From 5861d1e8dbc4e1a03ebffb96ac041026cdd34c07 Mon Sep 17 00:00:00 2001 From: Dave Marchevsky Date: Mon, 21 Aug 2023 12:33:10 -0700 Subject: [PATCH] bpf: Allow bpf_spin_{lock,unlock} in sleepable progs Commit 9e7a4d9831e8 ("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: Dave Marchevsky Link: https://lore.kernel.org/r/20230821193311.3290257-7-davemarchevsky@fb.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/helpers.c | 2 ++ kernel/bpf/verifier.c | 9 +++------ 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 945a85e..8bd3812 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -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 diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4b638eb..bb78212 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5064,7 +5064,9 @@ bad_type: */ 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)) { -- 2.7.4