| Message ID | 20230809210248.2898981-5-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio: use __aligned_u64 for ioctl structs | expand |
On Wed, Aug 09, 2023 at 05:02:48PM -0400, Stefan Hajnoczi wrote: > The memory layout of struct vfio_device_ioeventfd 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). > > The code that uses struct vfio_device_ioeventfd already works correctly > when the struct size grows, so only the struct definition needs to be > changed. > > Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > include/uapi/linux/vfio.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Jason
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index 0b5786ec50d8..d61269765bf8 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -794,9 +794,10 @@ struct vfio_device_ioeventfd { #define VFIO_DEVICE_IOEVENTFD_32 (1 << 2) /* 4-byte write */ #define VFIO_DEVICE_IOEVENTFD_64 (1 << 3) /* 8-byte write */ #define VFIO_DEVICE_IOEVENTFD_SIZE_MASK (0xf) - __u64 offset; /* device fd offset of write */ - __u64 data; /* data to be written */ + __aligned_u64 offset; /* device fd offset of write */ + __aligned_u64 data; /* data to be written */ __s32 fd; /* -1 for de-assignment */ + __u32 reserved; }; #define VFIO_DEVICE_IOEVENTFD _IO(VFIO_TYPE, VFIO_BASE + 16)
The memory layout of struct vfio_device_ioeventfd 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). The code that uses struct vfio_device_ioeventfd already works correctly when the struct size grows, so only the struct definition needs to be changed. Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- include/uapi/linux/vfio.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)