diff options
author | Masami Hiramatsu <mhiramat@kernel.org> | 2022-03-15 15:02:00 +0100 |
---|---|---|
committer | Alexei Starovoitov <ast@kernel.org> | 2022-03-18 04:16:58 +0100 |
commit | 6ee64cc3020b5b5537827c71d8eaac814ad4d346 (patch) | |
tree | 361bd8b1ce2bc869da84c12fd912ffae1905b7a8 /samples/fprobe | |
parent | fprobe: Add exit_handler support (diff) | |
download | linux-6ee64cc3020b5b5537827c71d8eaac814ad4d346.tar.xz linux-6ee64cc3020b5b5537827c71d8eaac814ad4d346.zip |
fprobe: Add sample program for fprobe
Add a sample program for the fprobe. The sample_fprobe puts a fprobe on
kernel_clone() by default. This dump stack and some called address info
at the function entry and exit.
The sample_fprobe.ko gets 2 parameters.
- symbol: you can specify the comma separated symbols or wildcard symbol
pattern (in this case you can not use comma)
- stackdump: a bool value to enable or disable stack dump in the fprobe
handler.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/164735291987.1084943.4449670993752806840.stgit@devnote2
Diffstat (limited to 'samples/fprobe')
-rw-r--r-- | samples/fprobe/Makefile | 3 | ||||
-rw-r--r-- | samples/fprobe/fprobe_example.c | 120 |
2 files changed, 123 insertions, 0 deletions
diff --git a/samples/fprobe/Makefile b/samples/fprobe/Makefile new file mode 100644 index 000000000000..ecccbfa6e99b --- /dev/null +++ b/samples/fprobe/Makefile @@ -0,0 +1,3 @@ +# SPDX-License-Identifier: GPL-2.0-only + +obj-$(CONFIG_SAMPLE_FPROBE) += fprobe_example.o diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c new file mode 100644 index 000000000000..24d3cf109140 --- /dev/null +++ b/samples/fprobe/fprobe_example.c @@ -0,0 +1,120 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Here's a sample kernel module showing the use of fprobe to dump a + * stack trace and selected registers when kernel_clone() is called. + * + * For more information on theory of operation of kprobes, see + * Documentation/trace/kprobes.rst + * + * You will see the trace data in /var/log/messages and on the console + * whenever kernel_clone() is invoked to create a new process. + */ + +#define pr_fmt(fmt) "%s: " fmt, __func__ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/fprobe.h> +#include <linux/sched/debug.h> +#include <linux/slab.h> + +#define BACKTRACE_DEPTH 16 +#define MAX_SYMBOL_LEN 4096 +struct fprobe sample_probe; + +static char symbol[MAX_SYMBOL_LEN] = "kernel_clone"; +module_param_string(symbol, symbol, sizeof(symbol), 0644); +static char nosymbol[MAX_SYMBOL_LEN] = ""; +module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644); +static bool stackdump = true; +module_param(stackdump, bool, 0644); + +static void show_backtrace(void) +{ + unsigned long stacks[BACKTRACE_DEPTH]; + unsigned int len; + + len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2); + stack_trace_print(stacks, len, 24); +} + +static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) +{ + pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); + if (stackdump) + show_backtrace(); +} + +static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs) +{ + unsigned long rip = instruction_pointer(regs); + + pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", + (void *)ip, (void *)ip, (void *)rip, (void *)rip); + if (stackdump) + show_backtrace(); +} + +static int __init fprobe_init(void) +{ + char *p, *symbuf = NULL; + const char **syms; + int ret, count, i; + + sample_probe.entry_handler = sample_entry_handler; + sample_probe.exit_handler = sample_exit_handler; + + if (strchr(symbol, '*')) { + /* filter based fprobe */ + ret = register_fprobe(&sample_probe, symbol, + nosymbol[0] == '\0' ? NULL : nosymbol); + goto out; + } else if (!strchr(symbol, ',')) { + symbuf = symbol; + ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1); + goto out; + } + + /* Comma separated symbols */ + symbuf = kstrdup(symbol, GFP_KERNEL); + if (!symbuf) + return -ENOMEM; + p = symbuf; + count = 1; + while ((p = strchr(++p, ',')) != NULL) + count++; + + pr_info("%d symbols found\n", count); + + syms = kcalloc(count, sizeof(char *), GFP_KERNEL); + if (!syms) { + kfree(symbuf); + return -ENOMEM; + } + + p = symbuf; + for (i = 0; i < count; i++) + syms[i] = strsep(&p, ","); + + ret = register_fprobe_syms(&sample_probe, syms, count); + kfree(syms); + kfree(symbuf); +out: + if (ret < 0) + pr_err("register_fprobe failed, returned %d\n", ret); + else + pr_info("Planted fprobe at %s\n", symbol); + + return ret; +} + +static void __exit fprobe_exit(void) +{ + unregister_fprobe(&sample_probe); + + pr_info("fprobe at %s unregistered\n", symbol); +} + +module_init(fprobe_init) +module_exit(fprobe_exit) +MODULE_LICENSE("GPL"); |