linux-kernel - Re: [PATCH 3/4] vfio: use __aligned_u64 in struct vfio_iommu_type1

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Date:   Mon, 14 Aug 2023 14:52:04 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stefan Hajnoczi <stefanha@...hat.com>
Cc:     kvm@...r.kernel.org, "Tian, Kevin" <kevin.tian@...el.com>,
        linux-kernel@...r.kernel.org,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH 3/4] vfio: use __aligned_u64 in struct
 vfio_iommu_type1_info

On Wed, Aug 09, 2023 at 05:02:47PM -0400, Stefan Hajnoczi wrote:
> The memory layout of struct vfio_iommu_type1_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@...pe.ca>
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> ---
>  include/uapi/linux/vfio.h       |  3 ++-
>  drivers/vfio/vfio_iommu_type1.c | 11 ++---------
>  2 files changed, 4 insertions(+), 10 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason