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

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3dce316..57ec06b 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/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) {