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Subject[PATCH 5.8 70/99] mm: validate pmd after splitting
Date
From: Minchan Kim <minchan@kernel.org>

[ Upstream commit ce2684254bd4818ca3995c0d021fb62c4cf10a19 ]

syzbot reported the following KASAN splat:

general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 1 PID: 6826 Comm: syz-executor142 Not tainted 5.9.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__lock_acquire+0x84/0x2ae0 kernel/locking/lockdep.c:4296
Code: ff df 8a 04 30 84 c0 0f 85 e3 16 00 00 83 3d 56 58 35 08 00 0f 84 0e 17 00 00 83 3d 25 c7 f5 07 00 74 2c 4c 89 e8 48 c1 e8 03 <80> 3c 30 00 74 12 4c 89 ef e8 3e d1 5a 00 48 be 00 00 00 00 00 fc
RSP: 0018:ffffc90004b9f850 EFLAGS: 00010006
Call Trace:
lock_acquire+0x140/0x6f0 kernel/locking/lockdep.c:5006
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:354 [inline]
madvise_cold_or_pageout_pte_range+0x52f/0x25c0 mm/madvise.c:389
walk_pmd_range mm/pagewalk.c:89 [inline]
walk_pud_range mm/pagewalk.c:160 [inline]
walk_p4d_range mm/pagewalk.c:193 [inline]
walk_pgd_range mm/pagewalk.c:229 [inline]
__walk_page_range+0xe7b/0x1da0 mm/pagewalk.c:331
walk_page_range+0x2c3/0x5c0 mm/pagewalk.c:427
madvise_pageout_page_range mm/madvise.c:521 [inline]
madvise_pageout mm/madvise.c:557 [inline]
madvise_vma mm/madvise.c:946 [inline]
do_madvise+0x12d0/0x2090 mm/madvise.c:1145
__do_sys_madvise mm/madvise.c:1171 [inline]
__se_sys_madvise mm/madvise.c:1169 [inline]
__x64_sys_madvise+0x76/0x80 mm/madvise.c:1169
do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The backing vma was shmem.

In case of split page of file-backed THP, madvise zaps the pmd instead
of remapping of sub-pages. So we need to check pmd validity after
split.

Reported-by: syzbot+ecf80462cb7d5d552bc7@syzkaller.appspotmail.com
Fixes: 1a4e58cce84e ("mm: introduce MADV_PAGEOUT")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/madvise.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index d4aa5f7765435..0e0d61003fc6f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -381,9 +381,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
return 0;
}

+regular_page:
if (pmd_trans_unstable(pmd))
return 0;
-regular_page:
#endif
tlb_change_page_size(tlb, PAGE_SIZE);
orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
--
2.25.1


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