Messages in this thread Patch in this message | | | Date | Thu, 22 Jan 2009 19:42:59 +0530 | From | "K.Prasad" <> | Subject | [RFC Patch 10/10] Sample HW breakpoint over kernel data address |
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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> --- samples/Kconfig | 6 ++ samples/Makefile | 3 - samples/hw_breakpoint/Makefile | 1 samples/hw_breakpoint/data_breakpoint.c | 81 ++++++++++++++++++++++++++++++++ 4 files changed, 90 insertions(+), 1 deletion(-)
Index: linux-hbkpt-lkml-29-rc2/samples/Kconfig =================================================================== --- linux-hbkpt-lkml-29-rc2.orig/samples/Kconfig +++ linux-hbkpt-lkml-29-rc2/samples/Kconfig @@ -39,5 +39,11 @@ config SAMPLE_KRETPROBES default m depends on SAMPLE_KPROBES && KRETPROBES +config SAMPLE_HW_BREAKPOINT + tristate "Build kernel hardware breakpoint examples -- loadable modules only" + depends on m + help + This builds kernel hardware breakpoint example modules. + endif # SAMPLES Index: linux-hbkpt-lkml-29-rc2/samples/Makefile =================================================================== --- linux-hbkpt-lkml-29-rc2.orig/samples/Makefile +++ linux-hbkpt-lkml-29-rc2/samples/Makefile @@ -1,3 +1,4 @@ # Makefile for Linux samples code -obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ +obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ \ + hw_breakpoint/ Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile =================================================================== --- /dev/null +++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile @@ -0,0 +1 @@ +obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c =================================================================== --- /dev/null +++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c @@ -0,0 +1,81 @@ +/* + * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address + * + * This file is a kernel module that places a breakpoint over 'pid_max' kernel + * variable using Hardware Breakpoint register. The corresponding handler which + * prints a backtrace is invoked everytime a write operation is performed on + * that variable. + * + * After inserting this module, invoke a write operation using + * 'echo <desired_value> > /proc/sys/kernel/pid_max' + * to find the function-call backtrace. + * + * 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 pid_max_hw_breakpoint; + +void pid_max_hw_breakpoint_installed(struct hw_breakpoint *temp, struct pt_regs + *temp_regs) +{ + printk(KERN_INFO "pid_max_hw_breakpoint ENABLED\n"); +} + +void pid_max_hw_breakpoint_uninstalled(struct hw_breakpoint *temp, struct + pt_regs *temp_regs) +{ + printk(KERN_INFO "pid_max_hw_breakpoint DISABLED\n"); +} + +void pid_max_hw_breakpoint_handler(struct hw_breakpoint *temp, struct pt_regs + *temp_regs) +{ + printk(KERN_INFO "pid_max value is changed\n"); + dump_stack(); + printk(KERN_INFO "Dump stack from pid_max_hw_breakpoint_handler\n"); +} + +static int __init hw_break_module_init(void) +{ + int ret; + +#ifdef CONFIG_X86 + pid_max_hw_breakpoint.info.name = "pid_max"; + pid_max_hw_breakpoint.info.type = HW_BREAKPOINT_WRITE; + pid_max_hw_breakpoint.info.len = HW_BREAKPOINT_LEN_4; + pid_max_hw_breakpoint.priority = HW_BREAKPOINT_PRIO_NORMAL; + + pid_max_hw_breakpoint.installed = (void*)pid_max_hw_breakpoint_installed; + pid_max_hw_breakpoint.uninstalled = (void*)pid_max_hw_breakpoint_uninstalled; + pid_max_hw_breakpoint.triggered = (void*)pid_max_hw_breakpoint_handler; +#endif /* CONFIG_X86 */ + + ret = register_kernel_hw_breakpoint(&pid_max_hw_breakpoint); + + if (ret < 0) { + printk(KERN_INFO "Breakpoint registration failed\n"); + return ret; + } + else + printk(KERN_INFO "HW Breakpoint for pid_max write installed\n"); + + return 0; +} + +static void __exit hw_break_module_exit(void) +{ + unregister_kernel_hw_breakpoint(&pid_max_hw_breakpoint); + printk(KERN_INFO "HW Breakpoint for pid_max write uninstalled\n"); +} + +module_init(hw_break_module_init); +module_exit(hw_break_module_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("K.Prasad"); +MODULE_DESCRIPTION("pid_max breakpoint");
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