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bpf: Replace open coded recursion prevention in sys_bpf()

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The required protection is that the caller cannot be migrated to a
different CPU as these functions end up in places which take either a hash
bucket lock or might trigger a kprobe inside the memory allocator. Both
scenarios can lead to deadlocks. The deadlock prevention is per CPU by
incrementing a per CPU variable which temporarily blocks the invocation of
BPF programs from perf and kprobes.

Replace the open coded preempt_[dis|en]able and __this_cpu_[inc|dec] pairs
with the new helper functions. These functions are already prepared to make
BPF work on PREEMPT_RT enabled kernels. No functional change for !RT
kernels.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145644.317843926@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-02-24 15:01:49 +01:00 committed by Alexei Starovoitov
parent 085fee1a72
commit b6e5dae15a
1 changed files with 8 additions and 19 deletions
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27
kernel/bpf/syscall.c
View file

@ -171,11 +171,7 @@ static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key,
flags);
}
/* must increment bpf_prog_active to avoid kprobe+bpf triggering from
* inside bpf map update or delete otherwise deadlocks are possible
*/
preempt_disable();
__this_cpu_inc(bpf_prog_active);
bpf_disable_instrumentation();
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
err = bpf_percpu_hash_update(map, key, value, flags);
@ -206,8 +202,7 @@ static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key,
err = map->ops->map_update_elem(map, key, value, flags);
rcu_read_unlock();
}
__this_cpu_dec(bpf_prog_active);
preempt_enable();
bpf_enable_instrumentation();
maybe_wait_bpf_programs(map);
return err;
@ -222,8 +217,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
if (bpf_map_is_dev_bound(map))
return bpf_map_offload_lookup_elem(map, key, value);
preempt_disable();
this_cpu_inc(bpf_prog_active);
bpf_disable_instrumentation();
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
err = bpf_percpu_hash_copy(map, key, value);
@ -268,8 +262,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
rcu_read_unlock();
}
this_cpu_dec(bpf_prog_active);
preempt_enable();
bpf_enable_instrumentation();
maybe_wait_bpf_programs(map);
return err;
@ -1136,13 +1129,11 @@ static int map_delete_elem(union bpf_attr *attr)
goto out;
}
preempt_disable();
__this_cpu_inc(bpf_prog_active);
bpf_disable_instrumentation();
rcu_read_lock();
err = map->ops->map_delete_elem(map, key);
rcu_read_unlock();
__this_cpu_dec(bpf_prog_active);
preempt_enable();
bpf_enable_instrumentation();
maybe_wait_bpf_programs(map);
out:
kfree(key);
@ -1254,13 +1245,11 @@ int generic_map_delete_batch(struct bpf_map *map,
break;
}
preempt_disable();
__this_cpu_inc(bpf_prog_active);
bpf_disable_instrumentation();
rcu_read_lock();
err = map->ops->map_delete_elem(map, key);
rcu_read_unlock();
__this_cpu_dec(bpf_prog_active);
preempt_enable();
bpf_enable_instrumentation();
maybe_wait_bpf_programs(map);
if (err)
break;