On Fri, 29 Apr 2016 18:55:14 +1000
Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:
> PCI-Express spec says that reading 4 bytes at offset 100h should return
> zero if there is no extended capability so VFIO reads this dword to
> know if there are extended capabilities.
>
> However it is not always possible to access the extended space so
> generic PCI code in pci_cfg_space_size_ext() checks if
> pci_read_config_dword() can read beyond 100h and if the check fails,
> it sets the config space size to 100h.
>
> VFIO does its own extended capabilities check by reading at offset 100h
> which may produce 0xffffffff which VFIO treats as the extended config
> space presense and calls vfio_ecap_init() which fails to parse
> capabilities (which is expected) but right before the exit, it writes
> zero at offset 100h which is beyond the buffer allocated for
> vdev->vconfig (which is 256 bytes) which leads to random memory
> corruption.
>
> This makes VFIO only check for the extended capabilities if
> the discovered config size is more than 256 bytes.
>
> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> ---
> Changes:
> v2:
> * instead of checking for 0xffffffff, this only does the check if
> device's config size is big enough
> ---
I'll take this patch separately, please drop from this series. Thanks,
Alex
> drivers/vfio/pci/vfio_pci_config.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 142c533..d0c4358 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1124,9 +1124,12 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
> return pcibios_err_to_errno(ret);
>
> if (PCI_X_CMD_VERSION(word)) {
> - /* Test for extended capabilities */
> - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> - vdev->extended_caps = (dword != 0);
> + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> + /* Test for extended capabilities */
> + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE,
> + &dword);
> + vdev->extended_caps = (dword != 0);
> + }
> return PCI_CAP_PCIX_SIZEOF_V2;
> } else
> return PCI_CAP_PCIX_SIZEOF_V0;
> @@ -1138,9 +1141,11 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
>
> return byte;
> case PCI_CAP_ID_EXP:
> - /* Test for extended capabilities */
> - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> - vdev->extended_caps = (dword != 0);
> + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> + /* Test for extended capabilities */
> + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> + vdev->extended_caps = dword != 0;
> + }
>
> /* length based on version */
> if ((pcie_caps_reg(pdev) & PCI_EXP_FLAGS_VERS) == 1)
--
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