Lockless access to pte in pagemap_pte_range() might race with page migration
and trigger BUG_ON(!PageLocked()) in migration_entry_to_page():
CPU A (pagemap) CPU B (migration)
lock_page()
try_to_unmap(page, TTU_MIGRATION...)
make_migration_entry()
set_pte_at()
<read *pte>
pte_to_pagemap_entry()
remove_migration_ptes()
unlock_page()
if(is_migration_entry())
migration_entry_to_page()
BUG_ON(!PageLocked(page))
Also lockless read might be non-atomic if pte is larger than wordsize.
Other pte walkers (smaps, numa_maps, clear_refs) already lock ptes.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Reported-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
Fixes: 052fb0d635df ("proc: report file/anon bit in /proc/pid/pagemap")
Cc: Stable <stable@xxxxxxxxxxxxxxx> (v3.5+)
---
------------[ cut here ]------------
kernel BUG at ../include/linux/swapops.h:131!
invalid opcode: 0000 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 702 Comm: a.out Not tainted 3.19.0-rc1+ #16
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org
04/01/2014
task: ffff880001dc0dc0 ti: ffff88003dbd0000 task.ti: ffff88003dbd0000
RIP: pagemap_pte_range (include/linux/swapops.h:131 fs/proc/task_mmu.c:1136)
RSP: 0018:ffff88003dbd3d08 EFLAGS: 00010246
RAX: ffffea0000492b00 RBX: ffff88003dbd3e60 RCX: ffff880013bbe878
RDX: 0000000000000000 RSI: 000000000000001f RDI: 3e00000000000000
RBP: ffff88003dbd3d78 R08: 000000000024959f R09: ffff880001f5d000
R10: 0000000000000000 R11: 007fffffffffffff R12: 00007f6662000000
R13: ffff880001f5d000 R14: 00007f6661e8f000 R15: 0600000000000000
FS: 00007f666381d700(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f666333a520 CR3: 0000000013b7f000 CR4: 00000000000407b0
Stack:
0000000000000000 0000000062000000 ffff88003dbd3e78 ffff880013bbe878
007fffffffffffff 000000000003f65d ffffffff810d3710 0000000000000010
ffff88003dbd3d68 ffff88003dbd3e78 00007f6662000000 00007f6661e62000
Call Trace:
? find_vma (mm/mmap.c:2046)
walk_page_range (mm/pagewalk.c:51 mm/pagewalk.c:92 mm/pagewalk.c:241)
pagemap_read (fs/proc/task_mmu.c:1297)
? pid_maps_open (fs/proc/task_mmu.c:1068)
? m_stop (kernel/module.c:621)
__vfs_read (fs/read_write.c:430)
vfs_read (fs/read_write.c:455)
SyS_pread64 (fs/read_write.c:619 fs/read_write.c:606)
system_call_fastpath (arch/x86/kernel/entry_64.S:423)
Code: a0 4c 89 f6 48 8b 78 30 e8 a1 10 f9 ff 48 8b 4d b8 49 89 c4 e9
6d fc ff ff 0f 1f 44 00 00 49 39 ce 73 17 48 89 cf e9 7b fc ff ff <0f>
0b 4c 89 c7 e8 a9 bc f9 ff e9 ea fb ff ff 44 8b 55 9c 44 89
All code
========
0: a0 4c 89 f6 48 8b 78 movabs 0xe830788b48f6894c,%al
7: 30 e8
9: a1 10 f9 ff 48 8b 4d movabs 0x49b84d8b48fff910,%eax
10: b8 49
12: 89 c4 mov %eax,%esp
14: e9 6d fc ff ff jmpq 0xfffffffffffffc86
19: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
1e: 49 39 ce cmp %rcx,%r14
21: 73 17 jae 0x3a
23: 48 89 cf mov %rcx,%rdi
26: e9 7b fc ff ff jmpq 0xfffffffffffffca6
2b:* 0f 0b ud2 <-- trapping instruction
2d: 4c 89 c7 mov %r8,%rdi
30: e8 a9 bc f9 ff callq 0xfffffffffff9bcde
35: e9 ea fb ff ff jmpq 0xfffffffffffffc24
3a: 44 8b 55 9c mov -0x64(%rbp),%r10d
3e: 44 rex.R
3f: 89 .byte 0x89
Code starting with the faulting instruction
===========================================
0: 0f 0b ud2
2: 4c 89 c7 mov %r8,%rdi
5: e8 a9 bc f9 ff callq 0xfffffffffff9bcb3
a: e9 ea fb ff ff jmpq 0xfffffffffffffbf9
f: 44 8b 55 9c mov -0x64(%rbp),%r10d
13: 44 rex.R
14: 89 .byte 0x89
RIP pagemap_pte_range (include/linux/swapops.h:131 fs/proc/task_mmu.c:1136)
RSP <ffff88003dbd3d08>
------------[ cut here ]------------
---
fs/proc/task_mmu.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2464367..ff65557 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1070,7 +1070,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
struct vm_area_struct *vma;
struct pagemapread *pm = walk->private;
spinlock_t *ptl;
- pte_t *pte;
+ pte_t *pte, *orig_pte;
int err = 0;
/* find the first VMA at or above 'addr' */
@@ -1131,15 +1131,19 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
BUG_ON(is_vm_hugetlb_page(vma));
/* Addresses in the VMA. */
- for (; addr < min(end, vma->vm_end); addr += PAGE_SIZE) {
+ orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ for (; addr < min(end, vma->vm_end); pte++, addr += PAGE_SIZE) {
pagemap_entry_t pme;
- pte = pte_offset_map(pmd, addr);
+
pte_to_pagemap_entry(&pme, pm, vma, addr, *pte);
- pte_unmap(pte);
err = add_to_pagemap(addr, &pme, pm);
if (err)
- return err;
+ break;
}
+ pte_unmap_unlock(orig_pte, ptl);
+
+ if (err)
+ return err;
if (addr == end)
break;
--
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