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| 2 | |
| 3 | * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
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| 4 | *
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| 5 | * usage: insmod data_breakpoint.ko ksym=<ksym_name>
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| 6 | *
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| 7 | * This file is a kernel module that places a breakpoint over ksym_name kernel
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| 8 | * variable using Hardware Breakpoint register. The corresponding handler which
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| 9 | * prints a backtrace is invoked every time a write operation is performed on
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| 10 | * that variable.
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| 11 | *
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| 12 | * Copyright (C) IBM Corporation, 2009
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| 13 | *
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| 14 | * Author: K.Prasad <[email protected]>
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| 15 |
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| 16 | #include <linux/module.h>
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| 17 | #include <linux/kernel.h>
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| 18 | #include <linux/init.h>
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| 19 | #include <linux/kallsyms.h>
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| 20 |
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| 21 | #include <linux/perf_event.h>
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| 22 | #include <linux/hw_breakpoint.h>
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| 23 |
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| 24 | static struct perf_event * __percpu *sample_hbp;
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| 25 |
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| 26 | static char ksym_name[KSYM_NAME_LEN] = "jiffies";
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| 27 | module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
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| 28 | MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
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| 29 | " write operations on the kernel symbol");
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| 30 |
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| 31 | static void sample_hbp_handler(struct perf_event *bp,
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| 32 | struct perf_sample_data *data,
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| 33 | struct pt_regs *regs)
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| 34 | {
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| 35 | printk(KERN_INFO "%s value is changed\n", ksym_name);
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| 36 | dump_stack();
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| 37 | printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
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| 38 | }
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| 39 |
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| 40 | static int __init hw_break_module_init(void)
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| 41 | {
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| 42 | int ret;
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| 43 | struct perf_event_attr attr;
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| 44 | void *addr = __symbol_get(ksym_name);
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| 45 |
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| 46 | if (!addr)
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| 47 | return -ENXIO;
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| 48 |
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| 49 | hw_breakpoint_init(&attr);
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| 50 | attr.bp_addr = (unsigned long)addr;
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| 51 | attr.bp_len = HW_BREAKPOINT_LEN_4;
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| 52 | attr.bp_type = HW_BREAKPOINT_W;
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| 53 |
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| 54 | sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
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| 55 | if (IS_ERR_PCPU(sample_hbp)) {
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| 56 | ret = PTR_ERR_PCPU(sample_hbp);
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| 57 | goto fail;
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| 58 | }
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| 59 |
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| 60 | printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
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| 61 |
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| 62 | return 0;
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| 63 |
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| 64 | fail:
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| 65 | printk(KERN_INFO "Breakpoint registration failed\n");
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| 66 |
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| 67 | return ret;
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| 68 | }
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| 69 |
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| 70 | static void __exit hw_break_module_exit(void)
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| 71 | {
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| 72 | unregister_wide_hw_breakpoint(sample_hbp);
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| 73 | #ifdef CONFIG_MODULE_UNLOAD
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| 74 | __symbol_put(ksym_name);
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| 75 | #endif
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| 76 | printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
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| 77 | }
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| 78 |
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| 79 | module_init(hw_break_module_init);
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| 80 | module_exit(hw_break_module_exit);
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| 81 |
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| 82 | MODULE_LICENSE("GPL");
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| 83 | MODULE_AUTHOR("K.Prasad");
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| 84 | MODULE_DESCRIPTION("ksym breakpoint");
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