bpf: Remove tracing program restriction on map types

The hash map is now fully converted to bpf_mem_alloc. Its implementation is not
allocating synchronously and not calling call_rcu() directly. It's now safe to
use non-preallocated hash maps in all types of tracing programs including
BPF_PROG_TYPE_PERF_EVENT that runs out of NMI context.
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/20220902211058.60789-13-alexei.starovoitov@gmail.com

kernel/bpf/verifier.c

@@ -12623,48 +12623,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(prog);
-	/*
-	 * Validate that trace type programs use preallocated hash maps.
-	 *
-	 * For programs attached to PERF events this is mandatory as the
-	 * perf NMI can hit any arbitrary code sequence.
-	 *
-	 * 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
-	 * !RT kernels it is allowed for backwards compatibility reasons for
-	 * now, but warnings are emitted so developers are made aware of
-	 * the unsafety and can fix their programs before this is enforced.
-	 */
-	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 (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");
-		}
-	}
 
 	if (map_value_has_spin_lock(map)) {
 		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {