Messages in this thread Patch in this message | | | Date | Thu, 16 Nov 2023 10:19:13 +0100 | Subject | Re: [syzbot] [mm?] WARNING in unmap_page_range (2) | From | David Hildenbrand <> |
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On 15.11.23 23:00, Andrew Morton wrote: > On Wed, 15 Nov 2023 05:32:19 -0800 syzbot <syzbot+7ca4b2719dc742b8d0a4@syzkaller.appspotmail.com> wrote: > >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: ac347a0655db Merge tag 'arm64-fixes' of git://git.kernel.o.. >> git tree: upstream >> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15ff3057680000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=287570229f5c0a7c >> dashboard link: https://syzkaller.appspot.com/bug?extid=7ca4b2719dc742b8d0a4 >> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=162a25ff680000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13d62338e80000 >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/00e30e1a5133/disk-ac347a06.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/07c43bc37935/vmlinux-ac347a06.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/c6690c715398/bzImage-ac347a06.xz >> >> The issue was bisected to: >> >> commit 12f6b01a0bcbeeab8cc9305673314adb3adf80f7 >> Author: Muhammad Usama Anjum <usama.anjum@collabora.com> >> Date: Mon Aug 21 14:15:15 2023 +0000 >> >> fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag > > Thanks. The bisection is surprising, but the mentioned patch does > mess with pagemap. > > How about we add this? > > From: Andrew Morton <akpm@linux-foundation.org> > Subject: mm/memory.c:zap_pte_range() print bad swap entry > Date: Wed Nov 15 01:54:18 PM PST 2023 > > We have a report of this WARN() triggering. Let's print the offending > swp_entry_t to help diagnosis. > > Link: https://lkml.kernel.org/r/000000000000b0e576060a30ee3b@google.com > Cc: Muhammad Usama Anjum <usama.anjum@collabora.com> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > mm/memory.c | 1 + > 1 file changed, 1 insertion(+) > > --- a/mm/memory.c~a > +++ a/mm/memory.c > @@ -1521,6 +1521,7 @@ static unsigned long zap_pte_range(struc > continue; > } else { > /* We should have covered all the swap entry types */ > + pr_alert("unrecognized swap entry 0x%lx\n", entry.val); > WARN_ON_ONCE(1); > } > pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); > _ >
I'm curious if
1) make_uffd_wp_pte() won't end up overwriting existing pte markers, for example, if PTE_MARKER_POISONED is set. [unrelated to this bug]
2) We get the error on arm64, which does *not* support uffd-wp. Do we maybe end up calling make_uffd_wp_pte() and place a pte marker, even though we don't have CONFIG_PTE_MARKER_UFFD_WP?
static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry) { #ifdef CONFIG_PTE_MARKER_UFFD_WP return is_pte_marker_entry(entry) && (pte_marker_get(entry) & PTE_MARKER_UFFD_WP); #else return false; #endif }
Will always return false without CONFIG_PTE_MARKER_UFFD_WP.
But make_uffd_wp_pte() might just happily place an entry. Hm.
The following might fix the problem:
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 51e0ec658457..ae1cf19918d3 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1830,8 +1830,10 @@ static void make_uffd_wp_pte(struct vm_area_struct *vma, ptent = pte_swp_mkuffd_wp(ptent); set_pte_at(vma->vm_mm, addr, pte, ptent); } else { +#ifdef CONFIG_PTE_MARKER_UFFD_WP set_pte_at(vma->vm_mm, addr, pte, make_pte_marker(PTE_MARKER_UFFD_WP)); +#endif } }
But I am *pretty* sure that that whole machinery should be fenced off. It does make 0 sense to mess with uffd-wp if there is no uffd-wp support.
-- Cheers,
David / dhildenb
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