[PATCH v2 bpf-next 3/7] libbpf: add kprobe/uprobe attach API

Andrii Nakryiko
2019-06-21T04:56:14Z

Add ability to attach to kernel and user probes and retprobes.
Implementation depends on perf event support for kprobes/uprobes.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
tools/lib/bpf/libbpf.c | 207 +++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 8 ++
tools/lib/bpf/libbpf.map | 2 +
3 files changed, 217 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2bb1fa008be3..d506772df350 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3969,6 +3969,213 @@ int bpf_program__attach_perf_event(struct bpf_program *prog, int pfd)
return 0;
}

+static int parse_uint(const char *buf)
+{
+ int ret;
+
+ errno = 0;
+ ret = (int)strtol(buf, NULL, 10);
+ if (errno) {
+ ret = -errno;
+ pr_debug("failed to parse '%s' as unsigned int\n", buf);
+ return ret;
+ }
+ if (ret < 0) {
+ pr_debug("failed to parse '%s' as unsigned int\n", buf);
+ return -EINVAL;
+ }
+ return ret;
+}
+
+static int parse_uint_from_file(const char* file)
+{
+ char buf[STRERR_BUFSIZE];
+ int fd, ret;
+
+ fd = open(file, O_RDONLY);
+ if (fd < 0) {
+ ret = -errno;
+ pr_debug("failed to open '%s': %s\n", file,
+ libbpf_strerror_r(ret, buf, sizeof(buf)));
+ return ret;
+ }
+ ret = read(fd, buf, sizeof(buf));
+ ret = ret < 0 ? -errno : ret;
+ close(fd);
+ if (ret < 0) {
+ pr_debug("failed to read '%s': %s\n", file,
+ libbpf_strerror_r(ret, buf, sizeof(buf)));
+ return ret;
+ }
+ if (ret == 0 || ret >= sizeof(buf)) {
+ buf[sizeof(buf) - 1] = 0;
+ pr_debug("unexpected input from '%s': '%s'\n", file, buf);
+ return -EINVAL;
+ }
+ return parse_uint(buf);
+}
+
+static int determine_kprobe_perf_type(void)
+{
+ const char *file = "/sys/bus/event_source/devices/kprobe/type";
+ return parse_uint_from_file(file);
+}
+
+static int determine_uprobe_perf_type(void)
+{
+ const char *file = "/sys/bus/event_source/devices/uprobe/type";
+ return parse_uint_from_file(file);
+}
+
+static int parse_config_from_file(const char *file)
+{
+ char buf[STRERR_BUFSIZE];
+ int fd, ret;
+
+ fd = open(file, O_RDONLY);
+ if (fd < 0) {
+ ret = -errno;
+ pr_debug("failed to open '%s': %s\n", file,
+ libbpf_strerror_r(ret, buf, sizeof(buf)));
+ return ret;
+ }
+ ret = read(fd, buf, sizeof(buf));
+ ret = ret < 0 ? -errno : ret;
+ close(fd);
+ if (ret < 0) {
+ pr_debug("failed to read '%s': %s\n", file,
+ libbpf_strerror_r(ret, buf, sizeof(buf)));
+ return ret;
+ }
+ if (ret == 0 || ret >= sizeof(buf)) {
+ buf[sizeof(buf) - 1] = 0;
+ pr_debug("unexpected input from '%s': '%s'\n", file, buf);
+ return -EINVAL;
+ }
+ if (strncmp(buf, "config:", 7)) {
+ pr_debug("expected 'config:' prefix, found '%s'\n", buf);
+ return -EINVAL;
+ }
+ return parse_uint(buf + 7);
+}
+
+static int determine_kprobe_retprobe_bit(void)
+{
+ const char *file = "/sys/bus/event_source/devices/kprobe/format/retprobe";
+ return parse_config_from_file(file);
+}
+
+static int determine_uprobe_retprobe_bit(void)
+{
+ const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
+ return parse_config_from_file(file);
+}
+
+static int perf_event_open_probe(bool uprobe, bool retprobe, const char* name,
+ uint64_t offset, int pid)
+{
+ struct perf_event_attr attr = {};
+ char errmsg[STRERR_BUFSIZE];
+ int type, pfd, err;
+
+ type = uprobe ? determine_uprobe_perf_type()
+ : determine_kprobe_perf_type();
+ if (type < 0) {
+ pr_warning("failed to determine %s perf type: %s\n",
+ uprobe ? "uprobe" : "kprobe",
+ libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
+ return type;
+ }
+ if (retprobe) {
+ int bit = uprobe ? determine_uprobe_retprobe_bit()
+ : determine_kprobe_retprobe_bit();
