On Wed, Apr 23, 2025 at 08:13:33PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 23, 2025 at 11:31:29AM -0700, Nicolin Chen wrote: > > > > It also needs to act like a mdev and lock down the part of the IOAS > > > that provides that memory so the pin can't be released and UAF things. > > > > If I capture this correctly, the GPA->PA mapping is already done > > at the IOAS level for the S2 HWPT/domain, i.e. pages are already > > pinned. So we just need to a pair of for-driver APIs to validate > > the contiguity and refcount pages calling iopt_area_add_access(). > > Yes, adding an access is the key thing, the access will give you a > page list which you can validate, but it also provides a way to > synchronize if a hostile userspace does an unmap.
The new APIs are very like iommufd_access_pin/unpin_pages(). But to reduce the amount of code that we have to share with driver.o, I added a smaller iopt_area_get/put_access() that gets an access and increases/decreases the refcounts only. Yet, this still inevitably doubled (-ish) the size of driver.o: text data bss dec hex filename 4429 296 0 4725 1275 drivers/iommu/iommufd/driver.o text data bss dec hex filename 8430 783 0 9213 23fd drivers/iommu/iommufd/driver.o Meanwhile, I am thinking if we could use the known S2 domain to translate the GPAs to PAs for the contiguity test, which feels a little cleaner to do in an IOMMU driver v.s. with a page list? Thanks Nicolin
