Re: [PATCH 2/2] pci: Update VPD size with correct length

[Alexander Duyck]

On Wed, Dec 16, 2015 at 11:59 PM, Hannes Reinecke <hare@xxxxxxx> wrote:
> PCI-2.2 VPD entries have a maximum size of 32k, but might actually
> be smaller than that. To figure out the actual size one has to read
> the VPD area until the 'end marker' is reached.
> Trying to read VPD data beyond that marker results in 'interesting'
> effects, from simple read errors to crashing the card. And to make
> matters worse not every PCI card implements this properly, leaving
> us with no 'end' marker or even completely invalid data.
> This path modifies the size of the VPD attribute to the available
> size, and disables the VPD attribute altogether if no valid data
> could be read.
>
> Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
> Cc: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
> ---
>  drivers/pci/access.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 59ac36f..0a647b1 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -475,6 +475,56 @@ static const struct pci_vpd_ops pci_vpd_f0_ops = {
>         .release = pci_vpd_pci22_release,
>  };
>
> +/**
> + * pci_vpd_size - determine actual size of Vital Product Data
> + * @dev:       pci device struct
> + * @old_size:  current assumed size, also maximum allowed size
> + *

"old_siz"e was dropped so you can remove this line.

> + */
> +static size_t
> +pci_vpd_pci22_size(struct pci_dev *dev)
> +{
> +       size_t off = 0;
> +       unsigned char header[1+2];      /* 1 byte tag, 2 bytes length */
> +
> +       while (off < PCI_VPD_PCI22_SIZE &&
> +              pci_read_vpd(dev, off, 1, header) == 1) {
> +               unsigned char tag;
> +

The offset comparison is probably redundant.  There is already a check
in pci_vpd_pci22_read that will check the offset and return -EINVAL if
we have exceeded vpd->base.len.  As such you can probably just do the
pci_read_vpd comparison and drop the offset length entirely.

> +               if (header[0] & PCI_VPD_LRDT) {
> +                       /* Large Resource Data Type Tag */
> +                       tag = pci_vpd_lrdt_tag(header);
> +                       /* Only read length from known tag items */
> +                       if ((tag == PCI_VPD_LTIN_ID_STRING) ||
> +                           (tag == PCI_VPD_LTIN_RO_DATA) ||
> +                           (tag == PCI_VPD_LTIN_RW_DATA)) {
> +                               if (pci_read_vpd(dev, off+1, 2,
> +                                                &header[1]) != 2)
> +                                       return off + 1;
> +                               off += PCI_VPD_LRDT_TAG_SIZE +
> +                                       pci_vpd_lrdt_size(header);
> +                       }
> +               } else {
> +                       /* Short Resource Data Type Tag */
> +                       off += PCI_VPD_SRDT_TAG_SIZE +
> +                               pci_vpd_srdt_size(header);
> +                       tag = pci_vpd_srdt_tag(header);
> +               }
> +               if (tag == PCI_VPD_STIN_END)    /* End tag descriptor */
> +                       return off;
> +               if ((tag != PCI_VPD_LTIN_ID_STRING) &&
> +                   (tag != PCI_VPD_LTIN_RO_DATA) &&
> +                   (tag != PCI_VPD_LTIN_RW_DATA)) {
> +                       dev_dbg(&dev->dev,
> +                               "invalid %s vpd tag %02x at offset %zu.",
> +                               (header[0] & PCI_VPD_LRDT) ? "large" : "short",
> +                               tag, off);
> +                       break;
> +               }
> +       }
> +       return 0;
> +}
> +
>  int pci_vpd_pci22_init(struct pci_dev *dev)
>  {
>         struct pci_vpd_pci22 *vpd;
> @@ -497,6 +547,13 @@ int pci_vpd_pci22_init(struct pci_dev *dev)
>         vpd->cap = cap;
>         vpd->busy = false;
>         dev->vpd = &vpd->base;
> +       vpd->base.len = pci_vpd_pci22_size(dev);
> +       if (vpd->base.len == 0) {
> +               dev_dbg(&dev->dev, "Disabling VPD access.");
> +               dev->vpd = NULL;
> +               kfree(vpd);
> +               return -ENXIO;
> +       }
>         return 0;
>  }

It looks like this still doesn't address the VPD_REF_F0 issue I
mentioned earlier.  We don't need to compute the length for each
function we only need to do it once.  I would recommend modifying
things so that you set vpd->base.len to 0 if the VPD_REF_F0 flag is
set.

Also I wouldn't delete the vpd configuration if the length is not
correct as that will likely break several quirks that already exist
that are setting the length.  Also there is no need to return an
error, the fact is the part has VPD but we cannot determine the length
as such the correct solution is to leave it at 0.  We can leave that
for a quirk to sort out later if needed.  You could probably move the
dev_dbg message to just before the return 0 in the pci_vpd_pci22_size
call and drop the entire if statement in the init function.

- Alex
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