Commit a34a9f1a authored by Toke Høiland-Jørgensen's avatar Toke Høiland-Jørgensen Committed by Alexei Starovoitov
Browse files

bpf: Avoid deadlock when using queue and stack maps from NMI 



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: f1a2e44a ("bpf: add queue and stack maps")
Reported-by: default avatarHsin-Wei Hung <hsinweih@uci.edu>
Tested-by: default avatarHsin-Wei Hung <hsinweih@uci.edu>
Co-developed-by: default avatarHsin-Wei Hung <hsinweih@uci.edu>
Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20230911132815.717240-1-toke@redhat.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent b772b70b

kernel/bpf/queue_stack_maps.c

+18 −3
Original line number Diff line number Diff line
@@ -98,7 +98,12 @@ static long __queue_map_get(struct bpf_map *map, void *value, bool delete) 
	int err = 0;

	void *ptr;



	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;



	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;



	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) {