On 15.11.23 23:00, Andrew Morton wrote:
On Wed, 15 Nov 2023 05:32:19 -0800 syzbot <syzbot+7ca4b2719dc742b8d0a4@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxx
Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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
