[PATCH bpf-next v6 0/4] Add prog_kfunc feature probe

[PATCH bpf-next v6 0/4] Add prog_kfunc feature probe

[Tao Chen]

More and more kfunc functions are being added to the kernel.
Different prog types have different restrictions when using kfunc.
Therefore, prog_kfunc probe is added to check whether it is supported,
and the use of this api will be added to bpftool later.

Change list:
- v5 -> v6:
  - remove fd_array_cnt
  - test case clean code
- v5
  https://lore.kernel.org/bpf/20250210055945.27192-1-chen.dylane@gmail.com

- v4 -> v5:
  - use fd_array on stack
  - declare the scope of use of btf_fd
- v4
  https://lore.kernel.org/bpf/20250206051557.27913-1-chen.dylane@gmail.com/

- v3 -> v4:
  - add fd_array init for kfunc in mod btf
  - add test case for kfunc in mod btf
  - refactor common part as prog load type check for
    libbpf_probe_bpf_{helper,kfunc}
- v3
  https://lore.kernel.org/bpf/20250124144411.13468-1-chen.dylane@gmail.com

- v2 -> v3:
  - rename parameter off with btf_fd
  - extract the common part for libbpf_probe_bpf_{helper,kfunc}
- v2
  https://lore.kernel.org/bpf/20250123170555.291896-1-chen.dylane@gmail.com

- v1 -> v2:
  - check unsupported prog type like probe_bpf_helper
  - add off parameter for module btf
  - check verifier info when kfunc id invalid
- v1
  https://lore.kernel.org/bpf/20250122171359.232791-1-chen.dylane@gmail.com

Tao Chen (4):
  libbpf: Extract prog load type check from libbpf_probe_bpf_helper
  libbpf: Init fd_array when prog probe load
  libbpf: Add libbpf_probe_bpf_kfunc API
  selftests/bpf: Add libbpf_probe_bpf_kfunc API selftests

 tools/lib/bpf/libbpf.h                        |  19 ++-
 tools/lib/bpf/libbpf.map                      |   1 +
 tools/lib/bpf/libbpf_probes.c                 |  84 ++++++++++---
 .../selftests/bpf/prog_tests/libbpf_probes.c  | 111 ++++++++++++++++++
 4 files changed, 200 insertions(+), 15 deletions(-)

-- 
2.43.0

[PATCH bpf-next v6 1/4] libbpf: Extract prog load type check from libbpf_probe_bpf_helper

[Tao Chen]

Extract prog load type check part from libbpf_probe_bpf_helper
suggested by Andrii, which will be used in both
libbpf_probe_bpf_{helper, kfunc}.

Signed-off-by: Tao Chen <chen.dylane@gmail.com>
---
 tools/lib/bpf/libbpf_probes.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index 9dfbe7750f56..aeb4fd97d801 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -413,6 +413,23 @@ int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void *opts)
 	return libbpf_err(ret);
 }
 
+static bool can_probe_prog_type(enum bpf_prog_type prog_type)
+{
+	/* we can't successfully load all prog types to check for BPF helper
+	 * and kfunc support.
+	 */
+	switch (prog_type) {
+	case BPF_PROG_TYPE_TRACING:
+	case BPF_PROG_TYPE_EXT:
+	case BPF_PROG_TYPE_LSM:
+	case BPF_PROG_TYPE_STRUCT_OPS:
+		return false;
+	default:
+		break;
+	}
+	return true;
+}
+
 int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
 			    const void *opts)
 {
@@ -427,18 +444,8 @@ int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helpe
 	if (opts)
 		return libbpf_err(-EINVAL);
 
-	/* we can't successfully load all prog types to check for BPF helper
-	 * support, so bail out with -EOPNOTSUPP error
-	 */
-	switch (prog_type) {
-	case BPF_PROG_TYPE_TRACING:
-	case BPF_PROG_TYPE_EXT:
-	case BPF_PROG_TYPE_LSM:
-	case BPF_PROG_TYPE_STRUCT_OPS:
+	if (!can_probe_prog_type(prog_type))
 		return -EOPNOTSUPP;
-	default:
-		break;
-	}
 
 	buf[0] = '\0';
 	ret = probe_prog_load(prog_type, insns, insn_cnt, buf, sizeof(buf));
-- 
2.43.0

[PATCH bpf-next v6 2/4] libbpf: Init fd_array when prog probe load

[Tao Chen]

fd_array used to store module btf fd, which will
be used for kfunc probe in module btf.

