[PATCH 2/2] tracing/kprobe: Add kprobe_event= boot parameter

Masami Hiramatsu
2019-05-21T07:56:45Z

Add kprobe_event= boot parameter to define kprobe events
at boot time.
The definition syntax is similar to tracefs/kprobe_events
interface, but use ',' and ';' instead of ' ' and '\n'
respectively. e.g.

kprobe_event=p,vfs_read,$arg1,$arg2

This puts a probe on vfs_read with argument1 and 2, and
enable the new event.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 13 ++++++
Documentation/trace/kprobetrace.rst | 14 ++++++
kernel/trace/trace_kprobe.c | 54 +++++++++++++++++++++++
3 files changed, 81 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..96b22db7f763 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2002,6 +2002,19 @@
Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
the default is off.

+ kprobe_event=[probe-list]
+ [FTRACE] Add kprobe events and enable at boot time.
+ The probe-list is a semicolon delimited list of probe
+ definitions. Each definition is same as kprobe_events
+ interface, but the parameters are comma delimited.
+ For example, to add a kprobe event on vfs_read with
+ arg1 and arg2, add to the command line;
+
+ kprobe_event=p,vfs_read,$arg1,$arg2
+
+ See also Documentation/trace/kprobetrace.rst "Kernel
+ Boot Parameter" section.
+
kpti= [ARM64] Control page table isolation of user
and kernel address spaces.
Default: enabled on cores which need mitigation.
diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index 235ce2ab131a..5b129215ba33 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -124,6 +124,20 @@ You can check the total number of probe hits and probe miss-hits via
The first column is event name, the second is the number of probe hits,
the third is the number of probe miss-hits.

+Kernel Boot Parameter
+---------------------
+You can add and enable new kprobe events when booting up the kernel by
+"kprobe_event=" parameter. The parameter accepts a semicolon-delimited
+kprobe events, which format is similar to the kprobe_events.
+The difference is that the probe definition parameters are comma-delimited
+instead of space. For example, adding myprobe event on do_sys_open like below
+
+ p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)
+
+should be below for kernel boot parameter (just replace spaces with comma)
+
+ p:myprobe,do_sys_open,dfd=%ax,filename=%dx,flags=%cx,mode=+4($stack)
+

Usage examples
--------------
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 7d736248a070..6983435ff017 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -12,6 +12,8 @@
#include <linux/rculist.h>
#include <linux/error-injection.h>

+#include <asm/setup.h> /* for COMMAND_LINE_SIZE */
+
#include "trace_dynevent.h"
#include "trace_kprobe_selftest.h"
#include "trace_probe.h"
@@ -19,6 +21,17 @@

#define KPROBE_EVENT_SYSTEM "kprobes"
#define KRETPROBE_MAXACTIVE_MAX 4096
+#define MAX_KPROBE_CMDLINE_SIZE 1024
+
+/* Kprobe early definition from command line */
+static char kprobe_boot_events_buf[COMMAND_LINE_SIZE] __initdata;
+
+static int __init set_kprobe_boot_events(char *str)
+{
+ strlcpy(kprobe_boot_events_buf, str, COMMAND_LINE_SIZE);
+ return 0;
+}
+__setup("kprobe_event=", set_kprobe_boot_events);

static int trace_kprobe_create(int argc, const char **argv);
static int trace_kprobe_show(struct seq_file *m, struct dyn_event *ev);
@@ -1450,6 +1463,44 @@ void destroy_local_trace_kprobe(struct trace_event_call *event_call)
}
#endif /* CONFIG_PERF_EVENTS */

+static __init void enable_boot_kprobe_events(void)
+{
+ struct trace_array *tr = top_trace_array();
+ struct trace_event_file *file;
+ struct trace_kprobe *tk;
+ struct dyn_event *pos;
+
+ mutex_lock(&event_mutex);
+ for_each_trace_kprobe(tk, pos) {
+ list_for_each_entry(file, &tr->events, list)
+ if (file->event_call == &tk->tp.call)
+ trace_event_enable_disable(file, 1, 0);
+ }
+ mutex_unlock(&event_mutex);
+}
+
+static __init void setup_boot_kprobe_events(void)
+{
+ char *p, *cmd = kprobe_boot_events_buf;
+ int ret;
+
+ strreplace(kprobe_boot_events_buf, ',', ' ');
+
+ while (cmd && *cmd != '\0') {
+ p = strchr(cmd, ';');
+ if (p)
+ *p++ = '\0';
+
+ ret = trace_run_command(cmd, create_or_delete_trace_kprobe);
+ if (ret)
+ pr_warn("Failed to add event(%d): %s\n", ret, cmd);
+
+ cmd = p;
+ }
+
+ enable_boot_kprobe_events();
+}
+
/* Make a tracefs interface for controlling probe points */
static __init int init_kprobe_trace(void)
{
@@ -1481,6 +1532,9 @@ static __init int init_kprobe_trace(void)

if (!entry)
pr_warn("Could not create tracefs 'kprobe_profile' entry\n");
+
+ setup_boot_kprobe_events();
+
return 0;
}
fs_initcall(init_kprobe_trace);