Commit 5861d1e8 authored by Dave Marchevsky's avatar Dave Marchevsky Committed by Alexei Starovoitov
Browse files

bpf: Allow bpf_spin_{lock,unlock} in sleepable progs 



Commit 9e7a4d98 ("bpf: Allow LSM programs to use bpf spin locks")
disabled bpf_spin_lock usage in sleepable progs, stating:

 Sleepable LSM programs can be preempted which means that allowng spin
 locks will need more work (disabling preemption and the verifier
 ensuring that no sleepable helpers are called when a spin lock is
 held).

This patch disables preemption before grabbing bpf_spin_lock. The second
requirement above "no sleepable helpers are called when a spin lock is
held" is implicitly enforced by current verifier logic due to helper
calls in spin_lock CS being disabled except for a few exceptions, none
of which sleep.

Due to above preemption changes, bpf_spin_lock CS can also be considered
a RCU CS, so verifier's in_rcu_cs check is modified to account for this.

Signed-off-by: default avatarDave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230821193311.3290257-7-davemarchevsky@fb.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 0816b8c6

kernel/bpf/helpers.c

+2 −0
Original line number Diff line number Diff line
@@ -286,6 +286,7 @@ static inline void __bpf_spin_lock(struct bpf_spin_lock *lock) 
	compiletime_assert(u.val == 0, "__ARCH_SPIN_LOCK_UNLOCKED not 0");

	BUILD_BUG_ON(sizeof(*l) != sizeof(__u32));

	BUILD_BUG_ON(sizeof(*lock) != sizeof(__u32));

	preempt_disable();

	arch_spin_lock(l);

}
@@ -294,6 +295,7 @@ static inline void __bpf_spin_unlock(struct bpf_spin_lock *lock) 
	arch_spinlock_t *l = (void *)lock;



	arch_spin_unlock(l);

	preempt_enable();

}



#else

kernel/bpf/verifier.c

+3 −6
Original line number Diff line number Diff line
@@ -5064,7 +5064,9 @@ static int map_kptr_match_type(struct bpf_verifier_env *env, 
 */

static bool in_rcu_cs(struct bpf_verifier_env *env)

{

	return env->cur_state->active_rcu_lock || !env->prog->aux->sleepable;

	return env->cur_state->active_rcu_lock ||

	       env->cur_state->active_lock.ptr ||

	       !env->prog->aux->sleepable;

}









/* Once GCC supports btf_type_tag the following mechanism will be replaced with tag check */








@@ -16975,11 +16977,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,







			verbose(env, "tracing progs cannot use bpf_spin_lock yet\n");









			return -EINVAL;









		}

















		if (prog->aux->sleepable) {









			verbose(env, "sleepable progs cannot use bpf_spin_lock yet\n");









			return -EINVAL;









		}









	}

















	if (btf_record_has_field(map->record, BPF_TIMER)) {