Signed-off-by: Tao Chen <chen.dylane@gmail.com>
---
 tools/lib/bpf/libbpf_probes.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index aeb4fd97d801..8ed92ea922b3 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -102,12 +102,13 @@ __u32 get_kernel_version(void)
 
 static int probe_prog_load(enum bpf_prog_type prog_type,
 			   const struct bpf_insn *insns, size_t insns_cnt,
-			   char *log_buf, size_t log_buf_sz)
+			   int *fd_array, char *log_buf, size_t log_buf_sz)
 {
 	LIBBPF_OPTS(bpf_prog_load_opts, opts,
 		.log_buf = log_buf,
 		.log_size = log_buf_sz,
 		.log_level = log_buf ? 1 : 0,
+		.fd_array = fd_array,
 	);
 	int fd, err, exp_err = 0;
 	const char *exp_msg = NULL;
@@ -214,7 +215,7 @@ int libbpf_probe_bpf_prog_type(enum bpf_prog_type prog_type, const void *opts)
 	if (opts)
 		return libbpf_err(-EINVAL);
 
-	ret = probe_prog_load(prog_type, insns, insn_cnt, NULL, 0);
+	ret = probe_prog_load(prog_type, insns, insn_cnt, NULL, NULL, 0);
 	return libbpf_err(ret);
 }
 
@@ -448,7 +449,7 @@ int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helpe
 		return -EOPNOTSUPP;
 
 	buf[0] = '\0';
-	ret = probe_prog_load(prog_type, insns, insn_cnt, buf, sizeof(buf));
+	ret = probe_prog_load(prog_type, insns, insn_cnt, NULL, buf, sizeof(buf));
 	if (ret < 0)
 		return libbpf_err(ret);
 
-- 
2.43.0

[PATCH bpf-next v6 3/4] libbpf: Add libbpf_probe_bpf_kfunc API

[Tao Chen]

Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
used to test the availability of the different eBPF kfuncs on the
current system.

Cc: Tao Chen <dylane.chen@didiglobal.com>
Signed-off-by: Tao Chen <chen.dylane@gmail.com>
---
 tools/lib/bpf/libbpf.h        | 19 +++++++++++++-
 tools/lib/bpf/libbpf.map      |  1 +
 tools/lib/bpf/libbpf_probes.c | 48 +++++++++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a..e796e38cf255 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1680,7 +1680,24 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void
  */
 LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
 				       enum bpf_func_id helper_id, const void *opts);
-
+/**
+ * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the
+ * use of a given BPF kfunc from specified BPF program type.
+ * @param prog_type BPF program type used to check the support of BPF kfunc
+ * @param kfunc_id The btf ID of BPF kfunc to check support for
+ * @param btf_fd The module BTF FD, if kfunc is defined in kernel module,
+ * btf_fd is used to point to module's BTF, which is >= 0, and -1 means kfunc
+ * defined in vmlinux.
+ * @param opts reserved for future extensibility, should be NULL
+ * @return 1, if given combination of program type and kfunc is supported; 0,
+ * if the combination is not supported; negative error code if feature
+ * detection for provided input arguments failed or can't be performed
+ *
+ * Make sure the process has required set of CAP_* permissions (or runs as
+ * root) when performing feature checking.
+ */
+LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type,
+				      int kfunc_id, int btf_fd, const void *opts);
 /**
  * @brief **libbpf_num_possible_cpus()** is a helper function to get the
  * number of possible CPUs that the host kernel supports and expects.
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index b5a838de6f47..3bbfe13aeb6a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -438,4 +438,5 @@ LIBBPF_1.6.0 {
 		bpf_linker__new_fd;
 		btf__add_decl_attr;
 		btf__add_type_attr;
+		libbpf_probe_bpf_kfunc;
 } LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index 8ed92ea922b3..ab5591c385de 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
 	return true;
 }
 
