Re: [PATCH v7 4/5] vfio/pci: implement get_tph and DMA_BUF_TPH feature

[Alex Williamson <alex@shazbot.org>]

On Thu, 11 Jun 2026 16:02:25 -0700
Zhiping Zhang <zhipingz@meta.com> wrote:

> On Thu, Jun 11, 2026 at 1:25 PM <sashiko-bot@kernel.org> wrote:
> >  
> > >  
> > Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> > - [Medium] Unconditional validation of the flag-gated 'ph' parameter can lead to spurious -EINVAL errors, breaking the syscall trust boundary.
> > - [Medium] VFIO_DEVICE_FEATURE_PROBE falsely reports that VFIO_DEVICE_FEATURE_DMA_BUF_TPH is supported even if the hardware lacks TPH support.
> > --
> >
> > commit d57637d667ca6dc95def77a0a5bd339d62d4f506
> > Author: Zhiping Zhang <zhipingz@meta.com>
> >
> > vfio/pci: implement get_tph and DMA_BUF_TPH feature
> >
> > This commit implements dma-buf get_tph for vfio-pci exported dma-bufs and
> > adds the VFIO_DEVICE_FEATURE_DMA_BUF_TPH feature. This allows userspace to
> > publish TPH metadata for a VFIO-owned device. It checks completer support
> > and protects the metadata under dmabuf->resv.
> >  
> > > diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> > > index 1a177ce7de546..0a0705c8dbea6 100644
> > > --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> > > +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c  
> >
> > [ ... ]
> >  
> > > @@ -333,6 +360,71 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> > >       return ret;
> > >  }
> > >
> > > +int vfio_pci_core_feature_dma_buf_tph(struct vfio_pci_core_device *vdev,
> > > +                                   u32 flags,
> > > +                                   struct vfio_device_feature_dma_buf_tph __user *arg,
> > > +                                   size_t argsz)
> > > +{
> > > +     struct vfio_device_feature_dma_buf_tph set_tph;
> > > +     struct vfio_pci_dma_buf *priv;
> > > +     struct dma_buf *dmabuf;
> > > +     u8 comp;
> > > +     int ret;
> > > +
> > > +     ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_SET,
> > > +                              sizeof(set_tph));
> > > +     if (ret != 1)
> > > +             return ret;  
> >
> > [Severity: Medium]
> > vfio_check_feature() returns 0 for VFIO_DEVICE_FEATURE_PROBE, causing an
> > early return of success.
> >
> > Should the hardware capability check (pcie_tph_completer_type) occur before
> > checking the feature flags, to avoid falsely reporting that the feature is
> > supported on devices that lack TPH?
> >  
> 
> Will fix it with a change like below:
>  -     if (ret != 1)
> +     if (ret != 1) {
> +             if (ret == 0 &&
> +                 pcie_tph_completer_type(vdev->pdev) ==
> +                     PCI_EXP_DEVCAP2_TPH_COMP_NONE)
> +                     return -EOPNOTSUPP;
>                 return ret;
> +     }

Typically this is done before the check feature call.  Thanks,

Alex