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,