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