| Message ID | 1363332390-12754-4-git-send-email-shangw@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 2013-03-15 at 15:26 +0800, Gavin Shan wrote: > The config registers in [0, 0x40] is being supported by VFIO. Apart > from that, the other config registers should be coverred by PCI or > PCIe capability. However, there might have some PCI devices (be2net) > who has config registers (0x7c) out of [0, 0x40], and don't have > corresponding PCI or PCIe capability. VFIO will return 0x0 on reading > those registers and writing is dropped. It caused the be2net driver > fails to be loaded because 0x0 returned from its config register 0x7c. > > The patch changes the behaviour so that those config registers out > of [0, 0x40] and don't have corresponding PCI or PCIe capability > will be accessed directly. This basically gives userspace free access to any regions that aren't covered by known capabilities. We have no idea what this might expose on some devices. I'd like to support be2net, but what's the minimal access that it needs? Can we provide 2 or 4 bytes of read-only access at offset 0x7c for just that device? Is it always 0x7c? Let's split this patch from the series since it's clearly dealing with something independent. Thanks, Alex > Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com> > --- > drivers/vfio/pci/vfio_pci_config.c | 31 ++++++++++++++++++++----------- > 1 files changed, 20 insertions(+), 11 deletions(-) > > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c > index 964ff22..5ea3afb 100644 > --- a/drivers/vfio/pci/vfio_pci_config.c > +++ b/drivers/vfio/pci/vfio_pci_config.c > @@ -1471,18 +1471,27 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_device *vdev, char __user *buf, > > cap_id = vdev->pci_config_map[*ppos / 4]; > > + /* > + * Some PCI device config registers might not be coverred by > + * capability and useful. We will enable direct access to > + * those registers. > + */ > if (cap_id == PCI_CAP_ID_INVALID) { > - if (iswrite) > - return ret; /* drop */ > - > - /* > - * Per PCI spec 3.0, section 6.1, reads from reserved and > - * unimplemented registers return 0 > - */ > - if (copy_to_user(buf, &val, count)) > - return -EFAULT; > - > - return ret; > + if (iswrite) { > + if (copy_from_user(&val, buf, count)) > + return -EFAULT; > + ret = vfio_user_config_write(vdev->pdev, (int)(*ppos), > + val, count); > + return ret ? ret : count; > + } else { > + ret = vfio_user_config_read(vdev->pdev, (int)(*ppos), > + &val, count); > + if (ret) > + return ret; > + if (copy_to_user(buf, &val, count)) > + return -EFAULT; > + return count; > + } > } > > /* -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2013-03-15 at 13:41 -0600, Alex Williamson wrote: > > This basically gives userspace free access to any regions that aren't > covered by known capabilities. And ? I mean seriously :-) We already had that discussion ... trying to "protect" config space is just plain doomed. There is no point. It makes sense to do things like emulate BARs etc... for things to function properly under some circumstances/setups where you can't just expose the original BAR values to the guest and have the HW take care of it but you *must* be prepared to deal with anything in config space being changed without you knowing about it. Devices *will* have backdoors via MMIO. Period. You cannot rely on those not existing, whether they are documented or not. If you can't cope with the config space accesses then you aren't properly isolated. It can be deemed acceptable (depends what you use your VMs for) but that I mean is that any config space filtering/emulation for the sake of "security" is ... pointless. Doing it for functionality to work at all (ie BAR emulation) is fine, but that's about it. IE. As a mean of security it's pointless. > We have no idea what this might expose on some devices. No more than we have any idea what MMIO mapping of the device register space exposes :-) > I'd like to support be2net, but what's the minimal > access that it needs? Can we provide 2 or 4 bytes of read-only access > at offset 0x7c for just that device? Is it always 0x7c? Let's split > this patch from the series since it's clearly dealing with something > independent. Thanks, Ben. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat, 2013-03-16 at 06:30 +0100, Benjamin Herrenschmidt wrote: > On Fri, 2013-03-15 at 13:41 -0600, Alex Williamson wrote: > > > > This basically gives userspace free access to any regions that aren't > > covered by known capabilities. > > And ? > > I mean seriously :-) We already had that discussion ... trying to > "protect" config space is just plain doomed. There is no point. > > It makes sense to do things like emulate BARs etc... for things to > function properly under some circumstances/setups where you can't just > expose the original BAR values to the guest and have the HW take care of > it but you *must* be prepared to deal with anything in config space > being changed without you knowing about it. > > Devices *will* have backdoors via MMIO. Period. You cannot rely on those > not existing, whether they are documented or not. > > If you can't cope with the config space accesses then you aren't > properly isolated. It can be deemed acceptable (depends what you use > your VMs for) but that I mean is that any config space > filtering/emulation for the sake of "security" is ... pointless. > > Doing it for functionality to work at all (ie BAR emulation) is fine, > but that's about it. IE. As a mean of security it's pointless. > > > > We have no idea what this might expose on some devices. > > No more than we have any idea what MMIO mapping of the device register > space exposes :-) Yeah, yeah. Ok, I can't come up with a reasonable argument otherwise, it'll give us better device support, and I believe pci-assign has always done this. I'll take another look at the patch. