On Tue, Oct 06, 2015 at 12:43:45AM +0300, Vladislav Zolotarov wrote: > So, like it has already been asked in a different thread I'm going to > ask a rhetorical question: what adding an MSI and MSI-X interrupts support to > uio_pci_generic has to do with security?
memory protection is a better term than security. It's very simple: you enable bus mastering and you ask userspace to map all device BARs. One of these BARs holds the address to which device writes to trigger MSI-X interrupt. This is how MSI-X works, internally: from the point of view of PCI it's a memory write. It just so happens that the destination address is in the interrupt controller, that triggers an interrupt. But a bug in this userspace application can corrupt the MSI-X table, which in turn can easily corrupt kernel memory, or unrelated processes's memory. This is in my opinion unacceptable. So you need to be very careful - probably need to reset device before you even enable bus master - prevent userspace from touching msi config - prevent userspace from moving BARs since msi-x config is within a BAR - detect reset and prevent linux from touching device while it's under reset The list goes on and on. This is pretty much what VFIO spent the last 3 years doing, except VFIO also can do IOMMU groups. > What "security threat" does it add > that u don't already have today? Yes, userspace can create this today if it tweaks PCI config space to enable MSI-X, then corrupts the MSI-X table. It's unfortunate that we don't yet prevent this, but at least you need two things to go wrong for this to trigger. The reason, as I tried to point out, is simply that I didn't think uio_pci_generic will be used for these configurations. But there's nothing fundamental here that makes them secure and that therefore makes your patches secure as well. Fixing this to make uio_pci_generic write-protect MSI/MSI-X enable registers sounds kind of reasonable, this shouldn't be too hard. -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
