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bpf: Relax the requirement to use preallocated hash maps in tracing progs.

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Since bpf hash map was converted to use bpf_mem_alloc it is safe to use
from tracing programs and in RT kernels.
But per-cpu hash map is still using dynamic allocation for per-cpu map
values, hence keep the warning for this map type.
In the future alloc_percpu_gfp can be front-end-ed with bpf_mem_cache
and this restriction will be completely lifted.
perf_event (NMI) bpf programs have to use preallocated hash maps,
because free_htab_elem() is using call_rcu which might crash if re-entered.

Sleepable bpf programs have to use preallocated hash maps, because
life time of the map elements is not protected by rcu_read_lock/unlock.
This restriction can be lifted in the future as well.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220902211058.60789-6-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2022-09-02 14:10:47 -07:00 committed by Daniel Borkmann
parent 89dc8d0c38
commit 34dd3bad1a
1 changed files with 22 additions and 9 deletions
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31
kernel/bpf/verifier.c
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@ -12629,10 +12629,12 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
* For programs attached to PERF events this is mandatory as the
* perf NMI can hit any arbitrary code sequence.
*
* All other trace types using preallocated hash maps are unsafe as
* well because tracepoint or kprobes can be inside locked regions
* of the memory allocator or at a place where a recursion into the
* memory allocator would see inconsistent state.
* All other trace types using non-preallocated per-cpu hash maps are
* unsafe as well because tracepoint or kprobes can be inside locked
* regions of the per-cpu memory allocator or at a place where a
* recursion into the per-cpu memory allocator would see inconsistent
* state. Non per-cpu hash maps are using bpf_mem_alloc-tor which is
* safe to use from kprobe/fentry and in RT.
*
* On RT enabled kernels run-time allocation of all trace type
* programs is strictly prohibited due to lock type constraints. On
@ -12642,15 +12644,26 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
*/
if (is_tracing_prog_type(prog_type) && !is_preallocated_map(map)) {
if (prog_type == BPF_PROG_TYPE_PERF_EVENT) {
/* perf_event bpf progs have to use preallocated hash maps
* because non-prealloc is still relying on call_rcu to free
* elements.
*/
verbose(env, "perf_event programs can only use preallocated hash map\n");
return -EINVAL;
}
if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
verbose(env, "trace type programs can only use preallocated hash map\n");
return -EINVAL;
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
(map->inner_map_meta &&
map->inner_map_meta->map_type == BPF_MAP_TYPE_PERCPU_HASH)) {
if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
verbose(env,
"trace type programs can only use preallocated per-cpu hash map\n");
return -EINVAL;
}
WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
verbose(env,
"trace type programs with run-time allocated per-cpu hash maps are unsafe."
" Switch to preallocated hash maps.\n");
}
WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
verbose(env, "trace type programs with run-time allocated hash maps are unsafe. Switch to preallocated hash maps.\n");
}
if (map_value_has_spin_lock(map)) {