Re: [dpdk-stable] [PATCH v2] bus/pci: fix VF bus error for memory access

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 22-Jun-20 7:30 AM, Haiyue Wang wrote:
> To fix CVE-2020-12888, the linux vfio-pci module will invalidate mmaps
> and block MMIO access on disabled memory, it will send a SIGBUS to the
> application:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=abafbc551fddede3e0a08dee1dcde08fc0eb8476
> 
> When the application opens the vfio PCI device, the vfio-pci module will
> enable the memory bus command through PCI read/write access. According
> to the PCIe specification, for VF, the 'Memory Space Enable' is always
> zero:
> 
>               Table 9-13 Command Register Changes
> 
> Bit Location | PF and VF Register Differences | PF         | VF
>               | From Base                      | Attributes | Attributes
> -------------+--------------------------------+------------+-----------
>               | Memory Space Enable - Does not |            |
>               | apply to VFs. Must be hardwired|  Base      |  0b
>       1       | to 0b for VFs. VF Memory Space |            |
>               | is controlled by the VF MSE bit|            |
>               | in the VF Control register.    |            |
> -------------+--------------------------------+------------+-----------
> 
> Then the vfio-pci module initializes its own virtual PCI config space
> data ('vconfig') by reading the VF's physical PCI config space, so the
> 'Memory Space Enable' bit in vconfig will also have 0b value. This will
> make the vfio-pci find that the BAR memory is disabled, and the SIGBUS
> will be triggerred if access these BARs.
> 
> So it needs to enable PCI bus memory command explicitly to avoid access
> on disabled memory, which will call vfio-pci virtual PCI read/write API
> to set the 'Memory Space Enable' in vconfig space to 1b.
> 
> Fixes: 33604c31354a ("vfio: refactor PCI BAR mapping")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>

The patch itself looks good, but i wonder how far back do these go, and 
do we need workarounds for older kernels. IIRC v17.11 is still a 
supported release, and its kernel support might go back all the way to 
v3.6 when VFIO was first introduced.

> ---
> v2: Rewrite the commit log, and put the link into it even it is long.
> ---
>   drivers/bus/pci/linux/pci_vfio.c | 37 ++++++++++++++++++++++++++++++++
>   1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/bus/pci/linux/pci_vfio.c b/drivers/bus/pci/linux/pci_vfio.c
> index 64cd84a68..9b6e45da5 100644
> --- a/drivers/bus/pci/linux/pci_vfio.c
> +++ b/drivers/bus/pci/linux/pci_vfio.c
> @@ -149,6 +149,38 @@ pci_vfio_get_msix_bar(int fd, struct pci_msix_table *msix_table)
>   	return 0;
>   }
>   
> +/* enable PCI bus memory command */
> +static int
> +pci_vfio_enable_bus_memory(int dev_fd)
> +{
> +	uint16_t cmd;
> +	int ret;
> +
> +	ret = pread64(dev_fd, &cmd, sizeof(cmd),
> +		      VFIO_GET_REGION_ADDR(VFIO_PCI_CONFIG_REGION_INDEX) +
> +		      PCI_COMMAND);
> +
> +	if (ret != sizeof(cmd)) {
> +		RTE_LOG(ERR, EAL, "Cannot read command from PCI config space!\n");
> +		return -1;
> +	}
> +
> +	if (cmd & PCI_COMMAND_MEMORY)
> +		return 0;
> +
> +	cmd |= PCI_COMMAND_MEMORY;
> +	ret = pwrite64(dev_fd, &cmd, sizeof(cmd),
> +		       VFIO_GET_REGION_ADDR(VFIO_PCI_CONFIG_REGION_INDEX) +
> +		       PCI_COMMAND);
> +
> +	if (ret != sizeof(cmd)) {
> +		RTE_LOG(ERR, EAL, "Cannot write command to PCI config space!\n");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
>   /* set PCI bus mastering */
>   static int
>   pci_vfio_set_bus_master(int dev_fd, bool op)
> @@ -427,6 +459,11 @@ pci_rte_vfio_setup_device(struct rte_pci_device *dev, int vfio_dev_fd)
>   		return -1;
>   	}
>   
> +	if (pci_vfio_enable_bus_memory(vfio_dev_fd)) {
> +		RTE_LOG(ERR, EAL, "Cannot enable bus memory command!\n");

Nitpick, but i think the word "command" is unneeded here :)

> +		return -1;
> +	}
> +
>   	/* set bus mastering for the device */
>   	if (pci_vfio_set_bus_master(vfio_dev_fd, true)) {
>   		RTE_LOG(ERR, EAL, "Cannot set up bus mastering!\n");
> 


-- 
Thanks,
Anatoly