linux-kernel - [PATCH v6 4/5] bpf/verifier: allow using bpf_kptr_xchg even if the MEM

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Message-ID: <20260208024846.18653-5-pilgrimtao@gmail.com>
Date: Sun,  8 Feb 2026 10:48:45 +0800
From: Chengkaitao <pilgrimtao@...il.com>
To: ast@...nel.org,
	daniel@...earbox.net,
	john.fastabend@...il.com,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	shuah@...nel.org,
	yangfeng@...inos.cn,
	alexei.starovoitov@...il.com
Cc: linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Kaitao Cheng <chengkaitao@...inos.cn>
Subject: [PATCH v6 4/5] bpf/verifier: allow using bpf_kptr_xchg even if the MEM_RCU flag is set

From: Kaitao Cheng <chengkaitao@...inos.cn>

For the following scenario:
    struct tree_node {
	struct bpf_refcount ref;
	struct bpf_rb_node node;
	struct node_data __kptr * node_data;
	u64 key;
    };
This means node_data would have the type PTR_TO_BTF_ID | MEM_ALLOC |
NON_OWN_REF | MEM_RCU.

When traversing an rbtree using bpf_rbtree_left/right, if we need to
use bpf_kptr_xchg to read the __kptr pointer, we still need to follow
the remove-read-add sequence.

This patch allows us to use bpf_kptr_xchg to directly read the __kptr
pointer without any prior operations.

Signed-off-by: Kaitao Cheng <chengkaitao@...inos.cn>
Signed-off-by: Feng Yang <yangfeng@...inos.cn>
---
 kernel/bpf/verifier.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bb3ff4bbb3a2..50cb4956e5bb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9261,7 +9261,8 @@ static const struct bpf_reg_types kptr_xchg_dest_types = {
 	.types = {
 		PTR_TO_MAP_VALUE,
 		PTR_TO_BTF_ID | MEM_ALLOC,
-		PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF
+		PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF,
+		PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU
 	}
 };
 static const struct bpf_reg_types dynptr_types = {
@@ -9422,6 +9423,7 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	case PTR_TO_BTF_ID | MEM_ALLOC:
 	case PTR_TO_BTF_ID | MEM_PERCPU | MEM_ALLOC:
 	case PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF:
+	case PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU:
 		if (meta->func_id != BPF_FUNC_spin_lock && meta->func_id != BPF_FUNC_spin_unlock &&
 		    meta->func_id != BPF_FUNC_kptr_xchg) {
 			verifier_bug(env, "unimplemented handling of MEM_ALLOC");
-- 
2.50.1 (Apple Git-155)