On Fri, 19 Mar 2021 22:24:28 +0700 Bui Quang Minh <minhquangbui99@xxxxxxxxx> wrote: > userfaultfd_writeprotect() use change_protection() to clear write bit in > page table entries (pte/pmd). So, later write to this virtual address > range causes a page fault, which is then handled by userspace program. > However, change_protection() has no effect when there is no page table > entries associated with that virtual memory range (a newly mapped memory > range). As a result, later access to that memory range causes allocating a > page table entry with write bit still set (due to VM_WRITE flag in > vma->vm_flags). > > Add checks for VM_UFFD_WP in vma->vm_flags when allocating new page table > entry in missing page table entry page fault path. This sounds like a pretty significant bug? Would it be possible to add a test to tools/testing/selftests/vm/userfaultfd.c to check for this? It should fail without your patch and succeed with it. Thanks.
