Hi,
在 2021/12/20 22:15, David Hildenbrand 写道:
On 20.12.21 14:18, Eric Ren wrote:
`mb_id` is unsigned integer, which is used to index
`mb_states` array in reverse order. `mb_id` can decrease
to `0UL - 1` that is a very large number, causing invalid
address access.
Hi Eric,
thanks for your report!
The only way I can see this happening would be if
next_mb_id == 0, in which case we would get
_mb_id = _vm->sbm.next_mb_id - 1
-> _mb_id = 0 - 1 = -1ULL
In the for loop, eg.
_vm->sbm.next_mb_id == 756
initial _mb_id = 755
_vm->sbm.first_mb_id == 0
_vm->sbm.mb_count[_state] == 1
_mb_id-- will decrease to 0, * at this time *, the condition below in loop is true:
_mb_id >= _vm->sbm.first_mb_id && _vm->sbm.mb_count[_state];
in next iteration, _mb_id-- results in _mb_id == -1UL. -1UL > _vm->sbm.first_mb_id
is true, then the condition is still true. There, we have a invalid mb_id number.
Otherwise we should always stay above _vm->sbm.first_mb_id.
Am I correct or am I missing something?
But in that case we would have to have
vm->sbm.first_mb_id == 0
and consequently the start address of the device would have to be at
address 0.
... but that does sound very weird, especially on x86_64?
Do you have details about the device layout / position in guest physical
address space?
Hope I've explained it clearly above :-)
virtio_mem_bbm_for_each_bb_rev() would need a similar fix.
Oh yes, thanks!
Eric
The calltrace is like below:
```
[ 286.344977] BUG: unable to handle page fault for address: ffffa95180cf8fff
[ 286.345800] #PF: supervisor read access in kernel mode
[ 286.346738] #PF: error_code(0x0000) - not-present page
[ 286.347440] PGD 1000067 P4D 1000067 PUD 138c067 PMD 1840435067 PTE 0
[ 286.348156] Oops: 0000 [#1] SMP PTI [ 286.348556] CPU: 1 PID: 122 Comm: kworker/1:2 Tainted: G OE
...
[ 286.350740] Workqueue: events_freezable virtio_mem_run_wq [virtio_mem]
[ 286.351605] RIP: 0010:virtio_mem_unplug_request+0x418/0x890 [virtio_mem]
[ 286.352519] Code: 0f 87 fc 00 00 00 4a 63 54 ac 30 48 83 bc d5 f8 00 00 00 00 48 89 d0 0f 8
4 e5 00 00 00 48 8b b5 38 01 00 00 4c 89 e2 48 29 ca <0f> b6 34 16 39 c6 75 c7 40 80 fe 02 0f
82 a4 01 00 00 40 80 fe 03
[ 286.355030] RSP: 0018:ffffa95181c4bd50 EFLAGS: 00010286
[ 286.355737] RAX: 0000000000000005 RBX: 0000000000006100 RCX: 0000000000000000
[ 286.356752] RDX: ffffffffffffffff RSI: ffffa95180cf9000 RDI: ffff8e5dc393b348
[ 286.357649] RBP: ffff8e5dc393b200 R08: ffff8e463cd2b610 R09: 0000000000000021
[ 286.358627] R10: ffffa95181c4bcd0 R11: ffffa95181c4baa0 R12: ffffffffffffffff
[ 286.359617] R13: 0000000000000003 R14: ffff8e5dc393b348 R15: 00000000fffffff0
[ 286.360503] FS: 0000000000000000(0000) GS:ffff8e463cd00000(0000) knlGS:0000000000000000
[ 286.361532] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 286.362229] CR2: ffffa95180cf8fff CR3: 0000001846234000 CR4: 00000000000006e0
[ 286.363168] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 286.364162] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 286.365054] Call Trace:
[ 286.365431] ? virtio_mem_run_wq+0x5a4/0x870 [virtio_mem]
[ 286.366132] ? __schedule+0x4b3/0x800
[ 286.366547] ? process_one_work+0x18b/0x350
[ 286.367041] ? worker_thread+0x4f/0x3a0
[ 286.367675] ? rescuer_thread+0x350/0x350
[ 286.368234] ? kthread+0xfa/0x130
[ 286.368605] ? kthread_create_worker_on_cpu+0x70/0x70
[ 286.369155] ? ret_from_fork+0x1f/0x30
```
Fixes by also checking its up boundary.
Signed-off-by: Eric Ren <renzhengeek@xxxxxxxxx>
--
v2: Correct the SOB
Use _vm and remove duplicated spaces
---
drivers/virtio/virtio_mem.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 96e5a8782769..f1ba0dadd47a 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -486,7 +486,9 @@ static int virtio_mem_sbm_mb_states_prepare_next_mb(struct virtio_mem *vm)
#define virtio_mem_sbm_for_each_mb_rev(_vm, _mb_id, _state) \
for (_mb_id = _vm->sbm.next_mb_id - 1; \
- _mb_id >= _vm->sbm.first_mb_id && _vm->sbm.mb_count[_state]; \
+ _mb_id >= _vm->sbm.first_mb_id && \
+ _mb_id < _vm->sbm.next_mb_id && \
+ _vm->sbm.mb_count[_state]; \
_mb_id--) \
if (virtio_mem_sbm_get_mb_state(_vm, _mb_id) == _state)