+int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
+			   const void *opts)
+{
+	struct bpf_insn insns[] = {
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id),
+		BPF_EXIT_INSN(),
+	};
+	const size_t insn_cnt = ARRAY_SIZE(insns);
+	char buf[4096];
+	int fd_array[2] = {-1};
+	int ret;
+
+	if (opts)
+		return libbpf_err(-EINVAL);
+
+	if (!can_probe_prog_type(prog_type))
+		return -EOPNOTSUPP;
+
+	if (btf_fd >= 0) {
+		fd_array[1] = btf_fd;
+	} else if (btf_fd == -1) {
+		/* insn.off = 0, means vmlinux btf */
+		insns[0].off = 0;
+	} else {
+		return libbpf_err(-EINVAL);
+	}
+
+	buf[0] = '\0';
+	ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
+			      buf, sizeof(buf));
+	if (ret < 0)
+		return libbpf_err(ret);
+
+	/* If BPF verifier recognizes BPF kfunc but it's not supported for
+	 * given BPF program type, it will emit "calling kernel function
+	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
+	 * it will emit "kernel btf_id 4294967295 is not a function". If btf fd
+	 * invalid in module btf, it will emit "invalid module BTF fd specified" or
+	 * "negative offset disallowed for kernel module function call"
+	 */
+	if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
+			(strstr(buf, "invalid module BTF fd")) ||
+			(strstr(buf, "negative offset disallowed"))))
+		return 0;
+
+	return 1; /* assume supported */
+}
+
 int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
 			    const void *opts)
 {
-- 
2.43.0

[PATCH bpf-next v6 4/4] selftests/bpf: Add libbpf_probe_bpf_kfunc API selftests

[Tao Chen]

Add selftests for prog_kfunc feature probing.

 ./test_progs -t libbpf_probe_kfuncs
 #153     libbpf_probe_kfuncs:OK
 Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Tao Chen <chen.dylane@gmail.com>
---
 .../selftests/bpf/prog_tests/libbpf_probes.c  | 111 ++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/libbpf_probes.c b/tools/testing/selftests/bpf/prog_tests/libbpf_probes.c
index 4ed46ed58a7b..96352fb657e5 100644
--- a/tools/testing/selftests/bpf/prog_tests/libbpf_probes.c
+++ b/tools/testing/selftests/bpf/prog_tests/libbpf_probes.c
@@ -126,3 +126,114 @@ void test_libbpf_probe_helpers(void)
 		ASSERT_EQ(res, d->supported, buf);
 	}
 }
+
+static int module_btf_fd(char *module)
+{
+	int fd, err;
+	__u32 id = 0, len;
+	struct bpf_btf_info info;
+	char name[64];
+
+	while (true) {
+		err = bpf_btf_get_next_id(id, &id);
+		if (err)
+			return -1;
+
+		fd = bpf_btf_get_fd_by_id(id);
+		if (fd < 0) {
+			if (errno == ENOENT)
+				continue;
+			return -1;
+		}
+		len = sizeof(info);
+		memset(&info, 0, sizeof(info));
+		info.name = ptr_to_u64(name);
+		info.name_len = sizeof(name);
+		err = bpf_btf_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			close(fd);
+			return -1;
+		}
+		/* find target module btf */
+		if (!strcmp(name, module))
+			break;
+
+		close(fd);
+	}
+
+	return fd;
+}
+
+void test_libbpf_probe_kfuncs(void)
+{
+	int ret, kfunc_id, fd;
+	char *kfunc = "bpf_cpumask_create";
+	struct btf *vmlinux_btf = NULL;
+	struct btf *module_btf = NULL;
+
+	vmlinux_btf = btf__parse("/sys/kernel/btf/vmlinux", NULL);
+	if (!ASSERT_OK_PTR(vmlinux_btf, "btf_parse"))
+		return;
+
+	kfunc_id = btf__find_by_name_kind(vmlinux_btf, kfunc, BTF_KIND_FUNC);
+	if (!ASSERT_GT(kfunc_id, 0, kfunc))
+		goto cleanup;
+
+	/* prog BPF_PROG_TYPE_SYSCALL supports kfunc bpf_cpumask_create */
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_SYSCALL, kfunc_id, -1, NULL);
+	if (!ASSERT_EQ(ret, 1, "kfunc in vmlinux support"))
+		goto cleanup;
+
+	/* prog BPF_PROG_TYPE_KPROBE does not support kfunc bpf_cpumask_create */
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_KPROBE, kfunc_id, -1, NULL);
+	if (!ASSERT_EQ(ret, 0, "kfunc in vmlinux not suuport"))
+		goto cleanup;
+
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_KPROBE, -1, -1, NULL);
+	if (!ASSERT_EQ(ret, 0, "invalid kfunc id:-1"))
+		goto cleanup;
+
+	ret = libbpf_probe_bpf_kfunc(100000, kfunc_id, -1, NULL);
+	if (!ASSERT_ERR(ret, "invalid prog type:100000"))
+		goto cleanup;
+
+	if (!env.has_testmod)
+		goto cleanup;
+
+	module_btf = btf__load_module_btf("bpf_testmod", vmlinux_btf);
+	if (!ASSERT_OK_PTR(module_btf, "load module BTF"))
+		goto cleanup;
+
+	kfunc_id = btf__find_by_name(module_btf, "bpf_kfunc_call_test1");
+	if (!ASSERT_GT(kfunc_id, 0, "func not found"))
+		goto cleanup;
+
+	fd = module_btf_fd("bpf_testmod");
+	if (!ASSERT_GE(fd, 0, "module btf fd"))
+		goto cleanup;
+
+	/* prog BPF_PROG_TYPE_SYSCALL supports kfunc bpf_kfunc_call_test1 in bpf_testmod */
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_SYSCALL, kfunc_id, fd, NULL);
+	if (!ASSERT_EQ(ret, 1, "kfunc in module btf support"))
+		goto cleanup_fd;
+
+	/* prog BPF_PROG_TYPE_KPROBE does not support kfunc bpf_kfunc_call_test1
+	 * in bpf_testmod
+	 */
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_KPROBE, kfunc_id, fd, NULL);
+	if (!ASSERT_EQ(ret, 0, "kfunc in module btf not support"))
+		goto cleanup_fd;
+
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_SYSCALL, -1, fd, NULL);
+	if (!ASSERT_EQ(ret, 0, "invalid kfunc id in module btf"))
+		goto cleanup_fd;
+
+	ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_SYSCALL, kfunc_id, 100, NULL);
+	ASSERT_EQ(ret, 0, "invalid btf fd in module btf");
+
+cleanup_fd:
+	close(fd);
+cleanup:
+	btf__free(vmlinux_btf);
+	btf__free(module_btf);
+}
-- 
2.43.0

