[PATCH 08/10] libbpf: Add bpf_program__attach_kprobe_opts support for multi kprobes

Jiri Olsa
2022-02-22T17:08:11Z

Adding support to bpf_program__attach_kprobe_opts to attach kprobes
to multiple functions.

If the kprobe program has BPF_TRACE_KPROBE_MULTI as expected_attach_type
it will use the new kprobe_multi link to attach the program. In this case
it will use 'func_name' as pattern for functions to attach.

Adding also new section types 'kprobe.multi' and kretprobe.multi'
that allows to specify wildcards (*?) for functions, like:

SEC("kprobe.multi/bpf_fentry_test*")
SEC("kretprobe.multi/bpf_fentry_test?")

This will set kprobe's expected_attach_type to BPF_TRACE_KPROBE_MULTI,
and attach it to functions provided by the function pattern.

Using glob_match from selftests/bpf/test_progs.c and adding support to
match '?' based on original perf code.

Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Yucong Sun <fallentree@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/lib/bpf/libbpf.c | 130 +++++++++++++++++++++++++++++++++++++++--
1 file changed, 125 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fb530b004a0d..9bee2d70b99d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8622,6 +8622,8 @@ static const struct bpf_sec_def section_defs[] = {
SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE),
SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE),
+ SEC_DEF("kprobe.multi/", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe),
+ SEC_DEF("kretprobe.multi/", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe),
SEC_DEF("tc", SCHED_CLS, 0, SEC_NONE),
SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE | SEC_SLOPPY_PFX | SEC_DEPRECATED),
SEC_DEF("action", SCHED_ACT, 0, SEC_NONE | SEC_SLOPPY_PFX),
@@ -10038,6 +10040,113 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
return pfd;
}

+/* Adapted from perf/util/string.c */
+static bool glob_match(const char *str, const char *pat)
+{
+ while (*str && *pat && *pat != '*') {
+ if (*pat == '?') { /* Matches any single character */
+ str++;
+ pat++;
+ continue;
+ }
+ if (*str != *pat)
+ return false;
+ str++;
+ pat++;
+ }
+ /* Check wild card */
+ if (*pat == '*') {
+ while (*pat == '*')
+ pat++;
+ if (!*pat) /* Tail wild card matches all */
+ return true;
+ while (*str)
+ if (glob_match(str++, pat))
+ return true;
+ }
+ return !*str && !*pat;
+}
+
+struct kprobe_multi_resolve {
+ const char *name;
+ __u64 *addrs;
+ size_t cap;
+ size_t cnt;
+};
+
+static int
+resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
+ const char *sym_name, void *ctx)
+{
+ struct kprobe_multi_resolve *res = ctx;
+ int err;
+
+ if (!glob_match(sym_name, res->name))
+ return 0;
+
+ err = libbpf_ensure_mem((void **)&res->addrs, &res->cap, sizeof(__u64),
+ res->cnt + 1);
+ if (err)
+ return err;
+
+ res->addrs[res->cnt++] = sym_addr;
+ return 0;
+}
+
+static struct bpf_link *
+attach_kprobe_multi_opts(const struct bpf_program *prog,
+ const char *func_pattern,
+ const struct bpf_kprobe_opts *kopts)
+{
+ DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
+ struct kprobe_multi_resolve res = {
+ .name = func_pattern,
+ };
+ struct bpf_link *link = NULL;
+ char errmsg[STRERR_BUFSIZE];
+ int err, link_fd, prog_fd;
+ bool retprobe;
+
+ err = libbpf_kallsyms_parse(resolve_kprobe_multi_cb, &res);
+ if (err)
+ goto error;
+ if (!res.cnt) {
+ err = -ENOENT;
+ goto error;
+ }
+
+ retprobe = OPTS_GET(kopts, retprobe, false);
+
+ opts.kprobe_multi.addrs = ptr_to_u64(res.addrs);
+ opts.kprobe_multi.cnt = res.cnt;
+ opts.flags = retprobe ? BPF_F_KPROBE_MULTI_RETURN : 0;
+
+ link = calloc(1, sizeof(*link));
+ if (!link) {
+ err = -ENOMEM;
+ goto error;
+ }
+ link->detach = &bpf_link__detach_fd;
+
+ prog_fd = bpf_program__fd(prog);
+ link_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_KPROBE_MULTI, &opts);
+ if (link_fd < 0) {
+ err = -errno;
+ pr_warn("prog '%s': failed to attach to %s: %s\n",
+ prog->name, res.name,
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ goto error;
+ }
+ link->fd = link_fd;
+ free(res.addrs);
+ return link;
+
+error:
+ free(link);
+ free(res.addrs);
+ return libbpf_err_ptr(err);
+}
+
struct bpf_link *
bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
const char *func_name,
@@ -10054,6 +10163,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
if (!OPTS_VALID(opts, bpf_kprobe_opts))
return libbpf_err_ptr(-EINVAL);

+ if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI)
+ return attach_kprobe_multi_opts(prog, func_name, opts);
+
retprobe = OPTS_GET(opts, retprobe, false);
offset = OPTS_GET(opts, offset, 0);
pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
@@ -10122,19 +10234,27 @@ struct bpf_link *bpf_program__attach_kprobe(const struct bpf_program *prog,
static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cookie)
{
DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
+ const char *func_name = NULL;
unsigned long offset = 0;
struct bpf_link *link;
- const char *func_name;
char *func;
int n, err;

- opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe/");
- if (opts.retprobe)
+ opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe");
+
+ if (str_has_pfx(prog->sec_name, "kretprobe/"))
func_name = prog->sec_name + sizeof("kretprobe/") - 1;
- else
+ else if (str_has_pfx(prog->sec_name, "kprobe/"))
func_name = prog->sec_name + sizeof("kprobe/") - 1;
+ else if (str_has_pfx(prog->sec_name, "kretprobe.multi/"))
+ func_name = prog->sec_name + sizeof("kretprobe.multi/") - 1;
+ else if (str_has_pfx(prog->sec_name, "kprobe.multi/"))
+ func_name = prog->sec_name + sizeof("kprobe.multi/") - 1;
+
+ if (!func_name)
+ return libbpf_err_ptr(-EINVAL);

- n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
+ n = sscanf(func_name, "%m[a-zA-Z0-9_.*?]+%li", &func, &offset);
if (n < 1) {
err = -EINVAL;
pr_warn("kprobe name is invalid: %s\n", func_name);
--
2.35.1