On Tue, 14 Apr 2020 23:47:40 +0000 "Tian, Kevin" <[email protected]> wrote:
> > From: Jacob Pan <[email protected]> > > Sent: Wednesday, April 15, 2020 6:32 AM > > > > On Tue, 14 Apr 2020 10:13:04 -0700 > > Jacob Pan <[email protected]> wrote: > > > > > > > > In any of the proposed solutions, the > > > > > > IOMMU driver is ultimately responsible for validating the > > > > > > user data, so do we want vfio performing the > > > > > > copy_from_user() to an object that could later be assumed > > > > > > to be sanitized, or should vfio just pass a user pointer to > > > > > > make it obvious that the consumer is responsible for all > > > > > > the user protections? Seems like the latter. > > > > > I like the latter as well. > > > > > > > On a second thought, I think the former is better. Two reasons: > > > > 1. IOMMU API such as page_response is also used in baremetal. So it > > is not suitable to pass a __user *. > > https://www.spinics.net/lists/arm-kernel/msg798677.html > > You can have a wrapped version accepting a __user* and an internal > version for kernel pointers. > I have thought about that also but the problem is that some of the flags are processed in the vendor IOMMU ops so it is hard to do that in a generic wrapper. > > > > 2. Some data are in the mandatory (fixed offset, never removed or > > extended) portion of the uAPI structure. It is simpler for VFIO to > > extract that and pass it to IOMMU API. For example, the PASID value > > used for unbind_gpasid(). VFIO also need to sanitize the PASID > > value to make sure it belongs to the same VM that did the > > allocation. > > I don't think this makes much difference. If anyway you still plan to > let IOMMU driver parse some user pointers, why not making a clear > split to have it sparse all IOMMU specific fields? > The plan is not to have IOMMU driver parse user pointers. This is the "former" case in Alex's comment. I.e. vfio performing the copy_from_user based on argsz in IOMMU uAPI. > Thanks > Kevin > > > > > > > > > > > That still really > > > > > > doesn't address what's in that user data blob yet, but the > > > > > > vfio interface could be: > > > > > > > > > > > > struct { > > > > > > __u32 argsz; > > > > > > __u32 flags; > > > > > > __u8 data[]; > > > > > > } > > > > > > > > > > > > Where flags might be partitioned like we do for > > > > > > DEVICE_FEATURE to indicate the format of data and what vfio > > > > > > should do with it, and data might simply be defined as a > > > > > > (__u64 __user *). > > > > > So, __user * will be passed to IOMMU driver if VFIO checks > > > > > minsz include flags and they are valid. > > > > > IOMMU driver can copy the rest based on the mandatory > > > > > version/minsz and flags in the IOMMU uAPI structs. > > > > > Does it sound right? This is really choice #2. > > > > > > > > Sounds like each IOMMU UAPI struct just needs to have an > > > > embedded size and flags field, but yes. > > > > > > > Yes, an argsz field can be added to each UAPI. There are already > > > flags or the equivalent. IOMMU driver can process the __user * > > > based on the argsz, flags, check argsz against > > > offsetofend(iommu_uapi_struct, last_element), etc.; [Jacob Pan] _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
