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Subject[PATCH -mm] kprobes: kretprobe user entry-handler (updated)
This is a repost of a patch which was reviewed earlier at:
http://lkml.org/lkml/2007/11/13/58 (thanks to Jim Keniston and Srinivasa for their review comments). This provides support to add an optional user defined callback to be run at function entry of a kretprobe'd function. It also modifies the kprobe smoke tests to include an entry-handler during the kretprobe sanity test.

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
---
diff -upNr -X /home/guest/patches/dontdiff.txt linux-2.6.24-rc8-mm1/Documentation/kprobes.txt linux-2.6.24-rc8-mm1_kp/Documentation/kprobes.txt
--- linux-2.6.24-rc8-mm1/Documentation/kprobes.txt 2008-01-16 09:52:48.000000000 +0530
+++ linux-2.6.24-rc8-mm1_kp/Documentation/kprobes.txt 2008-01-26 17:12:43.000000000 +0530
@@ -96,7 +96,9 @@ or in registers (e.g., for x86_64 or for
The jprobe will work in either case, so long as the handler's
prototype matches that of the probed function.

-1.3 How Does a Return Probe Work?
+1.3 Return Probes
+
+1.3.1 How Does a Return Probe Work?

When you call register_kretprobe(), Kprobes establishes a kprobe at
the entry to the function. When the probed function is called and this
@@ -107,9 +109,9 @@ At boot time, Kprobes registers a kprobe

When the probed function executes its return instruction, control
passes to the trampoline and that probe is hit. Kprobes' trampoline
-handler calls the user-specified handler associated with the kretprobe,
-then sets the saved instruction pointer to the saved return address,
-and that's where execution resumes upon return from the trap.
+handler calls the user-specified return handler associated with the
+kretprobe, then sets the saved instruction pointer to the saved return
+address, and that's where execution resumes upon return from the trap.

While the probed function is executing, its return address is
stored in an object of type kretprobe_instance. Before calling
@@ -131,6 +133,30 @@ zero when the return probe is registered
time the probed function is entered but there is no kretprobe_instance
object available for establishing the return probe.

+1.3.2 Kretprobe entry-handler
+
+Kretprobes also provides an optional user-specified handler which runs
+on function entry. This handler is specified by setting the entry_handler
+field of the kretprobe struct. Whenever the kprobe placed by kretprobe at the
+function entry is hit, the user-defined entry_handler, if any, is invoked.
+If the entry_handler returns 0 (success) then a corresponding return handler
+is guaranteed to be called upon function return. If the entry_handler
+returns a non-zero error then Kprobes leaves the return address as is, and
+the kretprobe has no further effect for that particular function instance.
+
+Multiple entry and return handler invocations are matched using the unique
+kretprobe_instance object associated with them. Additionally, a user
+may also specify per return-instance private data to be part of each
+kretprobe_instance object. This is especially useful when sharing private
+data between corresponding user entry and return handlers. The size of each
+private data object can be specified at kretprobe registration time by
+setting the data_size field of the kretprobe struct. This data can be
+accessed through the data field of each kretprobe_instance object.
+
+In case probed function is entered but there is no kretprobe_instance
+object available, then in addition to incrementing the nmissed count,
+the user entry_handler invocation is also skipped.
+
2. Architectures Supported

Kprobes, jprobes, and return probes are implemented on the following
@@ -273,6 +299,8 @@ of interest:
- ret_addr: the return address
- rp: points to the corresponding kretprobe object
- task: points to the corresponding task struct
+- data: points to per return-instance private data; see "Kretprobe
+ entry-handler" for details.

The regs_return_value(regs) macro provides a simple abstraction to
extract the return value from the appropriate register as defined by
@@ -555,23 +583,52 @@ report failed calls to sys_open().
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
+#include <linux/ktime.h>
+
+/* per-instance private data */
+struct my_data {
+ ktime_t entry_stamp;
+};

static const char *probed_func = "sys_open";

-/* Return-probe handler: If the probed function fails, log the return value. */
-static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+/* Timestamp function entry. */
+static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+ struct my_data *data;
+
+ if(!current->mm)
+ return 1; /* skip kernel threads */
+
+ data = (struct my_data *)ri->data;
+ data->entry_stamp = ktime_get();
+ return 0;
+}
+
+/* If the probed function failed, log the return value and duration.
+ * Duration may turn out to be zero consistently, depending upon the
+ * granularity of time accounting on the platform. */
+static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
int retval = regs_return_value(regs);
+ struct my_data *data = (struct my_data *)ri->data;
+ s64 delta;
+ ktime_t now;
+
if (retval < 0) {
- printk("%s returns %d\n", probed_func, retval);
+ now = ktime_get();
+ delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
+ printk("%s: return val = %d (duration = %lld ns)\n",
+ probed_func, retval, delta);
}
return 0;
}

static struct kretprobe my_kretprobe = {
- .handler = ret_handler,
- /* Probe up to 20 instances concurrently. */
- .maxactive = 20
+ .handler = return_handler,
+ .entry_handler = entry_handler,
+ .data_size = sizeof(struct my_data),
+ .maxactive = 20, /* probe up to 20 instances concurrently */
};

static int __init kretprobe_init(void)
@@ -583,7 +640,7 @@ static int __init kretprobe_init(void)
printk("register_kretprobe failed, returned %d\n", ret);
return -1;
}
- printk("Planted return probe at %p\n", my_kretprobe.kp.addr);
+ printk("Kretprobe active on %s\n", my_kretprobe.kp.symbol_name);
return 0;
}