Re: [PATCH bpf-next v6 3/4] libbpf: Add libbpf_probe_bpf_kfunc API

[Jiri Olsa]

On Tue, Feb 11, 2025 at 07:18:58PM +0800, Tao Chen wrote:

SNIP

> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index 8ed92ea922b3..ab5591c385de 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
>  	return true;
>  }
>  
> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
> +			   const void *opts)
> +{
> +	struct bpf_insn insns[] = {
> +		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id),
> +		BPF_EXIT_INSN(),
> +	};
> +	const size_t insn_cnt = ARRAY_SIZE(insns);
> +	char buf[4096];
> +	int fd_array[2] = {-1};
> +	int ret;
> +
> +	if (opts)
> +		return libbpf_err(-EINVAL);
> +
> +	if (!can_probe_prog_type(prog_type))
> +		return -EOPNOTSUPP;

we could use libbpf_err(-EOPNOTSUPP) in here and in libbpf_probe_bpf_helper
sry for not spoting it earlier

other than that the patchset looks good to me

Reviewed-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> +
> +	if (btf_fd >= 0) {
> +		fd_array[1] = btf_fd;
> +	} else if (btf_fd == -1) {
> +		/* insn.off = 0, means vmlinux btf */
> +		insns[0].off = 0;
> +	} else {
> +		return libbpf_err(-EINVAL);
> +	}
> +
> +	buf[0] = '\0';
> +	ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
> +			      buf, sizeof(buf));
> +	if (ret < 0)
> +		return libbpf_err(ret);
> +
> +	/* If BPF verifier recognizes BPF kfunc but it's not supported for
> +	 * given BPF program type, it will emit "calling kernel function
> +	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
> +	 * it will emit "kernel btf_id 4294967295 is not a function". If btf fd
> +	 * invalid in module btf, it will emit "invalid module BTF fd specified" or
> +	 * "negative offset disallowed for kernel module function call"
> +	 */
> +	if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
> +			(strstr(buf, "invalid module BTF fd")) ||
> +			(strstr(buf, "negative offset disallowed"))))
> +		return 0;
> +
> +	return 1; /* assume supported */
> +}
> +
>  int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>  			    const void *opts)
>  {
> -- 
> 2.43.0
> 

Re: [PATCH bpf-next v6 3/4] libbpf: Add libbpf_probe_bpf_kfunc API

[Tao Chen]

