netdev - [PATCH bpf-next 4/4] bpf, btf: Enforce destructor kfunc type with CFI

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Message-ID: <20250724223225.1481960-10-samitolvanen@google.com>
Date: Thu, 24 Jul 2025 22:32:30 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: bpf@...r.kernel.org
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH bpf-next 4/4] bpf, btf: Enforce destructor kfunc type with CFI

Ensure that registered destructor kfuncs have the same type
as btf_dtor_kfunc_t to avoid a kernel panic on systems with
CONFIG_CFI_CLANG enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 kernel/bpf/btf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0aff814cb53a..2b0ebd46db4a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8856,6 +8856,13 @@ static int btf_check_dtor_kfuncs(struct btf *btf, const struct btf_id_dtor_kfunc
 		 */
 		if (!t || !btf_type_is_ptr(t))
 			return -EINVAL;
+
+		if (IS_ENABLED(CONFIG_CFI_CLANG)) {
+			/* Ensure the destructor kfunc type matches btf_dtor_kfunc_t */
+			t = btf_type_by_id(btf, t->type);
+			if (!btf_type_is_void(t))
+				return -EINVAL;
+		}
 	}
 	return 0;
 }
-- 
2.50.1.470.g6ba607880d-goog