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linux-stable/kernel/kprobes.c
Rusty Lynch 802eae7c80 [PATCH] Return probe redesign: architecture independent changes 
The following is the second version of the function return probe patches
I sent out earlier this week.  Changes since my last submission include:

* Fix in ppc64 code removing an unneeded call to re-enable preemption
* Fix a build problem in ia64 when kprobes was turned off
* Added another BUG_ON check to each of the architecture trampoline
  handlers

My initial patch description ==>

 From my experiences with adding return probes to x86_64 and ia64, and the
feedback on LKML to those patches, I think we can simplify the design
for return probes.

The following patch tweaks the original design such that:

* Instead of storing the stack address in the return probe instance, the
  task pointer is stored.  This gives us all we need in order to:
    - find the correct return probe instance when we enter the trampoline
      (even if we are recursing)
    - find all left-over return probe instances when the task is going away

  This has the side effect of simplifying the implementation since more
  work can be done in kernel/kprobes.c since architecture specific knowledge
  of the stack layout is no longer required.  Specifically, we no longer have:
	- arch_get_kprobe_task()
	- arch_kprobe_flush_task()
	- get_rp_inst_tsk()
	- get_rp_inst()
	- trampoline_post_handler() <see next bullet>

* Instead of splitting the return probe handling and cleanup logic across
  the pre and post trampoline handlers, all the work is pushed into the
  pre function (trampoline_probe_handler), and then we skip single stepping
  the original function.  In this case the original instruction to be single
  stepped was just a NOP, and we can do without the extra interruption.

The new flow of events to having a return probe handler execute when a target
function exits is:

* At system initialization time, a kprobe is inserted at the beginning of
  kretprobe_trampoline.  kernel/kprobes.c use to handle this on it's own,
  but ia64 needed to do this a little differently (i.e. a function pointer
  is really a pointer to a structure containing the instruction pointer and
  a global pointer), so I added the notion of arch_init(), so that
  kernel/kprobes.c:init_kprobes() now allows architecture specific
  initialization by calling arch_init() before exiting.  Each architecture
  now registers a kprobe on it's own trampoline function.

* register_kretprobe() will insert a kprobe at the beginning of the targeted
  function with the kprobe pre_handler set to arch_prepare_kretprobe
  (still no change)

* When the target function is entered, the kprobe is fired, calling
  arch_prepare_kretprobe (still no change)

* In arch_prepare_kretprobe() we try to get a free instance and if one is
  available then we fill out the instance with a pointer to the return probe,
  the original return address, and a pointer to the task structure (instead
  of the stack address.)  Just like before we change the return address
  to the trampoline function and mark the instance as used.

  If multiple return probes are registered for a given target function,
  then arch_prepare_kretprobe() will get called multiple times for the same
  task (since our kprobe implementation is able to handle multiple kprobes
  at the same address.)  Past the first call to arch_prepare_kretprobe,
  we end up with the original address stored in the return probe instance
  pointing to our trampoline function. (This is a significant difference
  from the original arch_prepare_kretprobe design.)

* Target function executes like normal and then returns to kretprobe_trampoline.

* kprobe inserted on the first instruction of kretprobe_trampoline is fired
  and calls trampoline_probe_handler() (no change here)

* trampoline_probe_handler() consumes each of the instances associated with
  the current task by calling the registered handler function and marking
  the instance as unused until an instance is found that has a return address
  different then the trampoline function.

  (change similar to my previous ia64 RFC)

* If the task is killed with some left-over return probe instances (meaning
  that a target function was entered, but never returned), then we just
  free any instances associated with the task.  (Not much different other
  then we can handle this without calling architecture specific functions.)

  There is a known problem that this patch does not yet solve where
  registering a return probe flush_old_exec or flush_thread will put us
  in a bad state.  Most likely the best way to handle this is to not allow
  registering return probes on these two functions.

  (Significant change)

This patch series applies to the 2.6.12-rc6-mm1 kernel, and provides:
  * kernel/kprobes.c changes
  * i386 patch of existing return probes implementation
  * x86_64 patch of existing return probe implementation
  * ia64 implementation
  * ppc64 implementation (provided by Ananth)

This patch implements the architecture independant changes for a reworking
of the kprobes based function return probes design. Changes include:

  * Removing functions for querying a return probe instance off a stack address
  * Removing the stack_addr field from the kretprobe_instance definition,
    and adding a task pointer
  * Adding architecture specific initialization via arch_init()
  * Removing extern definitions for the architecture trampoline functions
    (this isn't needed anymore since the architecture handles the
     initialization of the kprobe in the return probe trampoline function.)

