[PATCH 0/2] Access variable length array relaxed for integer type

[PATCH 0/2] Access variable length array relaxed for integer type

[Feng zhou]

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

Add support for integer type of accessing variable length array.
Add a selftest to check it.

Feng Zhou (2):
  bpf: support access variable length array of integer type
  selftests/bpf: Add test to access integer type of variable array

 kernel/bpf/btf.c                              |  8 +++++---
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 20 +++++++++++++++++++
 .../selftests/bpf/prog_tests/tracing_struct.c |  2 ++
 .../selftests/bpf/progs/tracing_struct.c      | 13 ++++++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

-- 
2.20.1

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

[Feng zhou]

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

[PATCH 2/2] selftests/bpf: Add test to access integer type of variable array

[Feng zhou]

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

Add prog test for accessing integer type of variable array in tracing
program.

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>
---
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 20 +++++++++++++++++++
 .../selftests/bpf/prog_tests/tracing_struct.c |  2 ++
 .../selftests/bpf/progs/tracing_struct.c      | 13 ++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index fe847ebfb731..52785ba671e6 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -28,6 +28,11 @@ struct bpf_testmod_struct_arg_2 {
 	long b;
 };
 
+struct bpf_testmod_struct_arg_3 {
+	int a;
+	int b[];
+};
+
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in bpf_testmod.ko BTF");
@@ -63,6 +68,12 @@ bpf_testmod_test_struct_arg_5(void) {
 	return bpf_testmod_test_struct_arg_result;
 }
 
+noinline int
+bpf_testmod_test_struct_arg_6(struct bpf_testmod_struct_arg_3 *a) {
+	bpf_testmod_test_struct_arg_result = a->b[0];
+	return bpf_testmod_test_struct_arg_result;
+}
+
 __bpf_kfunc void
 bpf_testmod_test_mod_kfunc(int i)
 {
@@ -195,6 +206,7 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 	};
 	struct bpf_testmod_struct_arg_1 struct_arg1 = {10};
 	struct bpf_testmod_struct_arg_2 struct_arg2 = {2, 3};
+	struct bpf_testmod_struct_arg_3 *struct_arg3;
 	int i = 1;
 
 	while (bpf_testmod_return_ptr(i))
@@ -206,6 +218,14 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 	(void)bpf_testmod_test_struct_arg_4(struct_arg1, 1, 2, 3, struct_arg2);
 	(void)bpf_testmod_test_struct_arg_5();
 
+	struct_arg3 = kmalloc((sizeof(struct bpf_testmod_struct_arg_3) +
+				sizeof(int)), GFP_KERNEL);
+	if (struct_arg3 != NULL) {
+		struct_arg3->b[0] = 1;
+		(void)bpf_testmod_test_struct_arg_6(struct_arg3);
+		kfree(struct_arg3);
+	}
+
 	/* This is always true. Use the check to make sure the compiler
 	 * doesn't remove bpf_testmod_loop_test.
 	 */
diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_struct.c b/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
index 48dc9472e160..1c75a32186d6 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
@@ -53,6 +53,8 @@ static void test_fentry(void)
 
 	ASSERT_EQ(skel->bss->t5_ret, 1, "t5 ret");
 
+	ASSERT_EQ(skel->bss->t6, 1, "t6 ret");
+
 	tracing_struct__detach(skel);
 destroy_skel:
 	tracing_struct__destroy(skel);
diff --git a/tools/testing/selftests/bpf/progs/tracing_struct.c b/tools/testing/selftests/bpf/progs/tracing_struct.c
index e718f0ebee7d..c435a3a8328a 100644
--- a/tools/testing/selftests/bpf/progs/tracing_struct.c
+++ b/tools/testing/selftests/bpf/progs/tracing_struct.c
@@ -13,12 +13,18 @@ struct bpf_testmod_struct_arg_2 {
 	long b;
 };
 
+struct bpf_testmod_struct_arg_3 {
+	int a;
+	int b[];
+};
+
 long t1_a_a, t1_a_b, t1_b, t1_c, t1_ret, t1_nregs;
 __u64 t1_reg0, t1_reg1, t1_reg2, t1_reg3;
 long t2_a, t2_b_a, t2_b_b, t2_c, t2_ret;
 long t3_a, t3_b, t3_c_a, t3_c_b, t3_ret;
 long t4_a_a, t4_b, t4_c, t4_d, t4_e_a, t4_e_b, t4_ret;
 long t5_ret;
+int t6;
 
 SEC("fentry/bpf_testmod_test_struct_arg_1")
 int BPF_PROG2(test_struct_arg_1, struct bpf_testmod_struct_arg_2, a, int, b, int, c)
@@ -117,4 +123,11 @@ int BPF_PROG2(test_struct_arg_10, int, ret)
 	return 0;
 }
 
+SEC("fentry/bpf_testmod_test_struct_arg_6")
+int BPF_PROG2(test_struct_arg_11, struct bpf_testmod_struct_arg_3 *, a)
+{
+	t6 = a->b[0];
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.20.1

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

[Alexei Starovoitov]

On Mon, Apr 17, 2023 at 04:07:48PM +0800, Feng zhou wrote:
> 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].

The use case makes sense.
Please add it as a selftest. Either combine it with patch 2 or another patch 3.
and then resubmit.
Make sure to use [PATCH bpf-next] subject, so BPF CI knows how to test it.

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

[Feng Zhou]

在 2023/4/18 08:08, Alexei Starovoitov 写道:
> On Mon, Apr 17, 2023 at 04:07:48PM +0800, Feng zhou wrote:
>> 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].
> The use case makes sense.
> Please add it as a selftest. Either combine it with patch 2 or another patch 3.
> and then resubmit.
> Make sure to use [PATCH bpf-next] subject, so BPF CI knows how to test it.

Will do, thanks.