在 2025/2/11 22:36, Jiri Olsa 写道:
> On Tue, Feb 11, 2025 at 07:18:58PM +0800, Tao Chen wrote:
> 
> SNIP
> 
>> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
>> index 8ed92ea922b3..ab5591c385de 100644
>> --- a/tools/lib/bpf/libbpf_probes.c
>> +++ b/tools/lib/bpf/libbpf_probes.c
>> @@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
>>   	return true;
>>   }
>>   
>> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
>> +			   const void *opts)
>> +{
>> +	struct bpf_insn insns[] = {
>> +		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id),
>> +		BPF_EXIT_INSN(),
>> +	};
>> +	const size_t insn_cnt = ARRAY_SIZE(insns);
>> +	char buf[4096];
>> +	int fd_array[2] = {-1};
>> +	int ret;
>> +
>> +	if (opts)
>> +		return libbpf_err(-EINVAL);
>> +
>> +	if (!can_probe_prog_type(prog_type))
>> +		return -EOPNOTSUPP;
> 
> we could use libbpf_err(-EOPNOTSUPP) in here and in libbpf_probe_bpf_helper
> sry for not spoting it earlier
> 
> other than that the patchset looks good to me
> 
> Reviewed-by: Jiri Olsa <jolsa@kernel.org>
> 
> thanks,
> jirka
> 

Ack. will change it. Thanks for your review!

>> +
>> +	if (btf_fd >= 0) {
>> +		fd_array[1] = btf_fd;
>> +	} else if (btf_fd == -1) {
>> +		/* insn.off = 0, means vmlinux btf */
>> +		insns[0].off = 0;
>> +	} else {
>> +		return libbpf_err(-EINVAL);
>> +	}
>> +
>> +	buf[0] = '\0';
>> +	ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
>> +			      buf, sizeof(buf));
>> +	if (ret < 0)
>> +		return libbpf_err(ret);
>> +
>> +	/* If BPF verifier recognizes BPF kfunc but it's not supported for
>> +	 * given BPF program type, it will emit "calling kernel function
>> +	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
>> +	 * it will emit "kernel btf_id 4294967295 is not a function". If btf fd
>> +	 * invalid in module btf, it will emit "invalid module BTF fd specified" or
>> +	 * "negative offset disallowed for kernel module function call"
>> +	 */
>> +	if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
>> +			(strstr(buf, "invalid module BTF fd")) ||
>> +			(strstr(buf, "negative offset disallowed"))))
>> +		return 0;
>> +
>> +	return 1; /* assume supported */
>> +}
>> +
>>   int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>>   			    const void *opts)
>>   {
>> -- 
>> 2.43.0
>>


-- 
Best Regards
Dylane Chen

Re: [PATCH bpf-next v6 3/4] libbpf: Add libbpf_probe_bpf_kfunc API

[Andrii Nakryiko]

On Tue, Feb 11, 2025 at 3:19 AM Tao Chen <chen.dylane@gmail.com> wrote:
>
> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
> used to test the availability of the different eBPF kfuncs on the
> current system.
>
> Cc: Tao Chen <dylane.chen@didiglobal.com>
> Signed-off-by: Tao Chen <chen.dylane@gmail.com>
> ---
>  tools/lib/bpf/libbpf.h        | 19 +++++++++++++-
>  tools/lib/bpf/libbpf.map      |  1 +
>  tools/lib/bpf/libbpf_probes.c | 48 +++++++++++++++++++++++++++++++++++
>  3 files changed, 67 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 3020ee45303a..e796e38cf255 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1680,7 +1680,24 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void
>   */
>  LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
>                                        enum bpf_func_id helper_id, const void *opts);
> -
> +/**
> + * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the
> + * use of a given BPF kfunc from specified BPF program type.
> + * @param prog_type BPF program type used to check the support of BPF kfunc
> + * @param kfunc_id The btf ID of BPF kfunc to check support for
> + * @param btf_fd The module BTF FD, if kfunc is defined in kernel module,
> + * btf_fd is used to point to module's BTF, which is >= 0, and -1 means kfunc
> + * defined in vmlinux.
> + * @param opts reserved for future extensibility, should be NULL
> + * @return 1, if given combination of program type and kfunc is supported; 0,
> + * if the combination is not supported; negative error code if feature
> + * detection for provided input arguments failed or can't be performed
> + *
> + * Make sure the process has required set of CAP_* permissions (or runs as
> + * root) when performing feature checking.
> + */
> +LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type,
> +                                     int kfunc_id, int btf_fd, const void *opts);
>  /**
>   * @brief **libbpf_num_possible_cpus()** is a helper function to get the
>   * number of possible CPUs that the host kernel supports and expects.
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index b5a838de6f47..3bbfe13aeb6a 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -438,4 +438,5 @@ LIBBPF_1.6.0 {
>                 bpf_linker__new_fd;
>                 btf__add_decl_attr;
>                 btf__add_type_attr;
> +               libbpf_probe_bpf_kfunc;
>  } LIBBPF_1.5.0;
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index 8ed92ea922b3..ab5591c385de 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
>         return true;
>  }
>
> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
> +                          const void *opts)
> +{
> +       struct bpf_insn insns[] = {
> +               BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id),
> +               BPF_EXIT_INSN(),
> +       };
> +       const size_t insn_cnt = ARRAY_SIZE(insns);
> +       char buf[4096];
> +       int fd_array[2] = {-1};
> +       int ret;
> +
> +       if (opts)
> +               return libbpf_err(-EINVAL);
> +
> +       if (!can_probe_prog_type(prog_type))
> +               return -EOPNOTSUPP;

