[PATCH 6/8] libbpf: Add bpf_program__attach_kprobe_opts for multi kprobes

Jiri Olsa
2022-02-02T13:54:21Z

Adding support to bpf_program__attach_kprobe_opts to load kprobes
to multiple functions.

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

Adding also support to use '*' wildcard in 'kprobe/kretprobe' section
name by SEC macro, like:

SEC("kprobe/bpf_fentry_test*")
SEC("kretprobe/bpf_fentry_test*")

This will set kprobe's expected_attach_type to BPF_TRACE_FPROBE,
and attach it to provided functions pattern.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/lib/bpf/libbpf.c | 136 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 133 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7d595cfd03bc..6b343ef77ed8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8607,13 +8607,15 @@ static struct bpf_link *attach_trace(const struct bpf_program *prog, long cookie
static struct bpf_link *attach_lsm(const struct bpf_program *prog, long cookie);
static struct bpf_link *attach_iter(const struct bpf_program *prog, long cookie);

+static int init_kprobe(struct bpf_program *prog, long cookie);
+
static const struct bpf_sec_def section_defs[] = {
SEC_DEF("socket", SOCKET_FILTER, 0, SEC_NONE | SEC_SLOPPY_PFX),
SEC_DEF("sk_reuseport/migrate", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
SEC_DEF("sk_reuseport", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
- SEC_DEF("kprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
+ SEC_DEF("kprobe/", KPROBE, 0, SEC_NONE, attach_kprobe, .init_fn = init_kprobe),
SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE),
- SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
+ SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe, .init_fn = init_kprobe),
SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE),
SEC_DEF("tc", SCHED_CLS, 0, SEC_NONE),
SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE | SEC_SLOPPY_PFX | SEC_DEPRECATED),
@@ -10031,6 +10033,123 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
return pfd;
}

+struct fprobe_resolve {
+ const char *name;
+ __u64 *addrs;
+ __u32 alloc;
+ __u32 cnt;
+};
+
+static bool glob_matches(const char *glob, const char *s)
+{
+ int n = strlen(glob);
+
+ if (n == 1 && glob[0] == '*')
+ return true;
+
+ if (glob[0] == '*' && glob[n - 1] == '*') {
+ const char *subs;
+ /* substring match */
+
+ /* this is hacky, but we don't want to allocate
+ * for no good reason
+ */
+ ((char *)glob)[n - 1] = '\0';
+ subs = strstr(s, glob + 1);
+ ((char *)glob)[n - 1] = '*';
+
+ return subs != NULL;
+ } else if (glob[0] == '*') {
+ size_t nn = strlen(s);
+ /* suffix match */
+
+ /* too short for a given suffix */
+ if (nn < n - 1)
+ return false;
+ return strcmp(s + nn - (n - 1), glob + 1) == 0;
+ } else if (glob[n - 1] == '*') {
+ /* prefix match */
+ return strncmp(s, glob, n - 1) == 0;
+ } else {
+ /* exact match */
+ return strcmp(glob, s) == 0;
+ }
+}
+
+static int resolve_fprobe_cb(void *arg, unsigned long long sym_addr,
+ char sym_type, const char *sym_name)
+{
+ struct fprobe_resolve *res = arg;
+ __u64 *p;
+
+ if (!glob_matches(res->name, sym_name))
+ return 0;
+
+ if (res->cnt == res->alloc) {
+ res->alloc = max((__u32) 16, res->alloc * 3 / 2);
+ p = libbpf_reallocarray(res->addrs, res->alloc, sizeof(__u32));
+ if (!p)
+ return -ENOMEM;
+ res->addrs = p;
+ }
+ res->addrs[res->cnt++] = sym_addr;
+ return 0;
+}
+
+static struct bpf_link *
+attach_fprobe_opts(const struct bpf_program *prog,
+ const char *func_name,
+ const struct bpf_kprobe_opts *kopts)
+{
+ DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
+ struct fprobe_resolve res = {
+ .name = func_name,
+ };
+ struct bpf_link *link = NULL;
+ char errmsg[STRERR_BUFSIZE];
+ int err, link_fd, prog_fd;
+ bool retprobe;
+
+ err = libbpf__kallsyms_parse(&res, resolve_fprobe_cb);
+ if (err)
+ goto error;
+ if (!res.cnt) {
+ err = -ENOENT;
+ goto error;
+ }
+
+ retprobe = OPTS_GET(kopts, retprobe, false);
+
+ opts.fprobe.addrs = (__u64) res.addrs;
+ opts.fprobe.cnt = res.cnt;
+ opts.flags = retprobe ? BPF_F_FPROBE_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_FPROBE, &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,
@@ -10047,6 +10166,9 @@ 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_FPROBE)
+ return attach_fprobe_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);
@@ -10112,6 +10234,14 @@ struct bpf_link *bpf_program__attach_kprobe(const struct bpf_program *prog,
return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
}

+static int init_kprobe(struct bpf_program *prog, long cookie)
+{
+ /* If we have wildcard, switch to fprobe link. */
+ if (strchr(prog->sec_name, '*'))
+ bpf_program__set_expected_attach_type(prog, BPF_TRACE_FPROBE);
+ return 0;
+}
+
static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cookie)
{
DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
@@ -10127,7 +10257,7 @@ static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cooki
else
func_name = prog->sec_name + sizeof("kprobe/") - 1;

- 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);
--
2.34.1