diff options
| -rw-r--r-- | Documentation/kprobes.txt | 81 | ||||
| -rw-r--r-- | include/linux/kprobes.h | 3 | ||||
| -rw-r--r-- | kernel/kprobes.c | 9 | ||||
| -rw-r--r-- | kernel/test_kprobes.c | 16 |
4 files changed, 94 insertions, 15 deletions
diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt index 53a6389..30c1017 100644 --- a/Documentation/kprobes.txt +++ b/Documentation/kprobes.txt @@ -96,7 +96,9 @@ or in registers (e.g., for x86_64 or for an i386 fastcall function). 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 at the trampoline. 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, and is incremented every 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 @@ -274,6 +300,8 @@ 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 @@ -556,23 +584,52 @@ 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) @@ -584,7 +641,7 @@ 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; } @@ -594,7 +651,7 @@ 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 --git a/include/linux/kprobes.h b/include/linux/kprobes.h index 6168c0a..4a6ce82 100644 --- a/include/linux/kprobes.h +++ b/include/linux/kprobes.h @@ -152,8 +152,10 @@ static inline int arch_trampoline_kprobe(struct kprobe *p) 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 --git a/kernel/kprobes.c b/kernel/kprobes.c index d0493ea..7a86e64 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -699,6 +699,12 @@ static int __kprobes pre_handler_kretprobe(struct kprobe *p, 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 kretprobe *rp) 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 --git a/kernel/test_kprobes.c b/kernel/test_kprobes.c index 88cdb10..06b6395 100644 --- a/kernel/test_kprobes.c +++ b/kernel/test_kprobes.c @@ -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 kretprobe_instance *ri, struct pt_regs *regs) 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++; |
