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

[Kevin Traynor <ktraynor@redhat.com>]

On 25/06/2020 19:33, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: Kevin Traynor <ktraynor@redhat.com>
>> Sent: Friday, June 26, 2020 00:46
>> To: David Marchand <david.marchand@redhat.com>; Wang, Haiyue <haiyue.wang@intel.com>; Luca Boccassi
>> <bluca@debian.org>
>> Cc: dev <dev@dpdk.org>; Burakov, Anatoly <anatoly.burakov@intel.com>; dpdk stable <stable@dpdk.org>;
>> Harman Kalra <hkalra@marvell.com>
>> Subject: Re: [PATCH v4] bus/pci: fix VF bus error for memory access
>>
>> 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=abafbc551fddede3e0a08dee
>> 1dcde08fc0eb8476
>>>>
>>>> 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.
> 
> Alex post a fix in kernel just now. So looks like the DPDK patch is nice
> to have, not a MUST. ;-)
> 

Thanks for the update Haiyue. That may be true in the future, but not at
the moment. The patch is just submitted yesterday, so I don't know how
long it will take to filter through to all the distro kernels (and users
to update).

I think it's still worth to take this patch now in 18.11. I will wait
until this afternoon in case anyone has reasons not to.

thanks,
Kevin.

> https://lore.kernel.org/kvm/159310421505.27590.16617666489295503039.stgit@gimli.home/T/#u
>