[PATCH RFC 4/5] selftests/bpf: Add file_build_id test

Jiri Olsa
2023-02-01T13:58:38Z

The test attaches bpf program to sched_process_exec tracepoint
and gets build of executed file from bprm->file object.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
.../selftests/bpf/prog_tests/file_build_id.c | 70 +++++++++++++++++++
.../selftests/bpf/progs/file_build_id.c | 34 +++++++++
tools/testing/selftests/bpf/trace_helpers.c | 35 ++++++++++
tools/testing/selftests/bpf/trace_helpers.h | 1 +
4 files changed, 140 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/file_build_id.c
create mode 100644 tools/testing/selftests/bpf/progs/file_build_id.c

diff --git a/tools/testing/selftests/bpf/prog_tests/file_build_id.c b/tools/testing/selftests/bpf/prog_tests/file_build_id.c
new file mode 100644
index 000000000000..a7b6307cc0f7
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/file_build_id.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <unistd.h>
+#include <test_progs.h>
+#include "file_build_id.skel.h"
+#include "trace_helpers.h"
+
+#define BUILDID_STR_SIZE (BPF_BUILD_ID_SIZE*2 + 1)
+
+void test_file_build_id(void)
+{
+ int go[2], err, child_pid, child_status, c = 1, i;
+ char bpf_build_id[BUILDID_STR_SIZE] = {};
+ struct file_build_id *skel;
+ char *bid = NULL;
+
+ skel = file_build_id__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "file_build_id__open_and_load"))
+ return;
+
+ if (!ASSERT_OK(pipe(go), "pipe"))
+ goto out;
+
+ child_pid = fork();
+ if (child_pid < 0)
+ goto out;
+
+ /* child */
+ if (child_pid == 0) {
+ /* wait for parent's pid update */
+ err = read(go[0], &c, 1);
+ if (!ASSERT_EQ(err, 1, "child_read_pipe"))
+ exit(err);
+
+ execle("/bin/bash", "bash", "-c", "exit 0", NULL, NULL);
+ exit(errno);
+ }
+
+ /* parent, update child's pid and kick it */
+ skel->bss->pid = child_pid;
+
+ err = file_build_id__attach(skel);
+ if (!ASSERT_OK(err, "file_build_id__attach"))
+ goto out;
+
+ err = write(go[1], &c, 1);
+ if (!ASSERT_EQ(err, 1, "child_write_pipe"))
+ goto out;
+
+ /* wait for child to exit */
+ waitpid(child_pid, &child_status, 0);
+ if (!ASSERT_EQ(WEXITSTATUS(child_status), 0, "child_exit_value"))
+ goto out;
+
+ if (!ASSERT_OK(read_buildid("/bin/bash", &bid), "read_buildid"))
+ goto out;
+
+ ASSERT_EQ(skel->bss->build_id_size, strlen(bid)/2, "build_id_size");
+
+ /* Convert bpf build id to string, so we can compare it later. */
+ for (i = 0; i < skel->bss->build_id_size; i++) {
+ sprintf(bpf_build_id + i*2, "%02x",
+ (unsigned char) skel->bss->build_id[i]);
+ }
+ ASSERT_STREQ(bpf_build_id, bid, "build_id_data");
+
+out:
+ file_build_id__destroy(skel);
+ free(bid);
+}
diff --git a/tools/testing/selftests/bpf/progs/file_build_id.c b/tools/testing/selftests/bpf/progs/file_build_id.c
new file mode 100644
index 000000000000..639a7217a927
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/file_build_id.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <linux/string.h>
+
+char _license[] SEC("license") = "GPL";
+
+int pid;
+u32 build_id_size;
+char build_id[20];
+
+SEC("tp_btf/sched_process_exec")
+int BPF_PROG(prog, struct task_struct *p, pid_t old_pid, struct linux_binprm *bprm)
+{
+ int cur_pid = bpf_get_current_pid_tgid() >> 32;
+ struct build_id *bid;
+
+ if (pid != cur_pid)
+ return 0;
+
+ if (!bprm->file || !bprm->file->f_bid)
+ return 0;
+
+ bid = bprm->file->f_bid;
+ build_id_size = bid->sz;
+
+ if (build_id_size > 20)
+ return 0;
+
+ memcpy(build_id, bid->data, 20);
+ return 0;
+}
diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 09a16a77bae4..f5557890e383 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -9,6 +9,7 @@
#include <poll.h>
#include <unistd.h>
#include <linux/perf_event.h>
+#include <linux/limits.h>
#include <sys/mman.h>
#include "trace_helpers.h"

@@ -230,3 +231,37 @@ ssize_t get_rel_offset(uintptr_t addr)
fclose(f);
return -EINVAL;
}
+
+int read_buildid(const char *path, char **build_id)
+{
+ char tmp[] = "/tmp/dataXXXXXX";
+ char buf[PATH_MAX + 200];
+ int err, fd;
+ FILE *f;
+
+ fd = mkstemp(tmp);
+ if (fd == -1)
+ return -1;
+ close(fd);
+
+ snprintf(buf, sizeof(buf),
+ "readelf -n %s 2>/dev/null | grep 'Build ID' | awk '{print $3}' > %s",
+ path, tmp);
+
+ err = system(buf);
+ if (err)
+ goto out;
+
+ f = fopen(tmp, "r");
+ if (f) {
+ if (fscanf(f, "%ms$*\n", build_id) != 1) {
+ *build_id = NULL;
+ err = -1;
+ }
+ fclose(f);
+ }
+
+out:
+ unlink(tmp);
+ return err;
+}
diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
index 53efde0e2998..1a38c808b6c2 100644
--- a/tools/testing/selftests/bpf/trace_helpers.h
+++ b/tools/testing/selftests/bpf/trace_helpers.h
@@ -23,4 +23,5 @@ void read_trace_pipe(void);
ssize_t get_uprobe_offset(const void *addr);
ssize_t get_rel_offset(uintptr_t addr);

+int read_buildid(const char *path, char **build_id);
#endif
--
2.39.1