linux-kernel - [PATCH] bpf: Remove tracing program restriction on map types

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Message-ID: <20250415130910.2326537-1-devaanshk840@gmail.com>
Date: Tue, 15 Apr 2025 18:39:07 +0530
From: Devaansh Kumar <devaanshk840@...il.com>
To: gregkh@...uxfoundation.org,
	sashal@...nel.org,
	stable@...r.kernel.org,
	ast@...nel.org,
	daniel@...earbox.net
Cc: Devaansh Kumar <devaanshk840@...il.com>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linuxfoundation.org,
	Kumar Kartikeya Dwivedi <memxor@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>
Subject: [PATCH] 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.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
Acked-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/bpf/20220902211058.60789-13-alexei.starovoitov@gmail.com
Signed-off-by: Devaansh Kumar <devaanshk840@...il.com>
---
 kernel/bpf/verifier.c | 29 -----------------------------
 1 file changed, 29 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7049a85a78ab..77a75ccaae5e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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