[dpdk-stable] [PATCH v4] bus/pci: fix VF bus error for memory access

[David Marchand]

On Thu, Jun 25, 2020 at 6:00 AM Haiyue Wang <haiyue.wang at intel.com> 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 bus memory space through PCI read/write access. According to
> the PCIe specification, the 'Memory Space Enable' is always zero for VF:
>
>              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.    |            |
> -------------+--------------------------------+------------+-----------
>
> Afterwards the vfio-pci will initialize its own virtual PCI config space
> data ('vconfig') by reading the VF's physical PCI config space, then the
> 'Memory Space Enable' bit in vconfig will always be 0b value. This will
> make the vfio-pci treat the BAR memory space as disabled, and the SIGBUS
> will be triggered if access these BARs.
>
> By investigation, the VF PCI device *passthrough* into the Guest OS by
> QEMU has the 'Memory Space Enable' with 1b value. That's because every
> PCI driver will start to enable the memory space, and this action will
> be hooked by vfio-pci virtual PCI read/write to set the 'Memory Space
> Enable' in vconfig space to 1b. So VF runs in guest OS has 'Mem+', but
> VF runs in host OS has 'Mem-'.
>
> Align with PCI working mode in Guest/QEMU/Host, in DPDK, enable the PCI
> bus memory space explicitly to avoid access on disabled memory.
>
> Fixes: 33604c31354a ("vfio: refactor PCI BAR mapping")
> Cc: stable at dpdk.org
>
> Signed-off-by: Haiyue Wang <haiyue.wang at intel.com>
> Acked-by: Anatoly Burakov <anatoly.burakov at intel.com>
> Tested-by: Harman Kalra <hkalra at marvell.com>
> Tested-by: David Marchand <david.marchand at redhat.com>
Tested-by: Thierry Martin <thierry.martin.public at gmail.com>

Applied, thanks again Haiyue.


Kevin, Luca,

I can see that some distros have already started backporting the fix
in kernel (fc31, fc32 and rhel7 at least for what I saw).
18.11 and 19.11 will need this fix at some point.
I'll let you decide on the proper timing.


-- 
David Marchand