From 0dff1b407def32452a0d80148172889862c64fe7 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Thu, 16 Nov 2023 15:15:45 -0500 Subject: mm/pagemap: fix ioctl(PAGEMAP_SCAN) on vma check Patch series "mm/pagemap: A few fixes to the recent PAGEMAP_SCAN". This series should fix two known reports from syzbot on the new PAGEMAP_SCAN ioctl(): https://lore.kernel.org/all/000000000000b0e576060a30ee3b@google.com/ https://lore.kernel.org/all/000000000000773fa7060a31e2cc@google.com/ The 3rd patch is something I found when testing these patches. This patch (of 3): The new ioctl(PAGEMAP_SCAN) relies on vma wr-protect capability provided by userfault, however in the vma test it didn't explicitly require the vma to have wr-protect function enabled, even if PM_SCAN_WP_MATCHING flag is set. It means the pagemap code can now apply uffd-wp bit to a page in the vma even if not registered to userfaultfd at all. Then in whatever way as long as the pte got written and page fault resolved, we'll apply the write bit even if uffd-wp bit is set. We'll see a pte that has both UFFD_WP and WRITE bit set. Anything later that looks up the pte for uffd-wp bit will trigger the warning: WARNING: CPU: 1 PID: 5071 at arch/x86/include/asm/pgtable.h:403 pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline] Fix it by doing proper check over the vma attributes when PM_SCAN_WP_MATCHING is specified. Link: https://lkml.kernel.org/r/20231116201547.536857-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20231116201547.536857-2-peterx@redhat.com Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") Signed-off-by: Peter Xu Reported-by: syzbot+e94c5aaf7890901ebf9b@syzkaller.appspotmail.com Reviewed-by: David Hildenbrand Reviewed-by: Andrei Vagin Reviewed-by: Muhammad Usama Anjum Signed-off-by: Andrew Morton --- fs/proc/task_mmu.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index ef2eb12906da..a6f88cbfb689 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1982,15 +1982,31 @@ static int pagemap_scan_test_walk(unsigned long start, unsigned long end, struct pagemap_scan_private *p = walk->private; struct vm_area_struct *vma = walk->vma; unsigned long vma_category = 0; + bool wp_allowed = userfaultfd_wp_async(vma) && + userfaultfd_wp_use_markers(vma); - if (userfaultfd_wp_async(vma) && userfaultfd_wp_use_markers(vma)) - vma_category |= PAGE_IS_WPALLOWED; - else if (p->arg.flags & PM_SCAN_CHECK_WPASYNC) - return -EPERM; + if (!wp_allowed) { + /* User requested explicit failure over wp-async capability */ + if (p->arg.flags & PM_SCAN_CHECK_WPASYNC) + return -EPERM; + /* + * User requires wr-protect, and allows silently skipping + * unsupported vmas. + */ + if (p->arg.flags & PM_SCAN_WP_MATCHING) + return 1; + /* + * Then the request doesn't involve wr-protects at all, + * fall through to the rest checks, and allow vma walk. + */ + } if (vma->vm_flags & VM_PFNMAP) return 1; + if (wp_allowed) + vma_category |= PAGE_IS_WPALLOWED; + if (!pagemap_scan_is_interesting_vma(vma_category, p)) return 1; -- cgit v1.2.3