/*
* 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/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/opcodes.h>
#include <asm/cacheflush.h>
#include <linux/percpu.h>
#include <linux/bug.h>
#include <asm/patch.h>
#include <asm/sections.h>
#include "../decode-arm.h"
#include "../decode-thumb.h"
#include "core.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, size) \
flush_icache_range((unsigned long)(addr), \
(unsigned long)(addr) + \
(size))
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;
bool thumb;
kprobe_decode_insn_t *decode_insn;
const union decode_action *actions;
int is;
const struct decode_checker **checkers;
#ifdef CONFIG_THUMB2_KERNEL
thumb = true;
addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
if (is_wide_instruction(insn)) {
u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
insn = __opcode_thumb32_compose(insn, inst2);
decode_insn = thumb32_probes_decode_insn;
actions = kprobes_t32_actions;
checkers = kprobes_t32_checkers;
} else {
decode_insn = thumb16_probes_decode_insn;
actions = kprobes_t16_actions;
checkers = kprobes_t16_checkers;
}
#else /* !CONFIG_THUMB2_KERNEL */
thumb = false;
if (addr & 0x3)
return -EINVAL;
insn = __mem_to_opcode_arm(*p->addr);
decode_insn = arm_probes_decode_insn;
actions = kprobes_arm_actions;
checkers = kprobes_arm_checkers;
#endif
p->opcode = insn;
p->ainsn.insn = tmp_insn;
switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
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,
sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
p->ainsn.insn_fn = (probes_insn_fn_t *)
((uintptr_t)p->ainsn.insn | thumb);
break;
case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
p->ainsn.insn = NULL;
break;
}
/*
* Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
* 'str r0, [sp, #-68]' should also be prohibited.
* See __und_svc.
*/
if ((p->ainsn.stack_space < 0) ||
(p->ainsn.stack_space > MAX_STACK_SIZE))
return -EINVAL;
return 0;
}
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
unsigned int brkp;
void *addr;
if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
/* Remove any Thumb flag */
addr = (void *)((uintptr_t)p->addr & ~1);
if (is_wide_instruction(p->opcode))
brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
else
brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
} else {
kprobe_opcode_t insn = p->opcode;
addr = p->addr;
brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
if (insn >= 0xe0000000)
brkp |= 0xe0000000; /* Unconditional instruction */
else
brkp |= insn & 0xf0000000; /* Copy condition from insn */
}
patch_text(addr, brkp);
}
/*
* The actual disarming is done here on each CPU and synchronized using
* stop_machine. This synchronization is necessary on SMP to avoid removing
* a probe between the moment the 'Undefined Instruction' exception is raised
* and the moment the exception handler reads the faulting instruction from
* memory. It is also needed to atomically set the two half-words of a 32-bit
* Thumb breakpoint.
*/
struct patch {
void *addr;
unsigned int insn;
};
static int __kprobes_remove_breakpoint(void *data)
{
struct patch *p = data;
__patch_text(p->addr, p->insn);
return 0;
}
void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
{
struct patch p = {
.addr = addr,
.insn = insn,
};
stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
cpu_online_mask);
}
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
p->opcode);
}
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
if (p->ainsn.insn) {
free_insn_slot(p->ainsn.insn, 0);
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)
{
__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
kcb->kprobe_status = kcb->prev_kprobe.status;
}
static void __kprobes set_current_kprobe(struct kprobe *p)
{
__this_cpu_write(current_kprobe, p);
}
static void __kprobes
singlestep_skip(struct kprobe *p, struct pt_regs *regs)
{
#ifdef CONFIG_THUMB2_KERNEL
regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
if (is_wide_instruction(p->opcode))
regs->ARM_pc += 4;
else
regs->ARM_pc += 2;
#else
regs->ARM_pc += 4;
#endif
}
static inline void __kprobes
singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
p->ainsn.insn_singlestep(p->opcode, &p->ainsn, 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;
kcb = get_kprobe_ctlblk();
cur = kprobe_running();
#ifdef CONFIG_THUMB2_KERNEL
/*
* First look for a probe which was registered using an address with
* bit 0 set, this is the usual situation for pointers to Thumb code.