Signed-off-by: Rusty Lynch <rusty.lynch@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-27 15:23:52 -07:00

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/*
* Kernel Probes (KProbes)
* kernel/kprobes.c
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) IBM Corporation, 2002, 2004
*
* 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
* Probes initial implementation (includes suggestions from
* Rusty Russell).
* 2004-Aug Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
* hlists and exceptions notifier as suggested by Andi Kleen.
* 2004-July Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
* interface to access function arguments.
* 2004-Sep Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
* exceptions notifier to be first on the priority list.
* 2005-May Hien Nguyen <hien@us.ibm.com>, Jim Keniston
* <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
* <prasanna@in.ibm.com> added function-return probes.
*/
#include <linux/kprobes.h>
#include <linux/spinlock.h>
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/kdebug.h>
#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
unsigned int kprobe_cpu = NR_CPUS;
static DEFINE_SPINLOCK(kprobe_lock);
static struct kprobe *curr_kprobe;
/*
* kprobe->ainsn.insn points to the copy of the instruction to be
* single-stepped. x86_64, POWER4 and above have no-exec support and
* stepping on the instruction on a vmalloced/kmalloced/data page
* is a recipe for disaster
*/
#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
struct kprobe_insn_page {
struct hlist_node hlist;
kprobe_opcode_t *insns; /* Page of instruction slots */
char slot_used[INSNS_PER_PAGE];
int nused;
};
static struct hlist_head kprobe_insn_pages;
/**
* get_insn_slot() - Find a slot on an executable page for an instruction.
* We allocate an executable page if there's no room on existing ones.
*/
kprobe_opcode_t *get_insn_slot(void)
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
hlist_for_each(pos, &kprobe_insn_pages) {
kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
if (kip->nused < INSNS_PER_PAGE) {
int i;
for (i = 0; i < INSNS_PER_PAGE; i++) {
if (!kip->slot_used[i]) {
kip->slot_used[i] = 1;
kip->nused++;
return kip->insns + (i * MAX_INSN_SIZE);
}
}
/* Surprise! No unused slots. Fix kip->nused. */
kip->nused = INSNS_PER_PAGE;
}
}
/* All out of space. Need to allocate a new page. Use slot 0.*/
kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
if (!kip) {
return NULL;
}
/*
* Use module_alloc so this page is within +/- 2GB of where the
* kernel image and loaded module images reside. This is required
* so x86_64 can correctly handle the %rip-relative fixups.
*/
kip->insns = module_alloc(PAGE_SIZE);
if (!kip->insns) {
kfree(kip);
return NULL;
}
INIT_HLIST_NODE(&kip->hlist);
hlist_add_head(&kip->hlist, &kprobe_insn_pages);
memset(kip->slot_used, 0, INSNS_PER_PAGE);
kip->slot_used[0] = 1;
kip->nused = 1;
return kip->insns;
}
void free_insn_slot(kprobe_opcode_t *slot)
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
hlist_for_each(pos, &kprobe_insn_pages) {
kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
if (kip->insns <= slot &&
slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
int i = (slot - kip->insns) / MAX_INSN_SIZE;
kip->slot_used[i] = 0;
kip->nused--;
if (kip->nused == 0) {
/*
* Page is no longer in use. Free it unless
* it's the last one. We keep the last one
* so as not to have to set it up again the
* next time somebody inserts a probe.
*/
hlist_del(&kip->hlist);
if (hlist_empty(&kprobe_insn_pages)) {
INIT_HLIST_NODE(&kip->hlist);
hlist_add_head(&kip->hlist,
&kprobe_insn_pages);
} else {
module_free(NULL, kip->insns);
kfree(kip);
}
}
return;
}
}
}
/* Locks kprobe: irqs must be disabled */
void lock_kprobes(void)
{
spin_lock(&kprobe_lock);
kprobe_cpu = smp_processor_id();
}
void unlock_kprobes(void)
{
kprobe_cpu = NR_CPUS;
spin_unlock(&kprobe_lock);
}
/* You have to be holding the kprobe_lock */
struct kprobe *get_kprobe(void *addr)
{
struct hlist_head *head;
struct hlist_node *node;
head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
hlist_for_each(node, head) {
struct kprobe *p = hlist_entry(node, struct kprobe, hlist);
if (p->addr == addr)
return p;
}
return NULL;
}
/*
* Aggregate handlers for multiple kprobes support - these handlers
* take care of invoking the individual kprobe handlers on p->list
*/
static int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
struct kprobe *kp;
