hw-breakpoints: sample HW breakpoint over kernel data address

This patch introduces a sample kernel module to demonstrate the use of Hardware Breakpoint feature. It places a breakpoint over the kernel variable 'pid_max' to monitor all write operations and emits a function-backtrace when done. Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

hw-breakpoints: sample HW breakpoint over kernel data address
This patch introduces a sample kernel module to demonstrate the use of Hardware Breakpoint feature. It places a breakpoint over the kernel variable 'pid_max' to monitor all write operations and emits a function-backtrace when done. Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
K.Prasad · Frederic Weisbecker
1 parent 17f557e5b5
Showing 4 changed files with 92 additions and 1 deletions Side-by-side Diff
samples/Kconfig
samples/Makefile
samples/hw_breakpoint/Makefile
samples/hw_breakpoint/data_breakpoint.c
@@ -45,5 +45,11 @@
 	default m
 	depends on SAMPLE_KPROBES && KRETPROBES
  
+config SAMPLE_HW_BREAKPOINT
+	tristate "Build kernel hardware breakpoint examples -- loadable module only"
+	depends on HAVE_HW_BREAKPOINT && m
+	help
+	  This builds kernel hardware breakpoint example modules.
+
 endif # SAMPLES
 # Makefile for Linux samples code
  
-obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/ trace_events/
+obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/ \
+			trace_events/ hw_breakpoint/
+obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o
+/*
+ * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
+ *
+ * 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 will 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * usage: insmod data_breakpoint.ko ksym=<ksym_name>
+ *
+ * This file is a kernel module that places a breakpoint over ksym_name kernel
+ * variable using Hardware Breakpoint register. The corresponding handler which
+ * prints a backtrace is invoked everytime a write operation is performed on
+ * that variable.
+ *
+ * Copyright (C) IBM Corporation, 2009
+ */
+#include <linux/module.h>	/* Needed by all modules */
+#include <linux/kernel.h>	/* Needed for KERN_INFO */
+#include <linux/init.h>		/* Needed for the macros */
+
+#include <asm/hw_breakpoint.h>
+
+struct hw_breakpoint sample_hbp;
+
+static char ksym_name[KSYM_NAME_LEN] = "pid_max";
+module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
+MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
+			" write operations on the kernel symbol");
+
+void sample_hbp_handler(struct hw_breakpoint *temp, struct pt_regs
+								*temp_regs)
+{
+	printk(KERN_INFO "%s value is changed\n", ksym_name);
+	dump_stack();
+	printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
+}
+
+static int __init hw_break_module_init(void)
+{
+	int ret;
+
+#ifdef CONFIG_X86
+	sample_hbp.info.name = ksym_name;
+	sample_hbp.info.type = HW_BREAKPOINT_WRITE;
+	sample_hbp.info.len = HW_BREAKPOINT_LEN_4;
+#endif /* CONFIG_X86 */
+
+	sample_hbp.triggered = (void *)sample_hbp_handler;
+
+	ret = register_kernel_hw_breakpoint(&sample_hbp);
+
+	if (ret < 0) {
+		printk(KERN_INFO "Breakpoint registration failed\n");
+		return ret;
+	} else
+		printk(KERN_INFO "HW Breakpoint for %s write installed\n",
+								ksym_name);
+
+	return 0;
+}
+
+static void __exit hw_break_module_exit(void)
+{
+	unregister_kernel_hw_breakpoint(&sample_hbp);
+	printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
+}
+
+module_init(hw_break_module_init);
+module_exit(hw_break_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("K.Prasad");
+MODULE_DESCRIPTION("ksym breakpoint");
...	...	@@ -45,5 +45,11 @@
45	45	default m
46	46	depends on SAMPLE_KPROBES && KRETPROBES
47	47
	48	+config SAMPLE_HW_BREAKPOINT
	49	+ tristate "Build kernel hardware breakpoint examples -- loadable module only"
	50	+ depends on HAVE_HW_BREAKPOINT && m
	51	+ help
	52	+ This builds kernel hardware breakpoint example modules.
	53	+
48	54	endif # SAMPLES
1	1	# Makefile for Linux samples code
2	2
3		-obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ trace_events/
	3	+obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ \
	4	+ trace_events/ hw_breakpoint/
	1	+/*
	2	+ * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
	3	+ *
	4	+ * This program is free software; you can redistribute it and/or modify
	5	+ * it under the terms of the GNU General Public License as published by
	6	+ * the Free Software Foundation; either version 2 of the License, or
	7	+ * (at your option) any later version.
	8	+ *
	9	+ * This program is distributed in the hope that it will be useful,
	10	+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	+ * GNU General Public License for more details.
	13	+ *
	14	+ * You should have received a copy of the GNU General Public License
	15	+ * along with this program; if not, write to the Free Software
	16	+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	+ *
	18	+ * usage: insmod data_breakpoint.ko ksym=<ksym_name>
	19	+ *
	20	+ * This file is a kernel module that places a breakpoint over ksym_name kernel
	21	+ * variable using Hardware Breakpoint register. The corresponding handler which
	22	+ * prints a backtrace is invoked everytime a write operation is performed on
	23	+ * that variable.
	24	+ *
	25	+ * Copyright (C) IBM Corporation, 2009
	26	+ */
	27	+#include <linux/module.h> /* Needed by all modules */
	28	+#include <linux/kernel.h> /* Needed for KERN_INFO */
	29	+#include <linux/init.h> /* Needed for the macros */
	30	+
	31	+#include <asm/hw_breakpoint.h>
	32	+
	33	+struct hw_breakpoint sample_hbp;
	34	+
	35	+static char ksym_name[KSYM_NAME_LEN] = "pid_max";
	36	+module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
	37	+MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
	38	+ " write operations on the kernel symbol");
	39	+
	40	+void sample_hbp_handler(struct hw_breakpoint *temp, struct pt_regs
	41	+ *temp_regs)
	42	+{
	43	+ printk(KERN_INFO "%s value is changed\n", ksym_name);
	44	+ dump_stack();
	45	+ printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
	46	+}
	47	+
	48	+static int __init hw_break_module_init(void)
	49	+{
	50	+ int ret;
	51	+
	52	+#ifdef CONFIG_X86
	53	+ sample_hbp.info.name = ksym_name;
	54	+ sample_hbp.info.type = HW_BREAKPOINT_WRITE;
	55	+ sample_hbp.info.len = HW_BREAKPOINT_LEN_4;
	56	+#endif /* CONFIG_X86 */
	57	+
	58	+ sample_hbp.triggered = (void *)sample_hbp_handler;
	59	+
	60	+ ret = register_kernel_hw_breakpoint(&sample_hbp);
	61	+
	62	+ if (ret < 0) {
	63	+ printk(KERN_INFO "Breakpoint registration failed\n");
	64	+ return ret;
	65	+ } else
	66	+ printk(KERN_INFO "HW Breakpoint for %s write installed\n",
	67	+ ksym_name);
	68	+
	69	+ return 0;
	70	+}
	71	+
	72	+static void __exit hw_break_module_exit(void)
	73	+{
	74	+ unregister_kernel_hw_breakpoint(&sample_hbp);
	75	+ printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
	76	+}
	77	+
	78	+module_init(hw_break_module_init);
	79	+module_exit(hw_break_module_exit);
	80	+
	81	+MODULE_LICENSE("GPL");
	82	+MODULE_AUTHOR("K.Prasad");
	83	+MODULE_DESCRIPTION("ksym breakpoint");