On Fri, 8 Nov 2024 04:17:41 -0800
Yi Liu <yi.l.liu@xxxxxxxxx> wrote:
> This generalizes the logic of copying user data when the user struct
> Have new fields introduced. The helpers can be used by the vfio uapis
> that have the argsz and flags fields in the beginning 8 bytes.
>
> As an example, the vfio_device_{at|de}tach_iommufd_pt paths are updated
> to use the helpers.
>
> The flags may be defined to mark a new field in the structure, reuse
> reserved fields, or special handling of an existing field. The extended
> size would differ for different flags. Each user API that wants to use
> the generalized helpers should define an array to store the corresponding
> extended sizes for each defined flag.
>
> For example, we start out with the below, minsz is 12.
>
> struct vfio_foo_struct {
> __u32 argsz;
> __u32 flags;
> __u32 pt_id;
> };
>
> And then here it becomes:
>
> struct vfio_foo_struct {
> __u32 argsz;
> __u32 flags;
> #define VFIO_FOO_STRUCT_PASID (1 << 0)
> __u32 pt_id;
> __u32 pasid;
> };
>
> The array is { 16 }.
>
> If the next flag is simply related to the processing of @pt_id and
> doesn't require @pasid, then the extended size of the new flag is
> 12. The array become { 16, 12 }
>
> struct vfio_foo_struct {
> __u32 argsz;
> __u32 flags;
> #define VFIO_FOO_STRUCT_PASID (1 << 0)
> #define VFIO_FOO_STRUCT_SPECICAL_PTID (1 << 1)
> __u32 pt_id;
> __u32 pasid;
> };
>
> Similarly, rather than adding new field, we might have reused a previously
> reserved field, for instance what if we already expanded the structure
> as the below, array is already { 24 }.
>
> struct vfio_foo_struct {
> __u32 argsz;
> __u32 flags;
> #define VFIO_FOO_STRUCT_XXX (1 << 0)
> __u32 pt_id;
> __u32 reserved;
> __u64 xxx;
> };
>
> If we then want to add @pasid, we might really prefer to take advantage
> of that reserved field and the array becomes { 24, 16 }.
>
> struct vfio_foo_struct {
> __u32 argsz;
> __u32 flags;
> #define VFIO_FOO_STRUCT_XXX (1 << 0)
> #define VFIO_FOO_STRUCT_PASID (1 << 1)
> __u32 pt_id;
> __u32 reserved;
I think this was supposed to be s/reserved/pasid/
> __u64 xxx;
> };
>
> Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
> drivers/vfio/device_cdev.c | 81 +++++++++++++-------------------------
> drivers/vfio/vfio.h | 18 +++++++++
> drivers/vfio/vfio_main.c | 55 ++++++++++++++++++++++++++
> 3 files changed, 100 insertions(+), 54 deletions(-)
>
> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index 4519f482e212..35c7664b9a97 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -159,40 +159,33 @@ void vfio_df_unbind_iommufd(struct vfio_device_file *df)
> vfio_device_unblock_group(device);
> }
>
> +#define VFIO_ATTACH_FLAGS_MASK VFIO_DEVICE_ATTACH_PASID
> +static unsigned long
> +vfio_attach_xends[ilog2(VFIO_ATTACH_FLAGS_MASK) + 1] = {
> + XEND_SIZE(VFIO_DEVICE_ATTACH_PASID,
> + struct vfio_device_attach_iommufd_pt, pasid),
> +};
> +
> +#define VFIO_DETACH_FLAGS_MASK VFIO_DEVICE_DETACH_PASID
> +static unsigned long
> +vfio_detach_xends[ilog2(VFIO_DETACH_FLAGS_MASK) + 1] = {
> + XEND_SIZE(VFIO_DEVICE_DETACH_PASID,
> + struct vfio_device_detach_iommufd_pt, pasid),
> +};
> +
> int vfio_df_ioctl_attach_pt(struct vfio_device_file *df,
> struct vfio_device_attach_iommufd_pt __user *arg)
> {
> struct vfio_device_attach_iommufd_pt attach;
> struct vfio_device *device = df->device;
> - unsigned long minsz, xend = 0;
> int ret;
>
> - minsz = offsetofend(struct vfio_device_attach_iommufd_pt, pt_id);
> -
> - if (copy_from_user(&attach, arg, minsz))
> - return -EFAULT;
> -
> - if (attach.argsz < minsz)
> - return -EINVAL;
> -
> - if (attach.flags & (~VFIO_DEVICE_ATTACH_PASID))
> - return -EINVAL;
> -
> - if (attach.flags & VFIO_DEVICE_ATTACH_PASID)
> - xend = offsetofend(struct vfio_device_attach_iommufd_pt, pasid);
> -
> - /*
> - * xend may be equal to minsz if a flag is defined for reusing a
> - * reserved field or a special usage of an existing field.
