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

[Kevin Traynor <ktraynor@redhat.com>]

On 25/06/2020 15:09, David Marchand wrote:
> On Thu, Jun 25, 2020 at 6:00 AM Haiyue Wang <haiyue.wang@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@dpdk.org
>>
>> Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
>> Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
>> Tested-by: Harman Kalra <hkalra@marvell.com>
>> Tested-by: David Marchand <david.marchand@redhat.com>
> Tested-by: Thierry Martin <thierry.martin.public@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.
> 
> 

It looks an important fix. I think it's worth having in 18.11.9. I will
apply and create an 18.11.9-rc2 tomorrow, so if anyone hasn't started
validation already, they can validate with it in.