list_for_each_entry(kp, &p->list, list) {
if (kp->pre_handler) {
curr_kprobe = kp;
if (kp->pre_handler(kp, regs))
return 1;
}
curr_kprobe = NULL;
}
return 0;
}
static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
unsigned long flags)
{
struct kprobe *kp;
list_for_each_entry(kp, &p->list, list) {
if (kp->post_handler) {
curr_kprobe = kp;
kp->post_handler(kp, regs, flags);
curr_kprobe = NULL;
}
}
return;
}
static int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
int trapnr)
{
/*
* if we faulted "during" the execution of a user specified
* probe handler, invoke just that probe's fault handler
*/
if (curr_kprobe && curr_kprobe->fault_handler) {
if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
return 1;
}
return 0;
}
static int aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
{
struct kprobe *kp = curr_kprobe;
if (curr_kprobe && kp->break_handler) {
if (kp->break_handler(kp, regs)) {
curr_kprobe = NULL;
return 1;
}
}
curr_kprobe = NULL;
return 0;
}
struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp)
{
struct hlist_node *node;
struct kretprobe_instance *ri;
hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
return ri;
return NULL;
}
static struct kretprobe_instance *get_used_rp_inst(struct kretprobe *rp)
{
struct hlist_node *node;
struct kretprobe_instance *ri;
hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
return ri;
return NULL;
}
void add_rp_inst(struct kretprobe_instance *ri)
{
/*
* Remove rp inst off the free list -
* Add it back when probed function returns
*/
hlist_del(&ri->uflist);
/* Add rp inst onto table */
INIT_HLIST_NODE(&ri->hlist);
hlist_add_head(&ri->hlist,
&kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
/* Also add this rp inst to the used list. */
INIT_HLIST_NODE(&ri->uflist);
hlist_add_head(&ri->uflist, &ri->rp->used_instances);
}
void recycle_rp_inst(struct kretprobe_instance *ri)
{
/* remove rp inst off the rprobe_inst_table */
hlist_del(&ri->hlist);
if (ri->rp) {
/* remove rp inst off the used list */
hlist_del(&ri->uflist);
/* put rp inst back onto the free list */
INIT_HLIST_NODE(&ri->uflist);
hlist_add_head(&ri->uflist, &ri->rp->free_instances);
} else
/* Unregistering */
kfree(ri);
}
struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk)
{
return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
}
/*
* This function is called from exit_thread or flush_thread when task tk's
* stack is being recycled so that we can recycle any function-return probe
* instances associated with this task. These left over instances represent
* probed functions that have been called but will never return.
*/
void kprobe_flush_task(struct task_struct *tk)
{
struct kretprobe_instance *ri;
struct hlist_head *head;
struct hlist_node *node, *tmp;
unsigned long flags = 0;
spin_lock_irqsave(&kprobe_lock, flags);
head = kretprobe_inst_table_head(current);
hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
if (ri->task == tk)
recycle_rp_inst(ri);
}
spin_unlock_irqrestore(&kprobe_lock, flags);
}
/*
* This kprobe pre_handler is registered with every kretprobe. When probe
* hits it will set up the return probe.
*/
static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
{
struct kretprobe *rp = container_of(p, struct kretprobe, kp);
/*TODO: consider to only swap the RA after the last pre_handler fired */
arch_prepare_kretprobe(rp, regs);
return 0;
}
static inline void free_rp_inst(struct kretprobe *rp)
{
struct kretprobe_instance *ri;
while ((ri = get_free_rp_inst(rp)) != NULL) {
hlist_del(&ri->uflist);
kfree(ri);
}
}
/*
* Keep all fields in the kprobe consistent
*/
static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
{
memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
}
/*
* Add the new probe to old_p->list. Fail if this is the
* second jprobe at the address - two jprobes can't coexist
*/
static int add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
{
struct kprobe *kp;
if (p->break_handler) {
list_for_each_entry(kp, &old_p->list, list) {
if (kp->break_handler)
return -EEXIST;
}
list_add_tail(&p->list, &old_p->list);
} else
list_add(&p->list, &old_p->list);
return 0;
}
/*
* Fill in the required fields of the "manager kprobe". Replace the
* earlier kprobe in the hlist with the manager kprobe
*/
static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
{
copy_kprobe(p, ap);
ap->addr = p->addr;
ap->pre_handler = aggr_pre_handler;
ap->post_handler = aggr_post_handler;
ap->fault_handler = aggr_fault_handler;
ap->break_handler = aggr_break_handler;
