ARM kprobes: prevent some functions involved with kprobes from being probed

[linux-2.6/linux-loongson.git] / arch / arm / kernel / kprobes.c

/*
 * 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>

/*
 * This undefined instruction must be unique and
 * reserved solely for kprobes' use.
 */
#define KPROBE_BREAKPOINT_INSTRUCTION   0xe7f001f8

#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.
                 */
        }
}

static 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;
}

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;
}