libbpf: Add unique_match option for multi kprobe

Jordan reported an issue in Meta production environment where func
try_to_wake_up() is renamed to try_to_wake_up.llvm.<hash>() by clang
compiler at lto mode. The original 'kprobe/try_to_wake_up' does not
work any more since try_to_wake_up() does not match the actual func
name in /proc/kallsyms.

There are a couple of ways to resolve this issue. For example, in
attach_kprobe(), we could do lookup in /proc/kallsyms so try_to_wake_up()
can be replaced by try_to_wake_up.llvm.<hach>(). Or we can force users
to use bpf_program__attach_kprobe() where they need to lookup
/proc/kallsyms to find out try_to_wake_up.llvm.<hach>(). But these two
approaches requires extra work by either libbpf or user.

Luckily, suggested by Andrii, multi kprobe already supports wildcard ('*')
for symbol matching. In the above example, 'try_to_wake_up*' can match
to try_to_wake_up() or try_to_wake_up.llvm.<hash>() and this allows
bpf prog works for different kernels as some kernels may have
try_to_wake_up() and some others may have try_to_wake_up.llvm.<hash>().

The original intention is to kprobe try_to_wake_up() only, so an optional
field unique_match is added to struct bpf_kprobe_multi_opts. If the
field is set to true, the number of matched functions must be one.
Otherwise, the attachment will fail. In the above case, multi kprobe
with 'try_to_wake_up*' and unique_match preserves user functionality.

Reported-by: Jordan Rome <linux@jordanrome.com>
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250109174023.3368432-1-yonghong.song@linux.dev

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 46492cc0927d9455fea89c33cf9f2f9f7bc8f9fd..6c262d0152f81083273d7df5a08da459a0929a00 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11534,7 +11534,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
        struct bpf_link *link = NULL;
        const unsigned long *addrs;
        int err, link_fd, prog_fd;
-       bool retprobe, session;
+       bool retprobe, session, unique_match;
        const __u64 *cookies;
        const char **syms;
        size_t cnt;
@@ -11553,6 +11553,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
        addrs   = OPTS_GET(opts, addrs, false);
        cnt     = OPTS_GET(opts, cnt, false);
        cookies = OPTS_GET(opts, cookies, false);
+       unique_match = OPTS_GET(opts, unique_match, false);
 
        if (!pattern && !addrs && !syms)
                return libbpf_err_ptr(-EINVAL);
@@ -11560,6 +11561,8 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
                return libbpf_err_ptr(-EINVAL);
        if (!pattern && !cnt)
                return libbpf_err_ptr(-EINVAL);
+       if (!pattern && unique_match)
+               return libbpf_err_ptr(-EINVAL);
        if (addrs && syms)
                return libbpf_err_ptr(-EINVAL);
 
@@ -11570,6 +11573,14 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
                        err = libbpf_available_kallsyms_parse(&res);
                if (err)
                        goto error;
+
+               if (unique_match && res.cnt != 1) {
+                       pr_warn("prog '%s': failed to find a unique match for '%s' (%zu matches)\n",
+                               prog->name, pattern, res.cnt);
+                       err = -EINVAL;
+                       goto error;
+               }
+
                addrs = res.addrs;
                cnt = res.cnt;
        }

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d45807103565e670085603dc5c7d9135a7e9031f..3020ee45303a0b876eed06e4ebf809f2f21b6498 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -552,10 +552,12 @@ struct bpf_kprobe_multi_opts {
        bool retprobe;
        /* create session kprobes */
        bool session;
+       /* enforce unique match */
+       bool unique_match;
        size_t :0;
 };
 
-#define bpf_kprobe_multi_opts__last_field session
+#define bpf_kprobe_multi_opts__last_field unique_match
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,