On Fri, Nov 09, 2018 at 06:16:37PM -0500, Venkatesh Srinivas wrote:
> Userspace code using uio_pci_generic may enable bus-mastering by
> directly manipulating a PCI device's command register. If a userspace
> program enables bus-mastering but exits/crashes uncleanly, bus-
> mastering will still be enabled and stale DMA addresses may be
> programmed and live in the device.
>
> Disable bus-mastering unconditionally on last close of a UIO PCI fd
> to avoid this. If the device did not have bus-mastering enabled,
> pci_clear_master() is a no-op.
>
> Signed-off-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxx>
> Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Reviewed-by: Catherine Sullivan <csully@xxxxxxxxxx>
> ---
> drivers/uio/uio_pci_generic.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
> index 8773e373ffe5..832af15678ef 100644
> --- a/drivers/uio/uio_pci_generic.c
> +++ b/drivers/uio/uio_pci_generic.c
> @@ -39,6 +39,14 @@ to_uio_pci_generic_dev(struct uio_info *info)
> return container_of(info, struct uio_pci_generic_dev, info);
> }
>
> +static int release(struct uio_info *info, struct inode *inode)
> +{
> + struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
An empty line would add readability here.
> + /* Stop the device from initiating further DMAs */
UIO is intended for non-DMA capable devices, since
it doesn't enforce IOMMU protection.
So this "further DMA" worries me as it might make people think it's ok.
How about:
/* This driver is insecure when used with devices doing DMA,
* but some people (mis)use it with such devices.
* Let's at least make sure DMA isn't left enabled
* after the userspace driver closes the fd.
* Note that there's a non-zero chance doing this will wedge the device
* at least until reset.
*/
> + pci_clear_master(gdev->pdev);
> + return 0;
> +}
> +
> /* Interrupt handler. Read/modify/write the command register to disable
> * the interrupt. */
> static irqreturn_t irqhandler(int irq, struct uio_info *info)
> @@ -78,6 +86,7 @@ static int probe(struct pci_dev *pdev,
>
> gdev->info.name = "uio_pci_generic";
> gdev->info.version = DRIVER_VERSION;
> + gdev->info.release = release;
> gdev->pdev = pdev;
> if (pdev->irq) {
> gdev->info.irq = pdev->irq;
> --
> 2.19.1.930.g4563a0d9d0-goog
