x86: kprobes: add kprobes smoke tests that run on boot

Here is a quick and naive smoke test for kprobes. This is intended to
just verify if some unrelated change broke the *probes subsystem. It is
self contained, architecture agnostic and isn't of any great use by itself.

This needs to be built in the kernel and runs a basic set of tests to
verify if kprobes, jprobes and kretprobes run fine on the kernel. In case
of an error, it'll print out a message with a "BUG" prefix.

This is a start; we intend to add more tests to this bucket over time.

Thanks to Jim Keniston and Masami Hiramatsu for comments and suggestions.

Tested on x86 (32/64) and powerpc.
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/kprobes.h

@@ -182,6 +182,15 @@ static inline void kretprobe_assert(struct kretprobe_instance *ri,
 	}
 }
 
+#ifdef CONFIG_KPROBES_SANITY_TEST
+extern int init_test_probes(void);
+#else
+static inline int init_test_probes(void)
+{
+	return 0;
+}
+#endif /* CONFIG_KPROBES_SANITY_TEST */
+
 extern spinlock_t kretprobe_lock;
 extern struct mutex kprobe_mutex;
 extern int arch_prepare_kprobe(struct kprobe *p);
@@ -227,6 +236,7 @@ void unregister_kretprobe(struct kretprobe *rp);
 
 void kprobe_flush_task(struct task_struct *tk);
 void recycle_rp_inst(struct kretprobe_instance *ri, struct hlist_head *head);
+
 #else /* CONFIG_KPROBES */
 
 #define __kprobes	/**/

kernel/Makefile

@@ -43,6 +43,7 @@ obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
+obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
 obj-$(CONFIG_AUDIT_TREE) += audit_tree.o

kernel/kprobes.c

@@ -824,6 +824,8 @@ static int __init init_kprobes(void)
 	if (!err)
 		err = register_die_notifier(&kprobe_exceptions_nb);
 
+	if (!err)
+		init_test_probes();
 	return err;
 }
 

kernel/test_kprobes.c

+/*
+ * test_kprobes.c - simple sanity test for *probes
+ *
+ * Copyright IBM Corp. 2008
+ *
+ * This program is free software;  you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
+ * the GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/random.h>
+
+#define div_factor 3
+
+static u32 rand1, preh_val, posth_val, jph_val;
+static int errors, handler_errors, num_tests;
+
+static noinline u32 kprobe_target(u32 value)
+{
+	/*
+	 * gcc ignores noinline on some architectures unless we stuff
+	 * sufficient lard into the function. The get_kprobe() here is
+	 * just for that.
+	 *
+	 * NOTE: We aren't concerned about the correctness of get_kprobe()
+	 * here; hence, this call is neither under !preempt nor with the
+	 * kprobe_mutex held. This is fine(tm)
+	 */
+	if (get_kprobe((void *)0xdeadbeef))
+		printk(KERN_INFO "Kprobe smoke test: probe on 0xdeadbeef!\n");
+
+	return (value / div_factor);
+}
+
+static int kp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	preh_val = (rand1 / div_factor);
+	return 0;
+}
+
+static void kp_post_handler(struct kprobe *p, struct pt_regs *regs,
+		unsigned long flags)
+{
+	if (preh_val != (rand1 / div_factor)) {
+		handler_errors++;
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"incorrect value in post_handler\n");
+	}
+	posth_val = preh_val + div_factor;
+}
+
+static struct kprobe kp = {
+	.symbol_name = "kprobe_target",
+	.pre_handler = kp_pre_handler,
+	.post_handler = kp_post_handler
+};
+
+static int test_kprobe(void)
+{
+	int ret;
+
+	ret = register_kprobe(&kp);
+	if (ret < 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"register_kprobe returned %d\n", ret);
+		return ret;
+	}
+
+	ret = kprobe_target(rand1);
+	unregister_kprobe(&kp);
+
+	if (preh_val == 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"kprobe pre_handler not called\n");
+		handler_errors++;
+	}
+
+	if (posth_val == 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"kprobe post_handler not called\n");
+		handler_errors++;
+	}
+
+	return 0;
+}
+
+static u32 j_kprobe_target(u32 value)
+{
+	if (value != rand1) {
+		handler_errors++;
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"incorrect value in jprobe handler\n");
+	}
+
+	jph_val = rand1;
+	jprobe_return();
+	return 0;
+}
+
+static struct jprobe jp = {
+	.entry		= j_kprobe_target,
+	.kp.symbol_name = "kprobe_target"
+};
+
+static int test_jprobe(void)
+{
+	int ret;
+
+	ret = register_jprobe(&jp);
+	if (ret < 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"register_jprobe returned %d\n", ret);
+		return ret;
+	}
+
+	ret = kprobe_target(rand1);
+	unregister_jprobe(&jp);
+	if (jph_val == 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"jprobe handler not called\n");
+		handler_errors++;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_KRETPROBES
+static u32 krph_val;
+
+static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+	unsigned long ret = regs_return_value(regs);
+
+	if (ret != (rand1 / div_factor)) {
+		handler_errors++;
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"incorrect value in kretprobe handler\n");
+	}
+
+	krph_val = (rand1 / div_factor);
+	return 0;
+}
+
+static struct kretprobe rp = {
+	.handler	= return_handler,
+	.kp.symbol_name = "kprobe_target"
+};
+
+static int test_kretprobe(void)
+{
+	int ret;
+
+	ret = register_kretprobe(&rp);
+	if (ret < 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"register_kretprobe returned %d\n", ret);
+		return ret;
+	}
+
+	ret = kprobe_target(rand1);
+	unregister_kretprobe(&rp);
+	if (krph_val == 0) {
+		printk(KERN_ERR "Kprobe smoke test failed: "
+				"kretprobe handler not called\n");
+		handler_errors++;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_KRETPROBES */
+
+int init_test_probes(void)
+{
+	int ret;
+
+	do {
+		rand1 = random32();
+	} while (rand1 <= div_factor);
+
+	printk(KERN_INFO "Kprobe smoke test started\n");
+	num_tests++;
+	ret = test_kprobe();
+	if (ret < 0)
+		errors++;
+
+	num_tests++;
+	ret = test_jprobe();
+	if (ret < 0)
+		errors++;
+
+#ifdef CONFIG_KRETPROBES
+	num_tests++;
+	ret = test_kretprobe();
+	if (ret < 0)
+		errors++;
+#endif /* CONFIG_KRETPROBES */
+
+	if (errors)
+		printk(KERN_ERR "BUG: Kprobe smoke test: %d out of "
+				"%d tests failed\n", errors, num_tests);
+	else if (handler_errors)
+		printk(KERN_ERR "BUG: Kprobe smoke test: %d error(s) "
+				"running handlers\n", handler_errors);
+	else
+		printk(KERN_INFO "Kprobe smoke test passed successfully\n");
+
+	return 0;
+}

lib/Kconfig.debug

@@ -494,6 +494,18 @@ config RCU_TORTURE_TEST
 	  Say M if you want the RCU torture tests to build as a module.
 	  Say N if you are unsure.
 
+config KPROBES_SANITY_TEST
+	bool "Kprobes sanity tests"
+	depends on DEBUG_KERNEL
+	depends on KPROBES
+	default n
+	help
+	  This option provides for testing basic kprobes functionality on
+	  boot. A sample kprobe, jprobe and kretprobe are inserted and
+	  verified for functionality.
+
+	  Say N if you are unsure.
+
 config LKDTM
 	tristate "Linux Kernel Dump Test Tool Module"
 	depends on DEBUG_KERNEL