@@ -593,7 +650,7 @@ static void __exit kretprobe_exit(void)
printk("kretprobe unregistered\n");
/* nmissed > 0 suggests that maxactive was set too low. */
printk("Missed probing %d instances of %s\n",
- my_kretprobe.nmissed, probed_func);
+ my_kretprobe.nmissed, probed_func);
}

module_init(kretprobe_init)
diff -upNr -X /home/guest/patches/dontdiff.txt linux-2.6.24-rc8-mm1/include/linux/kprobes.h linux-2.6.24-rc8-mm1_kp/include/linux/kprobes.h
--- linux-2.6.24-rc8-mm1/include/linux/kprobes.h 2008-01-26 16:46:40.000000000 +0530
+++ linux-2.6.24-rc8-mm1_kp/include/linux/kprobes.h 2008-01-26 15:30:47.000000000 +0530
@@ -152,8 +152,10 @@ static inline int arch_trampoline_kprobe
struct kretprobe {
struct kprobe kp;
kretprobe_handler_t handler;
+ kretprobe_handler_t entry_handler;
int maxactive;
int nmissed;
+ size_t data_size;
struct hlist_head free_instances;
struct hlist_head used_instances;
};
@@ -164,6 +166,7 @@ struct kretprobe_instance {
struct kretprobe *rp;
kprobe_opcode_t *ret_addr;
struct task_struct *task;
+ char data[0];
};

struct kretprobe_blackpoint {
diff -upNr -X /home/guest/patches/dontdiff.txt linux-2.6.24-rc8-mm1/kernel/kprobes.c linux-2.6.24-rc8-mm1_kp/kernel/kprobes.c
--- linux-2.6.24-rc8-mm1/kernel/kprobes.c 2008-01-26 16:46:43.000000000 +0530
+++ linux-2.6.24-rc8-mm1_kp/kernel/kprobes.c 2008-01-26 15:16:59.000000000 +0530
@@ -699,6 +699,12 @@ static int __kprobes pre_handler_kretpro
struct kretprobe_instance, uflist);
ri->rp = rp;
ri->task = current;
+
+ if (rp->entry_handler && rp->entry_handler(ri, regs)) {
+ spin_unlock_irqrestore(&kretprobe_lock, flags);
+ return 0;
+ }
+
arch_prepare_kretprobe(ri, regs);

/* XXX(hch): why is there no hlist_move_head? */
@@ -745,7 +751,8 @@ int __kprobes register_kretprobe(struct
INIT_HLIST_HEAD(&rp->used_instances);
INIT_HLIST_HEAD(&rp->free_instances);
for (i = 0; i < rp->maxactive; i++) {
- inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
+ inst = kmalloc(sizeof(struct kretprobe_instance) +
+ rp->data_size, GFP_KERNEL);
if (inst == NULL) {
free_rp_inst(rp);
return -ENOMEM;
diff -upNr -X /home/guest/patches/dontdiff.txt linux-2.6.24-rc8-mm1/kernel/test_kprobes.c linux-2.6.24-rc8-mm1_kp/kernel/test_kprobes.c
--- linux-2.6.24-rc8-mm1/kernel/test_kprobes.c 2008-01-26 16:46:47.000000000 +0530
+++ linux-2.6.24-rc8-mm1_kp/kernel/test_kprobes.c 2008-01-26 16:34:57.000000000 +0530
@@ -135,6 +135,12 @@ static int test_jprobe(void)
#ifdef CONFIG_KRETPROBES
static u32 krph_val;

+static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+ krph_val = (rand1 / div_factor);
+ return 0;
+}
+
static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
unsigned long ret = regs_return_value(regs);
@@ -144,13 +150,19 @@ static int return_handler(struct kretpro
printk(KERN_ERR "Kprobe smoke test failed: "
"incorrect value in kretprobe handler\n");
}
+ if (krph_val == 0) {
+ handler_errors++;
+ printk(KERN_ERR "Kprobe smoke test failed: "
+ "call to kretprobe entry handler failed\n");
+ }

- krph_val = (rand1 / div_factor);
+ krph_val = rand1;
return 0;
}

static struct kretprobe rp = {
.handler = return_handler,
+ .entry_handler = entry_handler,
.kp.symbol_name = "kprobe_target"
};

@@ -167,7 +179,7 @@ static int test_kretprobe(void)

ret = kprobe_target(rand1);
unregister_kretprobe(&rp);
- if (krph_val == 0) {
+ if (krph_val != rand1) {
printk(KERN_ERR "Kprobe smoke test failed: "
"kretprobe handler not called\n");
handler_errors++;


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