kprobes.c

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/*
 * arch/arm/kernel/kprobes.c
 *
 * Kprobes on ARM
 *
 * Abhishek Sagar <[email protected]>
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * Nicolas Pitre <[email protected]>
 * 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/stringify.h>
#include <asm/traps.h>
#include <asm/cacheflush.h>

#include "kprobes.h"
#include "patch.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))

/* 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;
    bool thumb;
    kprobe_decode_insn_t *decode_insn;
    int is;

    if (in_exception_text(addr))
        return -EINVAL;

#ifdef CONFIG_THUMB2_KERNEL
    thumb = true;
    addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
    insn = ((u16 *)addr)[0];
    if (is_wide_instruction(insn)) {
        insn <<= 16;
        insn |= ((u16 *)addr)[1];
        decode_insn = thumb32_kprobe_decode_insn;
    } else
        decode_insn = thumb16_kprobe_decode_insn;
#else /* !CONFIG_THUMB2_KERNEL */
    thumb = false;
    if (addr & 0x3)
        return -EINVAL;
    insn = *p->addr;
    decode_insn = arm_kprobe_decode_insn;
#endif

    p->opcode = insn;
    p->ainsn.insn = tmp_insn;

    switch ((*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,
                sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
        p->ainsn.insn_fn = (kprobe_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;
    }

    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.
 */
int __kprobes __arch_disarm_kprobe(void *p)
{
    struct kprobe *kp = p;
    void *addr = (void *)((uintptr_t)kp->addr & ~1);

    __patch_text(addr, kp->opcode);

    return 0;
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
    stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
}

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)
{
    __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_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, 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 (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 if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
            /* 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 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 {
            /*
             * Probe hit but conditional execution check failed,
             * so just skip the instruction and continue as if
             * nothing had happened.
             */
            singlestep_skip(p, regs);
        }
    } 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 __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 *node, *tmp;
    unsigned long flags, orig_ret_address = 0;
    unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

    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, 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);
    kretprobe_hash_unlock(current, &flags);

    hlist_for_each_entry_safe(ri, node, 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 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;
    long cpsr;

    kcb->jprobe_saved_regs = *regs;
    memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
    regs->ARM_pc = (long)jp->entry;

    cpsr = regs->ARM_cpsr | PSR_I_BIT;
#ifdef CONFIG_THUMB2_KERNEL
    /* Set correct Thumb state in cpsr */
    if (regs->ARM_pc & 1)
        cpsr |= PSR_T_BIT;
    else
        cpsr &= ~PSR_T_BIT;
#endif
    regs->ARM_cpsr = cpsr;

    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.
         *
         * We allocate some slack between the original SP and start of
         * our fabricated regs. To be precise we want to have worst case
         * covered which is STMFD with all 16 regs so we allocate 2 *
         * sizeof(struct_pt_regs)).
         *
         * This is to prevent any simulated instruction from writing
         * over the regs when they are accessing the stack.
         */
#ifdef CONFIG_THUMB2_KERNEL
        "sub    r0, %0, %1      \n\t"
        "mov    sp, r0          \n\t"
#else
        "sub    sp, %0, %1      \n\t"
#endif
        "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.
         */
#ifdef CONFIG_THUMB2_KERNEL
        "ldr    lr, [sp, %2]        \n\t" /* lr = saved sp */
        "ldrd   r0, r1, [sp, %5]    \n\t" /* r0,r1 = saved lr,pc */
        "ldr    r2, [sp, %4]        \n\t" /* r2 = saved psr */
        "stmdb  lr!, {r0, r1, r2}   \n\t" /* push saved lr and */
                              /* rfe context */
        "ldmia  sp, {r0 - r12}      \n\t"
        "mov    sp, lr          \n\t"
        "ldr    lr, [sp], #4        \n\t"
        "rfeia  sp!         \n\t"
#else
        "ldr    r0, [sp, %4]        \n\t"
        "msr    cpsr_cxsf, r0       \n\t"
        "ldmia  sp, {r0 - pc}       \n\t"
#endif
        :
        : "r" (kcb->jprobe_saved_regs.ARM_sp),
          "I" (sizeof(struct pt_regs) * 2),
          "J" (offsetof(struct pt_regs, ARM_sp)),
          "J" (offsetof(struct pt_regs, ARM_pc)),
          "J" (offsetof(struct pt_regs, ARM_cpsr)),
          "J" (offsetof(struct pt_regs, ARM_lr))
        : "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;
}

#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_kprobe_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;
}