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2013-03-15 at 15:26 +0800, Gavin Shan wrote: > The config registers in [0, 0x40] is being supported by VFIO. Apart > from that, the other config registers should be coverred by PCI or > PCIe capability. However, there might have some PCI devices (be2net) > who has config registers (0x7c) out of [0, 0x40], and don't have > corresponding PCI or PCIe capability. VFIO will return 0x0 on reading > those registers and writing is dropped. It caused the be2net driver > fails to be loaded because 0x0 returned from its config register 0x7c. > > The patch changes the behaviour so that those config registers out > of [0, 0x40] and don't have corresponding PCI or PCIe capability > will be accessed directly. > > Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com> > --- Hi Gavin, I'm onboard with making this change now, but this patch isn't sufficient. The config space map uses a byte per dword to index the capability since both standard and extended capabilities are dword aligned. We currently have a bug that this patch exposes that we round the length down, ex. a 14 byte MSI capability becomes 12 bytes leaving the message data now exposed and writable with this patch. That bug can be fixed by aligning the length so the capability fills the dword, but notice that 0x7c on the be2net is filling one of these gaps. So fixing that bug attaches that gap to the previous capability instead of allowing direct access. So, before we can make this change we need to fix the config map to have byte granularity. Thanks, Alex > drivers/vfio/pci/vfio_pci_config.c | 31 ++++++++++++++++++++----------- > 1 files changed, 20 insertions(+), 11 deletions(-) > > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c > index 964ff22..5ea3afb 100644 > --- a/drivers/vfio/pci/vfio_pci_config.c > +++ b/drivers/vfio/pci/vfio_pci_config.c > @@ -1471,18 +1471,27 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_device *vdev, char __user *buf, > > cap_id = vdev->pci_config_map[*ppos / 4]; > > + /* > + * Some PCI device config registers might not be coverred by > + * capability and useful. We will enable direct access to > + * those registers. > + */ > if (cap_id == PCI_CAP_ID_INVALID) { > - if (iswrite) > - return ret; /* drop */ > - > - /* > - * Per PCI spec 3.0, section 6.1, reads from reserved and > - * unimplemented registers return 0 > - */ > - if (copy_to_user(buf, &val, count)) > - return -EFAULT; > - > - return ret; > + if (iswrite) { > + if (copy_from_user(&val, buf, count)) > + return -EFAULT; > + ret = vfio_user_config_write(vdev->pdev, (int)(*ppos), > + val, count); > + return ret ? ret : count; > + } else { > + ret = vfio_user_config_read(vdev->pdev, (int)(*ppos), > + &val, count); > + if (ret) > + return ret; > + if (copy_to_user(buf, &val, count)) > + return -EFAULT; > + return count; > + } > } > > /* -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c index 964ff22..5ea3afb 100644 --- a/drivers/vfio/pci/vfio_pci_config.c +++ b/drivers/vfio/pci/vfio_pci_config.c @@ -1471,18 +1471,27 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_device *vdev, char __user *buf, cap_id = vdev->pci_config_map[*ppos / 4]; + /* + * Some PCI device config registers might not be coverred by + * capability and useful. We will enable direct access to + * those registers. + */ if (cap_id == PCI_CAP_ID_INVALID) { - if (iswrite) - return ret; /* drop */ - - /* - * Per PCI spec 3.0, section 6.1, reads from reserved and - * unimplemented registers return 0 - */ - if (copy_to_user(buf, &val, count)) - return -EFAULT; - - return ret; + if (iswrite) { + if (copy_from_user(&val, buf, count)) + return -EFAULT; + ret = vfio_user_config_write(vdev->pdev, (int)(*ppos), + val, count); + return ret ? ret : count; + } else { + ret = vfio_user_config_read(vdev->pdev, (int)(*ppos), + &val, count); + if (ret) + return ret; + if (copy_to_user(buf, &val, count)) + return -EFAULT; + return count; + } } /*
The config registers in [0, 0x40] is being supported by VFIO. Apart from that, the other config registers should be coverred by PCI or PCIe capability. However, there might have some PCI devices (be2net) who has config registers (0x7c) out of [0, 0x40], and don't have corresponding PCI or PCIe capability. VFIO will return 0x0 on reading those registers and writing is dropped. It caused the be2net driver fails to be loaded because 0x0 returned from its config register 0x7c. The patch changes the behaviour so that those config registers out of [0, 0x40] and don't have corresponding PCI or PCIe capability will be accessed directly. Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com> --- drivers/vfio/pci/vfio_pci_config.c | 31 ++++++++++++++++++++----------- 1 files changed, 20 insertions(+), 11 deletions(-)