+
+ if (bit < 0) {
+ pr_warning("failed to determine %s retprobe bit: %s\n",
+ uprobe ? "uprobe" : "kprobe",
+ libbpf_strerror_r(bit, errmsg,
+ sizeof(errmsg)));
+ return bit;
+ }
+ attr.config |= 1 << bit;
+ }
+ attr.size = sizeof(attr);
+ attr.type = type;
+ attr.config1 = (uint64_t)(void *)name; /* kprobe_func or uprobe_path */
+ attr.config2 = offset; /* kprobe_addr or probe_offset */
+
+ /* pid filter is meaningful only for uprobes */
+ pfd = syscall(__NR_perf_event_open, &attr,
+ pid < 0 ? -1 : pid /* pid */,
+ pid == -1 ? 0 : -1 /* cpu */,
+ -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
+ if (pfd < 0) {
+ err = -errno;
+ pr_warning("%s perf_event_open() failed: %s\n",
+ uprobe ? "uprobe" : "kprobe",
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ return pfd;
+}
+
+int bpf_program__attach_kprobe(struct bpf_program *prog, bool retprobe,
+ const char *func_name)
+{
+ char errmsg[STRERR_BUFSIZE];
+ int pfd, err;
+
+ pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
+ 0 /* offset */, -1 /* pid */);
+ if (pfd < 0) {
+ pr_warning("program '%s': failed to create %s '%s' perf event: %s\n",
+ bpf_program__title(prog, false),
+ retprobe ? "kretprobe" : "kprobe", func_name,
+ libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+ return pfd;
+ }
+ err = bpf_program__attach_perf_event(prog, pfd);
+ if (err) {
+ libbpf_perf_event_disable_and_close(pfd);
+ pr_warning("program '%s': failed to attach to %s '%s': %s\n",
+ bpf_program__title(prog, false),
+ retprobe ? "kretprobe" : "kprobe", func_name,
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ return pfd;
+}
+
+int bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
+ pid_t pid, const char *binary_path,
+ size_t func_offset)
+{
+ char errmsg[STRERR_BUFSIZE];
+ int pfd, err;
+
+ pfd = perf_event_open_probe(true /* uprobe */, retprobe,
+ binary_path, func_offset, pid);
+ if (pfd < 0) {
+ pr_warning("program '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
+ bpf_program__title(prog, false),
+ retprobe ? "uretprobe" : "uprobe",
+ binary_path, func_offset,
+ libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+ return pfd;
+ }
+ err = bpf_program__attach_perf_event(prog, pfd);
+ if (err) {
+ libbpf_perf_event_disable_and_close(pfd);
+ pr_warning("program '%s': failed to attach to %s '%s:0x%zx': %s\n",
+ bpf_program__title(prog, false),
+ retprobe ? "uretprobe" : "uprobe",
+ binary_path, func_offset,
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ return pfd;
+}
+
enum bpf_perf_event_ret
bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
void **copy_mem, size_t *copy_size,
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 76db1bbc0dac..a7264f06aa5f 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -168,6 +168,14 @@ LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
LIBBPF_API int libbpf_perf_event_disable_and_close(int pfd);
LIBBPF_API int bpf_program__attach_perf_event(struct bpf_program *prog,
int pfd);
+LIBBPF_API int bpf_program__attach_kprobe(struct bpf_program *prog,
+ bool retprobe,
+ const char *func_name);
+LIBBPF_API int bpf_program__attach_uprobe(struct bpf_program *prog,
+ bool retprobe,
+ pid_t pid,
+ const char *binary_path,
+ size_t func_offset);

struct bpf_insn;

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d27406982b5a..1a982c2e1751 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -172,7 +172,9 @@ LIBBPF_0.0.4 {
btf_dump__new;
btf__parse_elf;
bpf_object__load_xattr;
+ bpf_program__attach_kprobe;
bpf_program__attach_perf_event;
+ bpf_program__attach_uprobe;
libbpf_num_possible_cpus;
libbpf_perf_event_disable_and_close;
} LIBBPF_0.0.3;
--
2.17.1