155 lines
4.0 KiB
C
155 lines
4.0 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Here's a sample kernel module showing the use of fprobe to dump a
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* stack trace and selected registers when kernel_clone() is called.
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*
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* For more information on theory of operation of kprobes, see
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* Documentation/trace/kprobes.rst
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*
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* You will see the trace data in /var/log/messages and on the console
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* whenever kernel_clone() is invoked to create a new process.
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*/
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#define pr_fmt(fmt) "%s: " fmt, __func__
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/fprobe.h>
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#include <linux/sched/debug.h>
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#include <linux/slab.h>
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#define BACKTRACE_DEPTH 16
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#define MAX_SYMBOL_LEN 4096
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static struct fprobe sample_probe;
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static unsigned long nhit;
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static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
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module_param_string(symbol, symbol, sizeof(symbol), 0644);
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MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern.");
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static char nosymbol[MAX_SYMBOL_LEN] = "";
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module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
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MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern.");
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static bool stackdump = true;
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module_param(stackdump, bool, 0644);
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MODULE_PARM_DESC(stackdump, "Enable stackdump.");
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static bool use_trace = false;
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module_param(use_trace, bool, 0644);
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MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging.");
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static void show_backtrace(void)
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{
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unsigned long stacks[BACKTRACE_DEPTH];
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unsigned int len;
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len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
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stack_trace_print(stacks, len, 24);
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}
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static int sample_entry_handler(struct fprobe *fp, unsigned long ip,
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unsigned long ret_ip,
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struct pt_regs *regs, void *data)
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{
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if (use_trace)
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/*
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* This is just an example, no kernel code should call
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* trace_printk() except when actively debugging.
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*/
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trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
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else
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pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
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nhit++;
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if (stackdump)
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show_backtrace();
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return 0;
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}
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static void sample_exit_handler(struct fprobe *fp, unsigned long ip,
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unsigned long ret_ip, struct pt_regs *regs,
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void *data)
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{
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unsigned long rip = ret_ip;
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if (use_trace)
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/*
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* This is just an example, no kernel code should call
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* trace_printk() except when actively debugging.
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*/
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trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
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(void *)ip, (void *)ip, (void *)rip, (void *)rip);
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else
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pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
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(void *)ip, (void *)ip, (void *)rip, (void *)rip);
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nhit++;
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if (stackdump)
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show_backtrace();
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}
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static int __init fprobe_init(void)
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{
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char *p, *symbuf = NULL;
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const char **syms;
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int ret, count, i;
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sample_probe.entry_handler = sample_entry_handler;
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sample_probe.exit_handler = sample_exit_handler;
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if (strchr(symbol, '*')) {
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/* filter based fprobe */
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ret = register_fprobe(&sample_probe, symbol,
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nosymbol[0] == '\0' ? NULL : nosymbol);
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goto out;
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} else if (!strchr(symbol, ',')) {
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symbuf = symbol;
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ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
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goto out;
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}
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/* Comma separated symbols */
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symbuf = kstrdup(symbol, GFP_KERNEL);
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if (!symbuf)
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return -ENOMEM;
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p = symbuf;
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count = 1;
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while ((p = strchr(++p, ',')) != NULL)
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count++;
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pr_info("%d symbols found\n", count);
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syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
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if (!syms) {
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kfree(symbuf);
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return -ENOMEM;
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}
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p = symbuf;
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for (i = 0; i < count; i++)
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syms[i] = strsep(&p, ",");
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ret = register_fprobe_syms(&sample_probe, syms, count);
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kfree(syms);
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kfree(symbuf);
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out:
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if (ret < 0)
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pr_err("register_fprobe failed, returned %d\n", ret);
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else
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pr_info("Planted fprobe at %s\n", symbol);
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return ret;
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}
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static void __exit fprobe_exit(void)
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{
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unregister_fprobe(&sample_probe);
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pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
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symbol, nhit, sample_probe.nmissed);
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}
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module_init(fprobe_init)
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module_exit(fprobe_exit)
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MODULE_DESCRIPTION("sample kernel module showing the use of fprobe");
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MODULE_LICENSE("GPL");
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