[PATCH 1/2] bpf: support access variable length array of integer type

From: Feng zhou <zhoufeng.zf@bytedance.com>
To: martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, song@kernel.org, yhs@fb.com,
	john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
	haoluo@google.com, jolsa@kernel.org, davem@davemloft.net,
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
	mykolal@fb.com, shuah@kernel.org
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
	yangzhenze@bytedance.com, wangdongdong.6@bytedance.com,
	zhouchengming@bytedance.com, zhoufeng.zf@bytedance.com
Subject: [PATCH 1/2] bpf: support access variable length array of integer type
Date: Mon, 17 Apr 2023 16:07:48 +0800	[thread overview]
Message-ID: <20230417080749.39074-2-zhoufeng.zf@bytedance.com> (raw)
In-Reply-To: <20230417080749.39074-1-zhoufeng.zf@bytedance.com>

From: Feng Zhou <zhoufeng.zf@bytedance.com>

After this commit:
bpf: Support variable length array in tracing programs (9c5f8a1008a1)
Trace programs can access variable length array, but for structure
type. This patch adds support for integer type.

Example:
Hook load_balance
struct sched_domain {
	...
	unsigned long span[];
}

The access: sd->span[0].

Co-developed-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 kernel/bpf/btf.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 027f9f8a3551..a0887ee44e89 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6157,11 +6157,13 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
 		if (off < moff)
 			goto error;
 
-		/* Only allow structure for now, can be relaxed for
-		 * other types later.
-		 */
+		/* allow structure and integer */
 		t = btf_type_skip_modifiers(btf, array_elem->type,
 					    NULL);
+
+		if (btf_type_is_int(t))
+			return WALK_SCALAR;
+
 		if (!btf_type_is_struct(t))
 			goto error;
 
-- 
2.20.1