INIT_LIST_HEAD(&ap->list);
list_add(&p->list, &ap->list);
INIT_HLIST_NODE(&ap->hlist);
hlist_del(&p->hlist);
hlist_add_head(&ap->hlist,
&kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
}
/*
* This is the second or subsequent kprobe at the address - handle
* the intricacies
* TODO: Move kcalloc outside the spinlock
*/
static int register_aggr_kprobe(struct kprobe *old_p, struct kprobe *p)
{
int ret = 0;
struct kprobe *ap;
if (old_p->pre_handler == aggr_pre_handler) {
copy_kprobe(old_p, p);
ret = add_new_kprobe(old_p, p);
} else {
ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
if (!ap)
return -ENOMEM;
add_aggr_kprobe(ap, old_p);
copy_kprobe(ap, p);
ret = add_new_kprobe(ap, p);
}
return ret;
}
/* kprobe removal house-keeping routines */
static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
{
arch_disarm_kprobe(p);
hlist_del(&p->hlist);
spin_unlock_irqrestore(&kprobe_lock, flags);
arch_remove_kprobe(p);
}
static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
struct kprobe *p, unsigned long flags)
{
list_del(&p->list);
if (list_empty(&old_p->list)) {
cleanup_kprobe(old_p, flags);
kfree(old_p);
} else
spin_unlock_irqrestore(&kprobe_lock, flags);
}
int register_kprobe(struct kprobe *p)
{
int ret = 0;
unsigned long flags = 0;
struct kprobe *old_p;
if ((ret = arch_prepare_kprobe(p)) != 0) {
goto rm_kprobe;
}
spin_lock_irqsave(&kprobe_lock, flags);
old_p = get_kprobe(p->addr);
p->nmissed = 0;
if (old_p) {
ret = register_aggr_kprobe(old_p, p);
goto out;
}
arch_copy_kprobe(p);
INIT_HLIST_NODE(&p->hlist);
hlist_add_head(&p->hlist,
&kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
arch_arm_kprobe(p);
out:
spin_unlock_irqrestore(&kprobe_lock, flags);
rm_kprobe:
if (ret == -EEXIST)
arch_remove_kprobe(p);
return ret;
}
void unregister_kprobe(struct kprobe *p)
{
unsigned long flags;
struct kprobe *old_p;
spin_lock_irqsave(&kprobe_lock, flags);
old_p = get_kprobe(p->addr);
if (old_p) {
if (old_p->pre_handler == aggr_pre_handler)
cleanup_aggr_kprobe(old_p, p, flags);
else
cleanup_kprobe(p, flags);
} else
spin_unlock_irqrestore(&kprobe_lock, flags);
}
static struct notifier_block kprobe_exceptions_nb = {
.notifier_call = kprobe_exceptions_notify,
.priority = 0x7fffffff /* we need to notified first */
};
int register_jprobe(struct jprobe *jp)
{
/* Todo: Verify probepoint is a function entry point */
jp->kp.pre_handler = setjmp_pre_handler;
jp->kp.break_handler = longjmp_break_handler;
return register_kprobe(&jp->kp);
}
void unregister_jprobe(struct jprobe *jp)
{
unregister_kprobe(&jp->kp);
}
#ifdef ARCH_SUPPORTS_KRETPROBES
int register_kretprobe(struct kretprobe *rp)
{
int ret = 0;
struct kretprobe_instance *inst;
int i;
rp->kp.pre_handler = pre_handler_kretprobe;
/* Pre-allocate memory for max kretprobe instances */
if (rp->maxactive <= 0) {
#ifdef CONFIG_PREEMPT
rp->maxactive = max(10, 2 * NR_CPUS);
#else
rp->maxactive = NR_CPUS;
#endif
}
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);
if (inst == NULL) {
free_rp_inst(rp);
return -ENOMEM;
}
INIT_HLIST_NODE(&inst->uflist);
hlist_add_head(&inst->uflist, &rp->free_instances);
}
rp->nmissed = 0;
/* Establish function entry probe point */
if ((ret = register_kprobe(&rp->kp)) != 0)
free_rp_inst(rp);
return ret;
}
#else /* ARCH_SUPPORTS_KRETPROBES */
int register_kretprobe(struct kretprobe *rp)
{
return -ENOSYS;
}
#endif /* ARCH_SUPPORTS_KRETPROBES */
void unregister_kretprobe(struct kretprobe *rp)
{
unsigned long flags;
struct kretprobe_instance *ri;
unregister_kprobe(&rp->kp);
/* No race here */
spin_lock_irqsave(&kprobe_lock, flags);
free_rp_inst(rp);
while ((ri = get_used_rp_inst(rp)) != NULL) {
ri->rp = NULL;
hlist_del(&ri->uflist);
}
spin_unlock_irqrestore(&kprobe_lock, flags);
}
static int __init init_kprobes(void)
{
int i, err = 0;
/* FIXME allocate the probe table, currently defined statically */
/* initialize all list heads */
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
INIT_HLIST_HEAD(&kprobe_table[i]);
INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
}
err = arch_init();
if (!err)
err = register_die_notifier(&kprobe_exceptions_nb);
return err;
}
__initcall(init_kprobes);
EXPORT_SYMBOL_GPL(register_kprobe);
EXPORT_SYMBOL_GPL(unregister_kprobe);
EXPORT_SYMBOL_GPL(register_jprobe);
EXPORT_SYMBOL_GPL(unregister_jprobe);
EXPORT_SYMBOL_GPL(jprobe_return);
EXPORT_SYMBOL_GPL(register_kretprobe);
EXPORT_SYMBOL_GPL(unregister_kretprobe);
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