bpf: Remove tracing program restriction on map types

[ Upstream commit 96da3f7d489d11b43e7c1af90d876b9a2492cca8 ]

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.

---
 kernel/bpf/verifier.c | 29 -----------------------------
 1 file changed, 29 deletions(-)

index 7049a85a78ab..77a75ccaae5e 100644
@@ -11700,35 +11700,6 @@ 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 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.
-	 *
-	 * 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) {
-			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;
-		}
-		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)) {
 		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {

2.49.0

what kernel tree(s) is this for?

This backport is for v5.15.y stable version. My bad, I should have mentioned it in the subject.

Nack.

5.15 doesn't have bpf_mem_alloc.
This backport makes no sense.

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected. No action required from the submitter.

The upstream commit SHA1 provided is correct: 96da3f7d489d11b43e7c1af90d876b9a2492cca8

WARNING: Author mismatch between patch and upstream commit:
Backport author: Devaansh Kumar<[email protected]> Commit author: Alexei Starovoitov<[email protected]>

Note: The patch differs from the upstream commit:
---

1:  96da3f7d489d1 < -:  ------------- bpf: Remove tracing program restriction on map types
-:  ------------- > 1:  9bc5c94e278f7 Linux 6.14.2

---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.14.y       |  Success    |  Success   |
| stable/linux-6.13.y       |  Success    |  Success   |
| stable/linux-6.12.y       |  Success    |  Success   |
| stable/linux-6.6.y        |  Success    |  Success   |
| stable/linux-6.1.y        |  Success    |  Success   |
| stable/linux-5.15.y       |  Success    |  Success   |
| stable/linux-5.10.y       |  Success    |  Success   |
| stable/linux-5.4.y        |  Success    |  Success   |