* If not found, fallback to looking for one with bit 0 clear.
*/
p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
if (!p)
p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
#else /* ! CONFIG_THUMB2_KERNEL */
p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
#endif
if (p) {
if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
/*
* Probe hit but conditional execution check failed,
* so just skip the instruction and continue as if
* nothing had happened.
* In this case, we can skip recursing check too.
*/
singlestep_skip(p, regs);
} else if (cur) {
/* Kprobe is pending, so we're recursing. */
switch (kcb->kprobe_status) {
case KPROBE_HIT_ACTIVE:
case KPROBE_HIT_SSDONE:
case KPROBE_HIT_SS:
/* 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;
case KPROBE_REENTER:
/* A nested probe was hit in FIQ, it is a BUG */
pr_warn("Unrecoverable kprobe detected.\n");
dump_kprobe(p);
/* fall through */
default:
/* impossible cases */
BUG();
}
} else {
/* Probe hit and conditional execution check ok. */
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 will
* modify the execution path and no need to single
* stepping. Let's just reset current kprobe and exit.
*/
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 {
/*
* 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.
*/
}
}
static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
unsigned long flags;
local_irq_save(flags);
kprobe_handler(regs);
local_irq_restore(flags);
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.
*/
void __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"
#ifdef CONFIG_THUMB2_KERNEL
"bx lr \n\t"
#else
"mov pc, lr \n\t"
#endif
: : : "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 *tmp;
unsigned long flags, orig_ret_address = 0;
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
kprobe_opcode_t *correct_ret_addr = NULL;
INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
/*
* 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, tmp, head, hlist) {
if (ri->task != current)
/* another task is sharing our hash bucket */
continue;
orig_ret_address = (unsigned long)ri->ret_addr;
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);
correct_ret_addr = ri->ret_addr;
hlist_for_each_entry_safe(ri, tmp, head, hlist) {
if (ri->task != current)
/* another task is sharing our hash bucket */
continue;
orig_ret_address = (unsigned long)ri->ret_addr;
if (ri->rp && ri->rp->handler) {
__this_cpu_write(current_kprobe, &ri->rp->kp);
get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
ri->ret_addr = correct_ret_addr;
ri->rp->handler(ri, regs);
__this_cpu_write(current_kprobe, NULL);
}
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_hash_unlock(current, &flags);
hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
kfree(ri);
}
return (void *)orig_ret_address;
}
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 arch_trampoline_kprobe(struct kprobe *p)
{
return 0;
}
#ifdef CONFIG_THUMB2_KERNEL
static struct undef_hook kprobes_thumb16_break_hook = {
.instr_mask = 0xffff,
.instr_val = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
.cpsr_mask = MODE_MASK,
.cpsr_val = SVC_MODE,
.fn = kprobe_trap_handler,
};
static struct undef_hook kprobes_thumb32_break_hook = {
.instr_mask = 0xffffffff,
.instr_val = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
.cpsr_mask = MODE_MASK,
.cpsr_val = SVC_MODE,
.fn = kprobe_trap_handler,
};
#else /* !CONFIG_THUMB2_KERNEL */
static struct undef_hook kprobes_arm_break_hook = {
.instr_mask = 0x0fffffff,
.instr_val = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
.cpsr_mask = MODE_MASK,
.cpsr_val = SVC_MODE,
.fn = kprobe_trap_handler,
};
#endif /* !CONFIG_THUMB2_KERNEL */
int __init arch_init_kprobes()
{
arm_probes_decode_init();
#ifdef CONFIG_THUMB2_KERNEL
register_undef_hook(&kprobes_thumb16_break_hook);
register_undef_hook(&kprobes_thumb32_break_hook);
#else
register_undef_hook(&kprobes_arm_break_hook);
#endif
return 0;
}
bool arch_within_kprobe_blacklist(unsigned long addr)
{
void *a = (void *)addr;
return __in_irqentry_text(addr) ||
in_entry_text(addr) ||
in_idmap_text(addr) ||
memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
}
