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. -- David Marchand
