powerpc/kprobes: Optimize kprobe in kretprobe_trampoline()

[mirror_ubuntu-zesty-kernel.git] / arch / powerpc / kernel / kprobes.c

/*
 *  Kernel Probes (KProbes)
 *
 * 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 contributions from
 *              Rusty Russell).
 * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *              interface to access function arguments.
 * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
 *              for PPC64
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/extable.h>
#include <linux/kdebug.h>
#include <linux/slab.h>
#include <asm/code-patching.h>
#include <asm/cacheflush.h>
#include <asm/sstep.h>
#include <linux/uaccess.h>

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        int ret = 0;
        kprobe_opcode_t insn = *p->addr;

        if ((unsigned long)p->addr & 0x03) {
                printk("Attempt to register kprobe at an unaligned address\n");
                ret = -EINVAL;
        } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
                printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
                ret = -EINVAL;
        }

        /* insn must be on a special executable page on ppc64.  This is
         * not explicitly required on ppc32 (right now), but it doesn't hurt */
        if (!ret) {
                p->ainsn.insn = get_insn_slot();
                if (!p->ainsn.insn)
                        ret = -ENOMEM;
        }

        if (!ret) {
                memcpy(p->ainsn.insn, p->addr,
                                MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
                p->opcode = *p->addr;
                flush_icache_range((unsigned long)p->ainsn.insn,
                        (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
        }

        p->ainsn.boostable = 0;
        return ret;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = BREAKPOINT_INSTRUCTION;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        *p->addr = p->opcode;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

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 prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        enable_single_step(regs);

        /*
         * On powerpc we should single step on the original
         * instruction even if the probed insn is a trap
         * variant as values in regs could play a part in
         * if the trap is taken or not
         */
        regs->nip = (unsigned long)p->ainsn.insn;
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        kcb->prev_kprobe.kp = kprobe_running();
        kcb->prev_kprobe.status = kcb->kprobe_status;
        kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
}

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;
        kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                struct kprobe_ctlblk *kcb)
{
        __this_cpu_write(current_kprobe, p);
        kcb->kprobe_saved_msr = regs->msr;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *)regs->link;

        /* Replace the return addr with trampoline addr */
        regs->link = (unsigned long)kretprobe_trampoline;
}

int __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        int ret = 0;
        unsigned int *addr = (unsigned int *)regs->nip;
        struct kprobe_ctlblk *kcb;

        if (user_mode(regs))
                return 0;

        /*
         * We don't want to be preempted for the entire
         * duration of kprobe processing
         */
        preempt_disable();
        kcb = get_kprobe_ctlblk();

        /* Check we're not actually recursing */
        if (kprobe_running()) {
                p = get_kprobe(addr);
                if (p) {
                        kprobe_opcode_t insn = *p->ainsn.insn;
                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
                                        is_trap(insn)) {
                                /* Turn off 'trace' bits */
                                regs->msr &= ~MSR_SINGLESTEP;
                                regs->msr |= kcb->kprobe_saved_msr;
                                goto no_kprobe;
                        }
                        /* We have reentered the kprobe_handler(), since
                         * another probe was hit while within the handler.
                         * We here save the original kprobes variables and
                         * just single step on the instruction of the new probe
                         * without calling any user handlers.
                         */
                        save_previous_kprobe(kcb);
                        set_current_kprobe(p, regs, kcb);
                        kcb->kprobe_saved_msr = regs->msr;
                        kprobes_inc_nmissed_count(p);
                        prepare_singlestep(p, regs);
                        kcb->kprobe_status = KPROBE_REENTER;
                        return 1;
                } else {
                        if (*addr != BREAKPOINT_INSTRUCTION) {
                                /* If trap variant, then it belongs not to us */
                                kprobe_opcode_t cur_insn = *addr;
                                if (is_trap(cur_insn))
                                        goto no_kprobe;
                                /* The breakpoint instruction was removed by
                                 * another cpu right after we hit, no further
                                 * handling of this interrupt is appropriate
                                 */
                                ret = 1;
                                goto no_kprobe;
                        }
                        p = __this_cpu_read(current_kprobe);
                        if (p->break_handler && p->break_handler(p, regs)) {
                                goto ss_probe;
                        }
                }
                goto no_kprobe;
        }

        p = get_kprobe(addr);
        if (!p) {
                if (*addr != BREAKPOINT_INSTRUCTION) {
                        /*
                         * PowerPC has multiple variants of the "trap"
                         * instruction. If the current instruction is a
                         * trap variant, it could belong to someone else
                         */
                        kprobe_opcode_t cur_insn = *addr;
                        if (is_trap(cur_insn))
                                goto no_kprobe;
                        /*
                         * The breakpoint instruction was removed right
                         * after we hit it.  Another cpu has removed
                         * either a probepoint or a debugger breakpoint
                         * at this address.  In either case, no further
                         * handling of this interrupt is appropriate.
                         */
                        ret = 1;
                }
                /* Not one of ours: let kernel handle it */
                goto no_kprobe;
        }

