On Wed, Jan 15, 2025 at 04:58:06PM +0000, Ryan Roberts wrote: > Hi Peter, David, Hey, Ryan, > > On 07/01/2025 14:47, Ryan Roberts wrote: > > When mremap()ing a memory region previously registered with userfaultfd > > as write-protected but without UFFD_FEATURE_EVENT_REMAP, an > > inconsistency in flag clearing leads to a mismatch between the vma flags > > (which have uffd-wp cleared) and the pte/pmd flags (which do not have > > uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) > > to trigger a warning in page_table_check_pte_flags() due to setting the > > pte to writable while uffd-wp is still set. > > > > Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any > > such mremap() so that the values are consistent with the existing > > clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless > > of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover > > PTE, huge PMD and hugetlb paths. > > I just noticed that Andrew sent this to Linus and it's now in his tree; I'm > suddenly very nervous that it doesn't have any acks. I don't suppose you would > be able to do a quick review to calm the nerves?? Heh, I fully trusted you, and I appreciated your help too. I'll need to run for 1-2 hours, but I'll read it this afternoon. Side note: no review is as good as tests on reliability POV if that was the concern, but I'll try my best. Thanks, -- Peter Xu
