data_breakpoint.c 2.3 KB

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  1. // SPDX-License-Identifier: GPL-2.0-or-later
  2. /*
  3. * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
  4. *
  5. * usage: insmod data_breakpoint.ko ksym=<ksym_name>
  6. *
  7. * This file is a kernel module that places a breakpoint over ksym_name kernel
  8. * variable using Hardware Breakpoint register. The corresponding handler which
  9. * prints a backtrace is invoked every time a write operation is performed on
  10. * that variable.
  11. *
  12. * Copyright (C) IBM Corporation, 2009
  13. *
  14. * Author: K.Prasad <prasad@linux.vnet.ibm.com>
  15. */
  16. #include <linux/module.h> /* Needed by all modules */
  17. #include <linux/kernel.h> /* Needed for KERN_INFO */
  18. #include <linux/init.h> /* Needed for the macros */
  19. #include <linux/kallsyms.h>
  20. #include <linux/perf_event.h>
  21. #include <linux/hw_breakpoint.h>
  22. struct perf_event * __percpu *sample_hbp;
  23. static char ksym_name[KSYM_NAME_LEN] = "jiffies";
  24. module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
  25. MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
  26. " write operations on the kernel symbol");
  27. static void sample_hbp_handler(struct perf_event *bp,
  28. struct perf_sample_data *data,
  29. struct pt_regs *regs)
  30. {
  31. printk(KERN_INFO "%s value is changed\n", ksym_name);
  32. dump_stack();
  33. printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
  34. }
  35. static int __init hw_break_module_init(void)
  36. {
  37. int ret;
  38. struct perf_event_attr attr;
  39. void *addr = __symbol_get(ksym_name);
  40. if (!addr)
  41. return -ENXIO;
  42. hw_breakpoint_init(&attr);
  43. attr.bp_addr = (unsigned long)addr;
  44. attr.bp_len = HW_BREAKPOINT_LEN_4;
  45. attr.bp_type = HW_BREAKPOINT_W;
  46. sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
  47. if (IS_ERR((void __force *)sample_hbp)) {
  48. ret = PTR_ERR((void __force *)sample_hbp);
  49. goto fail;
  50. }
  51. printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
  52. return 0;
  53. fail:
  54. printk(KERN_INFO "Breakpoint registration failed\n");
  55. return ret;
  56. }
  57. static void __exit hw_break_module_exit(void)
  58. {
  59. unregister_wide_hw_breakpoint(sample_hbp);
  60. symbol_put(ksym_name);
  61. printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
  62. }
  63. module_init(hw_break_module_init);
  64. module_exit(hw_break_module_exit);
  65. MODULE_LICENSE("GPL");
  66. MODULE_AUTHOR("K.Prasad");
  67. MODULE_DESCRIPTION("ksym breakpoint");