selftests/bpf: Uprobe tests should verify param/return values

uprobe/uretprobe tests don't do any validation of arguments/return values,
and without this we can't be sure we are attached to the right function,
or that we are indeed attached to a uprobe or uretprobe.  To fix this
record argument and return value for auto-attached functions and ensure
these match expectations.  Also need to filter by pid to ensure we do
not pick up stray malloc()s since auto-attach traces libc system-wide.
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1649245431-29956-4-git-send-email-alan.maguire@oracle.com

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

@@ -5,14 +5,17 @@
 #include "test_uprobe_autoattach.skel.h"
 
 /* uprobe attach point */
-static void autoattach_trigger_func(void)
+static noinline int autoattach_trigger_func(int arg)
 {
 	asm volatile ("");
+	return arg + 1;
 }
 
 void test_uprobe_autoattach(void)
 {
 	struct test_uprobe_autoattach *skel;
+	int trigger_val = 100, trigger_ret;
+	size_t malloc_sz = 1;
 	char *mem;
 
 	skel = test_uprobe_autoattach__open_and_load();
@@ -22,17 +25,25 @@ void test_uprobe_autoattach(void)
 	if (!ASSERT_OK(test_uprobe_autoattach__attach(skel), "skel_attach"))
 		goto cleanup;
 
+	skel->bss->test_pid = getpid();
+
 	/* trigger & validate uprobe & uretprobe */
-	autoattach_trigger_func();
+	trigger_ret = autoattach_trigger_func(trigger_val);
+
+	skel->bss->test_pid = getpid();
 
 	/* trigger & validate shared library u[ret]probes attached by name */
-	mem = malloc(1);
+	mem = malloc(malloc_sz);
 	free(mem);
 
-	ASSERT_EQ(skel->bss->uprobe_byname_res, 1, "check_uprobe_byname_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname_res, 2, "check_uretprobe_byname_res");
-	ASSERT_EQ(skel->bss->uprobe_byname2_res, 3, "check_uprobe_byname2_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname2_res, 4, "check_uretprobe_byname2_res");
+	ASSERT_EQ(skel->bss->uprobe_byname_parm1, trigger_val, "check_uprobe_byname_parm1");
+	ASSERT_EQ(skel->bss->uprobe_byname_ran, 1, "check_uprobe_byname_ran");
+	ASSERT_EQ(skel->bss->uretprobe_byname_rc, trigger_ret, "check_uretprobe_byname_rc");
+	ASSERT_EQ(skel->bss->uretprobe_byname_ran, 2, "check_uretprobe_byname_ran");
+	ASSERT_EQ(skel->bss->uprobe_byname2_parm1, malloc_sz, "check_uprobe_byname2_parm1");
+	ASSERT_EQ(skel->bss->uprobe_byname2_ran, 3, "check_uprobe_byname2_ran");
+	ASSERT_EQ(skel->bss->uretprobe_byname2_rc, mem, "check_uretprobe_byname2_rc");
+	ASSERT_EQ(skel->bss->uretprobe_byname2_ran, 4, "check_uretprobe_byname2_ran");
 cleanup:
 	test_uprobe_autoattach__destroy(skel);
 }

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

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2022, Oracle and/or its affiliates. */
 
-#include <linux/ptrace.h>
-#include <linux/bpf.h>
+#include "vmlinux.h"
+
+#include <bpf/bpf_core_read.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
-int uprobe_byname_res = 0;
-int uretprobe_byname_res = 0;
-int uprobe_byname2_res = 0;
-int uretprobe_byname2_res = 0;
+int uprobe_byname_parm1 = 0;
+int uprobe_byname_ran = 0;
+int uretprobe_byname_rc = 0;
+int uretprobe_byname_ran = 0;
+size_t uprobe_byname2_parm1 = 0;
+int uprobe_byname2_ran = 0;
+char *uretprobe_byname2_rc = NULL;
+int uretprobe_byname2_ran = 0;
+
+int test_pid;
 
 /* This program cannot auto-attach, but that should not stop other
  * programs from attaching.
@@ -23,14 +30,16 @@ int handle_uprobe_noautoattach(struct pt_regs *ctx)
 SEC("uprobe//proc/self/exe:autoattach_trigger_func")
 int handle_uprobe_byname(struct pt_regs *ctx)
 {
-	uprobe_byname_res = 1;
+	uprobe_byname_parm1 = PT_REGS_PARM1_CORE(ctx);
+	uprobe_byname_ran = 1;
 	return 0;
 }
 
 SEC("uretprobe//proc/self/exe:autoattach_trigger_func")
 int handle_uretprobe_byname(struct pt_regs *ctx)
 {
-	uretprobe_byname_res = 2;
+	uretprobe_byname_rc = PT_REGS_RC_CORE(ctx);
+	uretprobe_byname_ran = 2;
 	return 0;
 }
 
@@ -38,14 +47,26 @@ int handle_uretprobe_byname(struct pt_regs *ctx)
 SEC("uprobe/libc.so.6:malloc")
 int handle_uprobe_byname2(struct pt_regs *ctx)
 {
-	uprobe_byname2_res = 3;
+	int pid = bpf_get_current_pid_tgid() >> 32;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid)
+		return 0;
+	uprobe_byname2_parm1 = PT_REGS_PARM1_CORE(ctx);
+	uprobe_byname2_ran = 3;
 	return 0;
 }
 
-SEC("uretprobe/libc.so.6:free")
+SEC("uretprobe/libc.so.6:malloc")
 int handle_uretprobe_byname2(struct pt_regs *ctx)
 {
-	uretprobe_byname2_res = 4;
+	int pid = bpf_get_current_pid_tgid() >> 32;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid)
+		return 0;
+	uretprobe_byname2_rc = (char *)PT_REGS_RC_CORE(ctx);
+	uretprobe_byname2_ran = 4;
 	return 0;
 }