From 34dd3bad1a6f1dc7d18ee8dd53f1d31bffd2aee8 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Fri, 2 Sep 2022 14:10:47 -0700 Subject: [PATCH] bpf: Relax the requirement to use preallocated hash maps in tracing progs. 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 Signed-off-by: Daniel Borkmann Acked-by: Kumar Kartikeya Dwivedi Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220902211058.60789-6-alexei.starovoitov@gmail.com --- kernel/bpf/verifier.c | 31 ++++++++++++++++++++++--------- 1 file changed, 22 insertions(+), 9 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 0194a36..3dce316 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -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)) { -- 2.7.4