libbpf_err() here

pw-bot: cr

> +
> +       if (btf_fd >= 0) {
> +               fd_array[1] = btf_fd;
> +       } else if (btf_fd == -1) {

let's not hard-code the equality, use < 0 (though I'd follow
verifier's offset == 0 convention for vmlinux BTF here as well to stay
conceptually consistent)

> +               /* insn.off = 0, means vmlinux btf */
> +               insns[0].off = 0;
> +       } else {
> +               return libbpf_err(-EINVAL);
> +       }
> +
> +       buf[0] = '\0';
> +       ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
> +                             buf, sizeof(buf));
> +       if (ret < 0)
> +               return libbpf_err(ret);
> +
> +       /* If BPF verifier recognizes BPF kfunc but it's not supported for
> +        * given BPF program type, it will emit "calling kernel function
> +        * bpf_cpumask_create is not allowed", if the kfunc id is invalid,

bpf_cpumask_create -> <name> to keep comments generic?

> +        * it will emit "kernel btf_id 4294967295 is not a function". If btf fd

same as above, use <id> placeholder instead of specific number?

and keep BTF (all caps) use consistent, please

> +        * invalid in module btf, it will emit "invalid module BTF fd specified" or

ditto, btf -> BTF

> +        * "negative offset disallowed for kernel module function call"
> +        */
> +       if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
> +                       (strstr(buf, "invalid module BTF fd")) ||
> +                       (strstr(buf, "negative offset disallowed"))))

stylistically, given amount of checks, I'd probably go with the
following structure

if (ret > 0)
    return 1;

if (strstr(buf, "not allowed") ||
    strstr(buf, "not a function") ||
...)
    return 0;

> +               return 0;
> +
> +       return 1; /* assume supported */
> +}
> +
>  int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>                             const void *opts)
>  {
> --
> 2.43.0
>

Re: [PATCH bpf-next v6 3/4] libbpf: Add libbpf_probe_bpf_kfunc API

[Tao Chen]

