From: Stefan Hajnoczi > Sent: 29 August 2023 19:27 > > v2: > - Rebased onto https://github.com/awilliam/linux-vfio.git next to get the > vfio_iommu_type1_info pad field [Kevin] > - Fixed min(minsz, sizeof(dmabuf)) -> min(dmabuf.argsz, sizeof(dmabuf)) [Jason, Kevin] You managed to use min_t() instead of fixing the types to match. > - Squashed Patch 3 (vfio_iommu_type1_info) into Patch 1 since it is trivial now > that the padding field is already there. > > Jason Gunthorpe <jgg@xxxxxxxxxx> pointed out that u64 VFIO ioctl struct fields > have architecture-dependent alignment. iommufd already uses __aligned_u64 to > avoid this problem. > > See the __aligned_u64 typedef in <uapi/linux/types.h> for details on why it is > a good idea for kernel<->user interfaces. > > This series modifies the VFIO ioctl structs to use __aligned_u64. Some of the > changes preserve the existing memory layout on all architectures, so I put them > together into the first patch. The remaining patches are for structs where > explanation is necessary about why changing the memory layout does not break > the uapi. But you are extending a field in the middle of the uapi structure. This completely breaks any applications. You could add code to detect the length of the user-provided structure and use the correct kernel structure that matches the length of the user-provided one. That needs the opposite of __aligned_u64 - a 64bit integer with 32bit alignment on x64-64. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
