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Wed, 12 Feb 2025 07:39:26 -0800 (PST) From: Tao Chen To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, haoluo@google.com, jolsa@kernel.org, qmo@kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, chen.dylane@gmail.com, Tao Chen Subject: [PATCH bpf-next v7 3/4] libbpf: Add libbpf_probe_bpf_kfunc API Date: Wed, 12 Feb 2025 23:39:11 +0800 Message-Id: <20250212153912.24116-4-chen.dylane@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20250212153912.24116-1-chen.dylane@gmail.com> References: <20250212153912.24116-1-chen.dylane@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: X-Patchwork-Delegate: bpf@iogearbox.net 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 Reviewed-by: Jiri Olsa Signed-off-by: Tao Chen --- 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..c79b4475b956 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 < 0 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 de2b1205b436..74928e26b5b9 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 libbpf_err(-EOPNOTSUPP); + + if (btf_fd >= 0) + fd_array[1] = btf_fd; + else + /* insn.off = 0, means vmlinux btf */ + insns[0].off = 0; + + 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 (ret > 0) + return 1; /* assume supported */ + + /* If BPF verifier recognizes BPF kfunc but it's not supported for + * given BPF program type, it will emit "calling kernel function + * is not allowed", if the kfunc id is invalid, + * it will emit "kernel btf_id 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 (strstr(buf, "not allowed") || strstr(buf, "not a function") || + strstr(buf, "invalid module BTF fd") || + strstr(buf, "negative offset disallowed")) + return 0; + + return 1; +} + int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id, const void *opts) {