/*
* arch/arm/kernel/kprobes.c
*
* Kprobes on ARM
*
* Abhishek Sagar <sagar.abhishek@gmail.com>
* Copyright (C) 2006, 2007 Motorola Inc.
*
* Nicolas Pitre <nico@marvell.com>
* Copyright (C) 2007 Marvell Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* 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.
*/
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/cacheflush.h>
#define MIN_STACK_SIZE(addr) \
min((unsigned long)MAX_STACK_SIZE, \
(unsigned long)current_thread_info() + THREAD_START_SP - (addr))
#define flush_insns(addr, cnt) \
flush_icache_range((unsigned long)(addr), \
(unsigned long)(addr) + \
sizeof(kprobe_opcode_t) * (cnt))
/* Used as a marker in ARM_pc to note when we're in a jprobe. */
#define JPROBE_MAGIC_ADDR 0xffffffff
DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
kprobe_opcode_t insn;
kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
unsigned long addr = (unsigned long)p->addr;
int is;
if (addr & 0x3 || in_exception_text(addr))
return -EINVAL;
insn = *p->addr;
p->opcode = insn;
p->ainsn.insn = tmp_insn;
switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
case INSN_REJECTED: /* not supported */
return -EINVAL;
case INSN_GOOD: /* instruction uses slot */
p->ainsn.insn = get_insn_slot();
if (!p->ainsn.insn)
return -ENOMEM;
for (is = 0; is < MAX_INSN_SIZE; ++is)
p->ainsn.insn[is] = tmp_insn[is];
flush_insns(&p->ainsn.insn, MAX_INSN_SIZE);
break;
case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
p->ainsn.insn = NULL;
break;
}
return 0;
}
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
*p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
flush_insns(p->addr, 1);
}
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
*p->addr = p->opcode;
flush_insns(p->addr, 1);
}
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
if (p->ainsn.insn) {
mutex_lock(&kprobe_mutex);
free_insn_slot(p->ainsn.insn, 0);
mutex_unlock(&kprobe_mutex);
p->ainsn.insn = NULL;
}
}
static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
kcb->prev_kprobe.kp = kprobe_running();
kcb->prev_kprobe.status = kcb->kprobe_status;
}
static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
kcb->kprobe_status = kcb->prev_kprobe.status;
}
static void __kprobes set_current_kprobe(struct kprobe *p)
{
__get_cpu_var(current_kprobe) = p;
}
static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb)
{
regs->ARM_pc += 4;
p->ainsn.insn_handler(p, regs);
}
/*
* Called with IRQs disabled. IRQs must remain disabled from that point
* all the way until processing this kprobe is complete. The current
* kprobes implementation cannot process more than one nested level of
* kprobe, and that level is reserved for user kprobe handlers, so we can't
* risk encountering a new kprobe in an interrupt handler.
*/
void __kprobes kprobe_handler(struct pt_regs *regs)
{
struct kprobe *p, *cur;
struct kprobe_ctlblk *kcb;
kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc;
kcb = get_kprobe_ctlblk();
cur = kprobe_running();
p = get_kprobe(addr);
if (p) {
if (cur) {
/* Kprobe is pending, so we're recursing. */
switch (kcb->kprobe_status) {
case KPROBE_HIT_ACTIVE:
case KPROBE_HIT_SSDONE:
/* A pre- or post-handler probe got us here. */
kprobes_inc_nmissed_count(p);
save_previous_kprobe(kcb);
set_current_kprobe(p);
kcb->kprobe_status = KPROBE_REENTER;
singlestep(p, regs, kcb);
restore_previous_kprobe(kcb);
break;
default:
/* impossible cases */
BUG();
}
} else {
set_current_kprobe(p);
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
/*
* If we have no pre-handler or it returned 0, we
* continue with normal processing. If we have a
* pre-handler and it returned non-zero, it prepped
* for calling the break_handler below on re-entry,
* so get out doing nothing more here.
*/
if (!p->pre_handler || !p->pre_handler(p, regs)) {
kcb->kprobe_status = KPROBE_HIT_SS;
singlestep(p, regs, kcb);
if (p->post_handler) {
kcb->kprobe_status = KPROBE_HIT_SSDONE;
p->post_handler(p, regs, 0);
}
reset_current_kprobe();
}
}
} else if (cur) {
/* We probably hit a jprobe. Call its break handler. */
if (cur->break_handler && cur->break_handler(cur, regs)) {
kcb->kprobe_status = KPROBE_HIT_SS;
singlestep(cur, regs, kcb);
if (cur->post_handler) {
kcb->kprobe_status = KPROBE_HIT_SSDONE;
cur->post_handler(cur, regs, 0);
}
}
reset_current_kprobe();
} else {
/*
* The probe was removed and a race is in progress.
* There is nothing we can do about it. Let's restart
* the instruction. By the time we can restart, the
* real instruction will be there.
*/
}
}
int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
kprobe_handler(regs);
return 0;
}
int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
{
struct kprobe *cur = kprobe_running();
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
switch (kcb->kprobe_status) {
case KPROBE_HIT_SS:
case KPROBE_REENTER:
/*
* We are here because the instruction being single
* stepped caused a page fault. We reset the current
* kprobe and the PC to point back to the probe address
* and allow the page fault handler to continue as a
* normal page fault.
*/
regs->ARM_pc = (long)cur->addr;
if (kcb->kprobe_status == KPROBE_REENTER) {
restore_previous_kprobe(kcb);
} else {
reset_current_kprobe();
}
break;
case KPROBE_HIT_ACTIVE:
case KPROBE_HIT_SSDONE:
/*
* We increment the nmissed count for accounting,
* we can also use npre/npostfault count for accounting
* these specific fault cases.
