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Thu, 22 Jan 2026 00:14:37 -0800 (PST) Received: from localhost.localdomain ([116.128.244.171]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a7190c9bdesm173868825ad.24.2026.01.22.00.14.31 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 22 Jan 2026 00:14:37 -0800 (PST) From: chengkaitao To: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Chengkaitao Subject: [PATCH] bpf/verifier: allow calling bpf_kptr_xchg while holding a lock Date: Thu, 22 Jan 2026 16:14:26 +0800 Message-ID: <20260122081426.78472-1-pilgrimtao@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Chengkaitao For the following scenario: struct tree_node { struct bpf_rb_node node; struct request __kptr *req; u64 key; }; struct bpf_rb_root tree_root __contains(tree_node, node); struct bpf_spin_lock tree_lock; If we need to traverse all nodes in the rbtree, retrieve the __kptr pointer from each node, and read kernel data from the referenced object, using bpf_kptr_xchg appears unavoidable. This patch skips the BPF verifier checks for bpf_kptr_xchg when called while holding a lock. Signed-off-by: Chengkaitao --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3135643d5695..05a6a6606b6c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -20387,7 +20387,8 @@ static int do_check_insn(struct bpf_verifier_env *e= nv, bool *do_print_state) =20 if (env->cur_state->active_locks) { if ((insn->src_reg =3D=3D BPF_REG_0 && - insn->imm !=3D BPF_FUNC_spin_unlock) || + insn->imm !=3D BPF_FUNC_spin_unlock && + insn->imm !=3D BPF_FUNC_kptr_xchg) || (insn->src_reg =3D=3D BPF_PSEUDO_KFUNC_CALL && (insn->off !=3D 0 || !kfunc_spin_allowed(insn->imm)))) { verbose(env, --=20 2.50.1 (Apple Git-155)