在 2025/2/12 06:24, Andrii Nakryiko 写道:
> On Tue, Feb 11, 2025 at 3:19 AM Tao Chen <chen.dylane@gmail.com> wrote:
>>
>> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
>> used to test the availability of the different eBPF kfuncs on the
>> current system.
>>
>> Cc: Tao Chen <dylane.chen@didiglobal.com>
>> Signed-off-by: Tao Chen <chen.dylane@gmail.com>
>> ---
>>   tools/lib/bpf/libbpf.h        | 19 +++++++++++++-
>>   tools/lib/bpf/libbpf.map      |  1 +
>>   tools/lib/bpf/libbpf_probes.c | 48 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 67 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>> index 3020ee45303a..e796e38cf255 100644
>> --- a/tools/lib/bpf/libbpf.h
>> +++ b/tools/lib/bpf/libbpf.h
>> @@ -1680,7 +1680,24 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void
>>    */
>>   LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
>>                                         enum bpf_func_id helper_id, const void *opts);
>> -
>> +/**
>> + * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the
>> + * use of a given BPF kfunc from specified BPF program type.
>> + * @param prog_type BPF program type used to check the support of BPF kfunc
>> + * @param kfunc_id The btf ID of BPF kfunc to check support for
>> + * @param btf_fd The module BTF FD, if kfunc is defined in kernel module,
>> + * btf_fd is used to point to module's BTF, which is >= 0, and -1 means kfunc
>> + * defined in vmlinux.
>> + * @param opts reserved for future extensibility, should be NULL
>> + * @return 1, if given combination of program type and kfunc is supported; 0,
>> + * if the combination is not supported; negative error code if feature
>> + * detection for provided input arguments failed or can't be performed
>> + *
>> + * Make sure the process has required set of CAP_* permissions (or runs as
>> + * root) when performing feature checking.
>> + */
>> +LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type,
>> +                                     int kfunc_id, int btf_fd, const void *opts);
>>   /**
>>    * @brief **libbpf_num_possible_cpus()** is a helper function to get the
>>    * number of possible CPUs that the host kernel supports and expects.
>> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
>> index b5a838de6f47..3bbfe13aeb6a 100644
>> --- a/tools/lib/bpf/libbpf.map
>> +++ b/tools/lib/bpf/libbpf.map
>> @@ -438,4 +438,5 @@ LIBBPF_1.6.0 {
>>                  bpf_linker__new_fd;
>>                  btf__add_decl_attr;
>>                  btf__add_type_attr;
>> +               libbpf_probe_bpf_kfunc;
>>   } LIBBPF_1.5.0;
>> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
>> index 8ed92ea922b3..ab5591c385de 100644
>> --- a/tools/lib/bpf/libbpf_probes.c
>> +++ b/tools/lib/bpf/libbpf_probes.c
>> @@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type)
>>          return true;
>>   }
>>
>> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd,
>> +                          const void *opts)
>> +{
>> +       struct bpf_insn insns[] = {
>> +               BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id),
>> +               BPF_EXIT_INSN(),
>> +       };
>> +       const size_t insn_cnt = ARRAY_SIZE(insns);
>> +       char buf[4096];
>> +       int fd_array[2] = {-1};
>> +       int ret;
>> +
>> +       if (opts)
>> +               return libbpf_err(-EINVAL);
>> +
>> +       if (!can_probe_prog_type(prog_type))
>> +               return -EOPNOTSUPP;
> 
> libbpf_err() here
> 
> pw-bot: cr
> 

Ack.

>> +
>> +       if (btf_fd >= 0) {
>> +               fd_array[1] = btf_fd;
>> +       } else if (btf_fd == -1) {
> 
> let's not hard-code the equality, use < 0 (though I'd follow
> verifier's offset == 0 convention for vmlinux BTF here as well to stay
> conceptually consistent)
> 

Ack.

>> +               /* insn.off = 0, means vmlinux btf */
>> +               insns[0].off = 0;
>> +       } else {
>> +               return libbpf_err(-EINVAL);
>> +       }
>> +
>> +       buf[0] = '\0';
>> +       ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
>> +                             buf, sizeof(buf));
>> +       if (ret < 0)
>> +               return libbpf_err(ret);
>> +
>> +       /* If BPF verifier recognizes BPF kfunc but it's not supported for
>> +        * given BPF program type, it will emit "calling kernel function
>> +        * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
> 
> bpf_cpumask_create -> <name> to keep comments generic?
> 
>> +        * it will emit "kernel btf_id 4294967295 is not a function". If btf fd
> 
> same as above, use <id> placeholder instead of specific number?
> 
> and keep BTF (all caps) use consistent, please

Ack.

> 
>> +        * invalid in module btf, it will emit "invalid module BTF fd specified" or
> 
> ditto, btf -> BTF
> 
>> +        * "negative offset disallowed for kernel module function call"
>> +        */
>> +       if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
>> +                       (strstr(buf, "invalid module BTF fd")) ||
>> +                       (strstr(buf, "negative offset disallowed"))))
> 
> stylistically, given amount of checks, I'd probably go with the
> following structure

Ack. will change it.

> 
> if (ret > 0)
>      return 1;
> 
> if (strstr(buf, "not allowed") ||
>      strstr(buf, "not a function") ||
> ...)
>      return 0;
> 
>> +               return 0;
>> +
>> +       return 1; /* assume supported */
>> +}
>> +
>>   int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>>                              const void *opts)
>>   {
>> --
>> 2.43.0
>>


-- 
Best Regards
Dylane Chen