Sysbot discovered that the queue and stack maps can deadlock if they are
being used from a BPF program that can be called from NMI context (such as
one that is attached to a perf HW counter event). To fix this, add an
in_nmi() check and use raw_spin_trylock() in NMI context, erroring out if
grabbing the lock fails.
Fixes: f1a2e44a3aec ("bpf: add queue and stack maps")
Reported-by: Hsin-Wei Hung <hsinweih@xxxxxxx>
Tested-by: Hsin-Wei Hung <hsinweih@xxxxxxx>
Co-developed-by: Hsin-Wei Hung <hsinweih@xxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
---
kernel/bpf/queue_stack_maps.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
index 8d2ddcb7566b..d869f51ea93a 100644
--- a/kernel/bpf/queue_stack_maps.c
+++ b/kernel/bpf/queue_stack_maps.c
@@ -98,7 +98,12 @@ static long __queue_map_get(struct bpf_map *map, void *value, bool delete)
int err = 0;
void *ptr;
- raw_spin_lock_irqsave(&qs->lock, flags);
+ if (in_nmi()) {
+ if (!raw_spin_trylock_irqsave(&qs->lock, flags))
+ return -EBUSY;
+ } else {
+ raw_spin_lock_irqsave(&qs->lock, flags);
+ }
if (queue_stack_map_is_empty(qs)) {
memset(value, 0, qs->map.value_size);
@@ -128,7 +133,12 @@ static long __stack_map_get(struct bpf_map *map, void *value, bool delete)
void *ptr;
u32 index;
- raw_spin_lock_irqsave(&qs->lock, flags);
+ if (in_nmi()) {
+ if (!raw_spin_trylock_irqsave(&qs->lock, flags))
+ return -EBUSY;
+ } else {
+ raw_spin_lock_irqsave(&qs->lock, flags);
+ }
if (queue_stack_map_is_empty(qs)) {
memset(value, 0, qs->map.value_size);
@@ -193,7 +203,12 @@ static long queue_stack_map_push_elem(struct bpf_map *map, void *value,
if (flags & BPF_NOEXIST || flags > BPF_EXIST)
return -EINVAL;
- raw_spin_lock_irqsave(&qs->lock, irq_flags);
+ if (in_nmi()) {
+ if (!raw_spin_trylock_irqsave(&qs->lock, irq_flags))
+ return -EBUSY;
+ } else {
+ raw_spin_lock_irqsave(&qs->lock, irq_flags);
+ }
if (queue_stack_map_is_full(qs)) {
if (!replace) {
--
2.42.0