> - */
> - if (xend > minsz) {
> - if (attach.argsz < xend)
> - return -EINVAL;
> -
> - if (copy_from_user((void *)&attach + minsz,
> - (void __user *)arg + minsz, xend - minsz))
> - return -EFAULT;
> - }
> + ret = vfio_copy_user_data((void __user *)arg, &attach,
> + struct vfio_device_attach_iommufd_pt,
> + pt_id, VFIO_ATTACH_FLAGS_MASK,
> + vfio_attach_xends);
> + if (ret)
> + return ret;
>
> if ((attach.flags & VFIO_DEVICE_ATTACH_PASID) &&
> !device->ops->pasid_attach_ioas)
> @@ -227,34 +220,14 @@ int vfio_df_ioctl_detach_pt(struct vfio_device_file *df,
> {
> struct vfio_device_detach_iommufd_pt detach;
> struct vfio_device *device = df->device;
> - unsigned long minsz, xend = 0;
> -
> - minsz = offsetofend(struct vfio_device_detach_iommufd_pt, flags);
> -
> - if (copy_from_user(&detach, arg, minsz))
> - return -EFAULT;
> -
> - if (detach.argsz < minsz)
> - return -EINVAL;
> -
> - if (detach.flags & (~VFIO_DEVICE_DETACH_PASID))
> - return -EINVAL;
> -
> - if (detach.flags & VFIO_DEVICE_DETACH_PASID)
> - xend = offsetofend(struct vfio_device_detach_iommufd_pt, pasid);
> -
> - /*
> - * xend may be equal to minsz if a flag is defined for reusing a
> - * reserved field or a special usage of an existing field.
> - */
> - if (xend > minsz) {
> - if (detach.argsz < xend)
> - return -EINVAL;
> + int ret;
>
> - if (copy_from_user((void *)&detach + minsz,
> - (void __user *)arg + minsz, xend - minsz))
> - return -EFAULT;
> - }
> + ret = vfio_copy_user_data((void __user *)arg, &detach,
> + struct vfio_device_detach_iommufd_pt,
> + flags, VFIO_DETACH_FLAGS_MASK,
> + vfio_detach_xends);
> + if (ret)
> + return ret;
>
> if ((detach.flags & VFIO_DEVICE_DETACH_PASID) &&
> !device->ops->pasid_detach_ioas)
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 50128da18bca..87bed550c46e 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -34,6 +34,24 @@ void vfio_df_close(struct vfio_device_file *df);
> struct vfio_device_file *
> vfio_allocate_device_file(struct vfio_device *device);
>
> +int vfio_copy_from_user(void *buffer, void __user *arg,
> + unsigned long minsz, u32 flags_mask,
> + unsigned long *xend_array);
> +
> +#define vfio_copy_user_data(_arg, _local_buffer, _struct, _min_last, \
> + _flags_mask, _xend_array) \
> + vfio_copy_from_user(_local_buffer, _arg, \
> + offsetofend(_struct, _min_last) + \
> + BUILD_BUG_ON_ZERO(offsetof(_struct, argsz) != \
> + 0) + \
> + BUILD_BUG_ON_ZERO(offsetof(_struct, flags) != \
> + sizeof(u32)), \
> + _flags_mask, _xend_array)
> +
> +#define XEND_SIZE(_flag, _struct, _xlast) \
> + [ilog2(_flag)] = offsetofend(_struct, _xlast) + \
> + BUILD_BUG_ON_ZERO(_flag == 0) \
> +
> extern const struct file_operations vfio_device_fops;
>
> #ifdef CONFIG_VFIO_NOIOMMU
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index a5a62d9d963f..c61336ea5123 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -1694,6 +1694,61 @@ int vfio_dma_rw(struct vfio_device *device, dma_addr_t iova, void *data,
> }
> EXPORT_SYMBOL(vfio_dma_rw);
>
> +/**
> + * vfio_copy_from_user - Copy the user struct that may have extended fields
> + *
> + * @buffer: The local buffer to store the data copied from user
> + * @arg: The user buffer pointer
> + * @minsz: The minimum size of the user struct
> + * @flags_mask: The combination of all the falgs defined
> + * @xend_array: The array that stores the xend size for set flags.
> + *
> + * This helper requires the user struct put the argsz and flags fields in
> + * the first 8 bytes.
> + *
> + * Return 0 for success, otherwise -errno
> + */
> +int vfio_copy_from_user(void *buffer, void __user *arg,
This should probably be prefixed with an underscore and note that
callers should use the wrapper function to impose the parameter
checking.
> + unsigned long minsz, u32 flags_mask,
> + unsigned long *xend_array)
> +{
> + unsigned long xend = minsz;
> + struct user_header {
> + u32 argsz;
> + u32 flags;
> + } *header;
> + unsigned long flags;
> + u32 flag;
> +
> + if (copy_from_user(buffer, arg, minsz))
> + return -EFAULT;
> +
> + header = (struct user_header *)buffer;
> + if (header->argsz < minsz)
> + return -EINVAL;
> +
> + if (header->flags & ~flags_mask)
> + return -EINVAL;
I'm already wrestling with whether this is an over engineered solution
to remove a couple dozen lines of mostly duplicate logic between attach
and detach, but a couple points that could make it more versatile:
(1) Test xend_array here:
if (!xend_array)
return 0;
(2) Return ssize_t/-errno for the caller to know the resulting copy
size.
> +
> + /* Loop each set flag to decide the xend */
> + flags = header->flags;
> + for_each_set_bit(flag, &flags, BITS_PER_TYPE(u32)) {
> + if (xend_array[flag] > xend)
> + xend = xend_array[flag];
Can we craft a BUILD_BUG in the wrapper to test that xend_array is at
least long enough to match the highest bit in flags? Thanks,
Alex
> + }
> +
> + if (xend > minsz) {
> + if (header->argsz < xend)
> + return -EINVAL;
> +
> + if (copy_from_user(buffer + minsz,
> + arg + minsz, xend - minsz))
> + return -EFAULT;
> + }
> +
> + return 0;
> +}
> +
> /*
> * Module/class support
> */
