, if (plane.argsz < minsz) return -EINVAL; + outsz = min_t(unsigned long, plane.argsz, sizeof(plane)); + ret = mbochs_query_gfx_plane(mdev_state, &plane); if (ret) return ret; - if (copy_to_user((void __user *)arg, &plane, minsz)) + if (copy_to_user((void __user *)arg, &plane, outsz)) return -EFAULT; return 0; diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c index a62ea11e20ec..1500b120de04 100644 --- a/samples/vfio-mdev/mdpy.c +++ b/samples/vfio-mdev/mdpy.c @@ -591,7 +591,7 @@ static long mdpy_ioctl(struct vfio_device *vdev, unsigned int cmd, case VFIO_DEVICE_QUERY_GFX_PLANE: { - struct vfio_device_gfx_plane_info plane; + struct vfio_device_gfx_plane_info plane = {}; minsz = offsetofend(struct vfio_device_gfx_plane_info, region_index); @@ -602,6 +602,8 @@ static long mdpy_ioctl(struct vfio_device *vdev, unsigned int cmd, if (plane.argsz < minsz) return -EINVAL; + minsz = min_t(unsigned long, plane.argsz, sizeof(plane)); + ret = mdpy_query_gfx_plane(mdev_state, &plane); if (ret) return ret;
The memory layout of struct vfio_device_gfx_plane_info is architecture-dependent due to a u64 field and a struct size that is not a multiple of 8 bytes: - On x86_64 the struct size is padded to a multiple of 8 bytes. - On x32 the struct size is only a multiple of 4 bytes, not 8. - Other architectures may vary. Use __aligned_u64 to make memory layout consistent. This reduces the chance of holes that result in an information leak and the chance that 32-bit userspace on a 64-bit kernel breakage. This patch increases the struct size on x32 but this is safe because of the struct's argsz field. The kernel may grow the struct as long as it still supports smaller argsz values from userspace (e.g. applications compiled against older kernel headers). Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- include/uapi/linux/vfio.h | 3 ++- drivers/gpu/drm/i915/gvt/kvmgt.c | 4 +++- samples/vfio-mdev/mbochs.c | 6 ++++-- samples/vfio-mdev/mdpy.c | 4 +++- 4 files changed, 12 insertions(+), 5 deletions(-)