[PATCH 2/2] selftests/bpf: Add uretprobe test for return_instance management

[Liao Chang]

This patch add three testcases to verify the proper management of
return_instance data by uretprobes:

- uretprobe_longjmp() verifies that longjmp() bypasses the uretprobe BPF
  program attached to the exit of instrumented function.

- uretprobe_cleanup_return_instance() verifies that uretprobe reclaim
  the return_instances data created before a longjmp(), which leads to
  kernel recount the nested depth of instrumented function.

- uretprobe_reach_nestedness_limit() confirms that the uretprobe doesn't
  reclaim the return_instances data created before longjmp() and hijack
  the return address of instrumented function upon the nestedness depth
  reache the limits (64).

Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
---
 .../bpf/prog_tests/uretprobe_depth.c          | 150 ++++++++++++++++++
 .../selftests/bpf/progs/uretprobe_depth.c     |  19 +++
 2 files changed, 169 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/uretprobe_depth.c
 create mode 100644 tools/testing/selftests/bpf/progs/uretprobe_depth.c

diff --git a/tools/testing/selftests/bpf/prog_tests/uretprobe_depth.c b/tools/testing/selftests/bpf/prog_tests/uretprobe_depth.c
new file mode 100644
index 000000000000..ba03b1868e37
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/uretprobe_depth.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+
+#include <unistd.h>
+#include <setjmp.h>
+#include <asm/ptrace.h>
+#include <linux/compiler.h>
+#include <linux/stringify.h>
+#include "uretprobe_depth.skel.h"
+
+#define RETVAL			0xFFFF
+#define JMPVAL			0x4B1D
+#define MAX_URETPROBE_DEPTH	64 // See include/linux/uprobes.h
+#define NR_OMITTED_URETPROBE	16
+static jmp_buf jmp;
+
+unsigned long __uretprobe_longjmp(int nest, int jmpval, int retval)
+{
+	if (nest) {
+		nest = ++retval < MAX_URETPROBE_DEPTH + NR_OMITTED_URETPROBE;
+		return __uretprobe_longjmp(nest, jmpval, retval);
+	}
+
+	if (jmpval == JMPVAL) {
+		longjmp(jmp, jmpval);
+		return 0;
+	} else
+		return retval;
+}
+
+static void uretprobe_longjmp(void)
+{
+	if (setjmp(jmp) == JMPVAL) {
+		__uretprobe_longjmp(0, 0, JMPVAL);
+		return;
+	}
+
+	__uretprobe_longjmp(0, JMPVAL, RETVAL);
+}
+
+static void uretprobe_cleanup_return_instances(void)
+{
+	if (setjmp(jmp) == JMPVAL) {
+		/*
+		 * Cleanup these return instance data created before longjmp
+		 * firstly. Then create 16 new return_instance data from here.
+		 */
+		__uretprobe_longjmp(1, 0, MAX_URETPROBE_DEPTH);
+		return;
+	}
+
+	/* Create 8 return_instance data from here. */
+	__uretprobe_longjmp(1, JMPVAL,
+			    MAX_URETPROBE_DEPTH + NR_OMITTED_URETPROBE / 2);
+}
+
+static void uretprobe_reach_nestedness_limit(void)
+{
+	if (setjmp(jmp) == JMPVAL) {
+		/*
+		 * Due to uretprobe reach to the nestedness limit, it doesn't
+		 * cleanup the return instance created before longjmp.
+		 */
+		__uretprobe_longjmp(1, 0, MAX_URETPROBE_DEPTH);
+		return;
+	}
+
+	/* Create 64 return_instance from here. */
+	__uretprobe_longjmp(1, JMPVAL, 0);
+}
+
+static void test_uretprobe_longjmp(void)
+{
+	struct uretprobe_depth *skel = NULL;
+	int err;
+
+	skel = uretprobe_depth__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "uretprobe_depth__open_and_load"))
+		goto cleanup;
+
+	err = uretprobe_depth__attach(skel);
+	if (!ASSERT_OK(err, "uretprobe_depth__attach"))
+		goto cleanup;
+
+	skel->bss->retval = -1;
+
+	uretprobe_longjmp();
+
+	ASSERT_EQ(skel->bss->retval, JMPVAL, "return value");
+
+cleanup:
+	uretprobe_depth__destroy(skel);
+}
+
+static void test_uretprobe_reach_nestedness_limit(void)
+{
+	struct uretprobe_depth *skel = NULL;
+	int err;
+
+	skel = uretprobe_depth__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "uretprobe_depth__open_and_load"))
+		goto cleanup;
+
+	err = uretprobe_depth__attach(skel);
+	if (!ASSERT_OK(err, "uretprobe_depth__attach"))
+		goto cleanup;
+
+	skel->bss->depth = 0;
+
+	uretprobe_reach_nestedness_limit();
+
+	ASSERT_EQ(skel->bss->depth, 0, "nest depth");
+
+cleanup:
+	uretprobe_depth__destroy(skel);
+}
+
+static void test_uretprobe_cleanup_return_instances(void)
+{
+	struct uretprobe_depth *skel = NULL;
+	int err;
+
+	skel = uretprobe_depth__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "uretprobe_depth__open_and_load"))
+		goto cleanup;
+
+	err = uretprobe_depth__attach(skel);
+	if (!ASSERT_OK(err, "uretprobe_depth__attach"))
+		goto cleanup;
+
+	skel->bss->depth = 0;
+
+	uretprobe_cleanup_return_instances();
+
+	ASSERT_EQ(skel->bss->depth, NR_OMITTED_URETPROBE + 1, "nest depth");
+
+cleanup:
+	uretprobe_depth__destroy(skel);
+}
+
+void test_uretprobe_return_instance(void)
+{
+	if (test__start_subtest("uretprobe_longjmp"))
+		test_uretprobe_longjmp();
+	if (test__start_subtest("uretprobe_cleanup_return_instances"))
+		test_uretprobe_cleanup_return_instances();
+	if (test__start_subtest("uretprobe_reach_nestedness_limit"))
+		test_uretprobe_reach_nestedness_limit();
+}
diff --git a/tools/testing/selftests/bpf/progs/uretprobe_depth.c b/tools/testing/selftests/bpf/progs/uretprobe_depth.c
new file mode 100644
index 000000000000..b71f2de52b5e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/uretprobe_depth.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <string.h>
+
+int depth;
+unsigned long retval;
+
+char _license[] SEC("license") = "GPL";
+
+SEC("uretprobe//proc/self/exe:__uretprobe_longjmp")
+int uretprobe(struct pt_regs *ctx)
+{
+	depth++;
+#if defined(__TARGET_ARCH_arm64) || defined(__aarch64__)
+	retval = ctx->regs[0];
+#endif
+	return 0;
+}
-- 
2.34.1