*/
kprobes_inc_nmissed_count(cur);
/*
* We come here because instructions in the pre/post
* handler caused the page_fault, this could happen
* if handler tries to access user space by
* copy_from_user(), get_user() etc. Let the
* user-specified handler try to fix it.
*/
if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
return 1;
break;
default:
break;
}
return 0;
}
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data)
{
/*
* notify_die() is currently never called on ARM,
* so this callback is currently empty.
*/
return NOTIFY_DONE;
}
/*
* When a retprobed function returns, trampoline_handler() is called,
* calling the kretprobe's handler. We construct a struct pt_regs to
* give a view of registers r0-r11 to the user return-handler. This is
* not a complete pt_regs structure, but that should be plenty sufficient
* for kretprobe handlers which should normally be interested in r0 only
* anyway.
*/
static void __attribute__((naked)) __kprobes kretprobe_trampoline(void)
{
__asm__ __volatile__ (
"stmdb sp!, {r0 - r11} \n\t"
"mov r0, sp \n\t"
"bl trampoline_handler \n\t"
"mov lr, r0 \n\t"
"ldmia sp!, {r0 - r11} \n\t"
"mov pc, lr \n\t"
: : : "memory");
}
/* Called from kretprobe_trampoline */
static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
{
struct kretprobe_instance *ri = NULL;
struct hlist_head *head, empty_rp;
struct hlist_node *node, *tmp;
unsigned long flags, orig_ret_address = 0;
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
INIT_HLIST_HEAD(&empty_rp);
spin_lock_irqsave(&kretprobe_lock, flags);
head = kretprobe_inst_table_head(current);
/*
* It is possible to have multiple instances associated with a given
* task either because multiple functions in the call path have
* a return probe installed on them, and/or more than one return
* probe was registered for a target function.
*
* We can handle this because:
* - instances are always inserted at the head of the list
* - when multiple return probes are registered for the same
* function, the first instance's ret_addr will point to the
* real return address, and all the rest will point to
* kretprobe_trampoline
*/
hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
if (ri->task != current)
/* another task is sharing our hash bucket */
continue;
if (ri->rp && ri->rp->handler) {
__get_cpu_var(current_kprobe) = &ri->rp->kp;
get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
ri->rp->handler(ri, regs);
__get_cpu_var(current_kprobe) = NULL;
}
orig_ret_address = (unsigned long)ri->ret_addr;
recycle_rp_inst(ri, &empty_rp);
if (orig_ret_address != trampoline_address)
/*
* This is the real return address. Any other
* instances associated with this task are for
* other calls deeper on the call stack
*/
break;
}
kretprobe_assert(ri, orig_ret_address, trampoline_address);
spin_unlock_irqrestore(&kretprobe_lock, flags);
hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
kfree(ri);
}
return (void *)orig_ret_address;
}
/* Called with kretprobe_lock held. */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
/* Replace the return addr with trampoline addr. */
regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
}
int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
struct jprobe *jp = container_of(p, struct jprobe, kp);
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
long sp_addr = regs->ARM_sp;
kcb->jprobe_saved_regs = *regs;
memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
regs->ARM_pc = (long)jp->entry;
regs->ARM_cpsr |= PSR_I_BIT;
preempt_disable();
return 1;
}
void __kprobes jprobe_return(void)
{
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
__asm__ __volatile__ (
/*
* Setup an empty pt_regs. Fill SP and PC fields as
* they're needed by longjmp_break_handler.
*/
"sub sp, %0, %1 \n\t"
"ldr r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
"str %0, [sp, %2] \n\t"
"str r0, [sp, %3] \n\t"
"mov r0, sp \n\t"
"bl kprobe_handler \n\t"
/*
* Return to the context saved by setjmp_pre_handler
* and restored by longjmp_break_handler.
*/
"ldr r0, [sp, %4] \n\t"
"msr cpsr_cxsf, r0 \n\t"
"ldmia sp, {r0 - pc} \n\t"
:
: "r" (kcb->jprobe_saved_regs.ARM_sp),
"I" (sizeof(struct pt_regs)),
"J" (offsetof(struct pt_regs, ARM_sp)),
"J" (offsetof(struct pt_regs, ARM_pc)),
"J" (offsetof(struct pt_regs, ARM_cpsr))
: "memory", "cc");
}
int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
long orig_sp = regs->ARM_sp;
struct jprobe *jp = container_of(p, struct jprobe, kp);
if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
if (orig_sp != stack_addr) {
struct pt_regs *saved_regs =
(struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
printk("current sp %lx does not match saved sp %lx\n",
orig_sp, stack_addr);
printk("Saved registers for jprobe %p\n", jp);
show_regs(saved_regs);
printk("Current registers\n");
show_regs(regs);
BUG();
}
*regs = kcb->jprobe_saved_regs;
memcpy((void *)stack_addr, kcb->jprobes_stack,
MIN_STACK_SIZE(stack_addr));
preempt_enable_no_resched();
return 1;
}
return 0;
}
int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
return 0;
}
static struct undef_hook kprobes_break_hook = {
.instr_mask = 0xffffffff,
.instr_val = KPROBE_BREAKPOINT_INSTRUCTION,
.cpsr_mask = MODE_MASK,
.cpsr_val = SVC_MODE,
.fn = kprobe_trap_handler,
};
int __init arch_init_kprobes()
{
arm_kprobe_decode_init();
register_undef_hook(&kprobes_break_hook);
return 0;
}
