selftests/bpf: Add uretprobe syscall call from user space test

Adding test to verify that when called from outside of the
trampoline provided by kernel, the uretprobe syscall will cause
calling process to receive SIGILL signal and the attached bpf
program is not executed.

Link: https://lore.kernel.org/all/[e-mail]/

Acked-by: Andrii Nakryiko <[e-mail]>
Reviewed-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>

tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c

···
 #include <unistd.h>
 #include <asm/ptrace.h>
 #include <linux/compiler.h>
+#include <linux/stringify.h>
+#include <sys/wait.h>
 #include "uprobe_syscall.skel.h"
+#include "uprobe_syscall_executed.skel.h"
 
 __naked unsigned long uretprobe_regs_trigger(void)
 {
···
 	}
 }
 
+#ifndef __NR_uretprobe
+#define __NR_uretprobe 463
+#endif
+
+__naked unsigned long uretprobe_syscall_call_1(void)
+{
+	/*
+	 * Pretend we are uretprobe trampoline to trigger the return
+	 * probe invocation in order to verify we get SIGILL.
+	 */
+	asm volatile (
+		"pushq %rax\n"
+		"pushq %rcx\n"
+		"pushq %r11\n"
+		"movq $" __stringify(__NR_uretprobe) ", %rax\n"
+		"syscall\n"
+		"popq %r11\n"
+		"popq %rcx\n"
+		"retq\n"
+	);
+}
+
+__naked unsigned long uretprobe_syscall_call(void)
+{
+	asm volatile (
+		"call uretprobe_syscall_call_1\n"
+		"retq\n"
+	);
+}
+
+static void test_uretprobe_syscall_call(void)
+{
+	LIBBPF_OPTS(bpf_uprobe_multi_opts, opts,
+		.retprobe = true,
+	);
+	struct uprobe_syscall_executed *skel;
+	int pid, status, err, go[2], c;
+
+	if (ASSERT_OK(pipe(go), "pipe"))
+		return;
+
+	skel = uprobe_syscall_executed__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "uprobe_syscall_executed__open_and_load"))
+		goto cleanup;
+
+	pid = fork();
+	if (!ASSERT_GE(pid, 0, "fork"))
+		goto cleanup;
+
+	/* child */
+	if (pid == 0) {
+		close(go[1]);
+
+		/* wait for parent's kick */
+		err = read(go[0], &c, 1);
+		if (err != 1)
+			exit(-1);
+
+		uretprobe_syscall_call();
+		_exit(0);
+	}
+
+	skel->links.test = bpf_program__attach_uprobe_multi(skel->progs.test, pid,
+							    "/proc/self/exe",
+							    "uretprobe_syscall_call", &opts);
+	if (!ASSERT_OK_PTR(skel->links.test, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
+	/* kick the child */
+	write(go[1], &c, 1);
+	err = waitpid(pid, &status, 0);
+	ASSERT_EQ(err, pid, "waitpid");
+
+	/* verify the child got killed with SIGILL */
+	ASSERT_EQ(WIFSIGNALED(status), 1, "WIFSIGNALED");
+	ASSERT_EQ(WTERMSIG(status), SIGILL, "WTERMSIG");
+
+	/* verify the uretprobe program wasn't called */
+	ASSERT_EQ(skel->bss->executed, 0, "executed");
+
+cleanup:
+	uprobe_syscall_executed__destroy(skel);
+	close(go[1]);
+	close(go[0]);
+}
 #else
 static void test_uretprobe_regs_equal(void)
 {
···
 }
 
 static void test_uretprobe_regs_change(void)
+{
+	test__skip();
+}
+
+static void test_uretprobe_syscall_call(void)
 {
 	test__skip();
 }
···
 		test_uretprobe_regs_equal();
 	if (test__start_subtest("uretprobe_regs_change"))
 		test_uretprobe_regs_change();
+	if (test__start_subtest("uretprobe_syscall_call"))
+		test_uretprobe_syscall_call();
 }

tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c

···
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <string.h>
+
+struct pt_regs regs;
+
+char _license[] SEC("license") = "GPL";
+
+int executed = 0;
+
+SEC("uretprobe.multi")
+int test(struct pt_regs *regs)
+{
+	executed = 1;
+	return 0;
+}