        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
        set_current_kprobe(p, regs, kcb);
        if (p->pre_handler && p->pre_handler(p, regs))
                /* handler has already set things up, so skip ss setup */
                return 1;

ss_probe:
        if (p->ainsn.boostable >= 0) {
                unsigned int insn = *p->ainsn.insn;

                /* regs->nip is also adjusted if emulate_step returns 1 */
                ret = emulate_step(regs, insn);
                if (ret > 0) {
                        /*
                         * Once this instruction has been boosted
                         * successfully, set the boostable flag
                         */
                        if (unlikely(p->ainsn.boostable == 0))
                                p->ainsn.boostable = 1;

                        if (p->post_handler)
                                p->post_handler(p, regs, 0);

                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                        reset_current_kprobe();
                        preempt_enable_no_resched();
                        return 1;
                } else if (ret < 0) {
                        /*
                         * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
                         * So, we should never get here... but, its still
                         * good to catch them, just in case...
                         */
                        printk("Can't step on instruction %x\n", insn);
                        BUG();
                } else if (ret == 0)
                        /* This instruction can't be boosted */
                        p->ainsn.boostable = -1;
        }
        prepare_singlestep(p, regs);
        kcb->kprobe_status = KPROBE_HIT_SS;
        return 1;

no_kprobe:
        preempt_enable_no_resched();
        return ret;
}

/*
 * Function return probe trampoline:
 *      - init_kprobes() establishes a probepoint here
 *      - When the probed function returns, this probe
 *              causes the handlers to fire
 */
asm(".global kretprobe_trampoline\n"
        ".type kretprobe_trampoline, @function\n"
        "kretprobe_trampoline:\n"
        "nop\n"
        "blr\n"
        ".size kretprobe_trampoline, .-kretprobe_trampoline\n");

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                                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;

        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 an multiple functions in the call path
         * have a return probe installed on them, and/or more than one return
         * 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;

                if (ri->rp && ri->rp->handler)
                        ri->rp->handler(ri, regs);

                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);
        regs->nip = orig_ret_address;
        /*
         * Make LR point to the orig_ret_address.
         * When the 'nop' inside the kretprobe_trampoline
         * is optimized, we can do a 'blr' after executing the
         * detour buffer code.
         */
        regs->link = orig_ret_address;

        reset_current_kprobe();
        kretprobe_hash_unlock(current, &flags);
        preempt_enable_no_resched();

        hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
                hlist_del(&ri->hlist);
                kfree(ri);
        }
        /*
         * By returning a non-zero value, we are telling
         * kprobe_handler() that we don't want the post_handler
         * to run (and have re-enabled preemption)
         */
        return 1;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "breakpoint"
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn.
 */
int __kprobes kprobe_post_handler(struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        if (!cur || user_mode(regs))
                return 0;

        /* make sure we got here for instruction we have a kprobe on */
        if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
                return 0;

        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                cur->post_handler(cur, regs, 0);
        }

        /* Adjust nip to after the single-stepped instruction */
        regs->nip = (unsigned long)cur->addr + 4;
        regs->msr |= kcb->kprobe_saved_msr;

        /*Restore back the original saved kprobes variables and continue. */
        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                goto out;
        }
        reset_current_kprobe();
out:
        preempt_enable_no_resched();

        /*
         * if somebody else is singlestepping across a probe point, msr
         * will have DE/SE set, in which case, continue the remaining processing
         * of do_debug, as if this is not a probe hit.
         */
        if (regs->msr & MSR_SINGLESTEP)
                return 0;

        return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        const struct exception_table_entry *entry;

        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 nip points back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                regs->nip = (unsigned long)cur->addr;
                regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
                regs->msr |= kcb->kprobe_saved_msr;
                if (kcb->kprobe_status == KPROBE_REENTER)
                        restore_previous_kprobe(kcb);
                else
                        reset_current_kprobe();
                preempt_enable_no_resched();
                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 first.
                 */
                if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
                        return 1;

                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.
                 */
                if ((entry = search_exception_tables(regs->nip)) != NULL) {
                        regs->nip = extable_fixup(entry);
                        return 1;
                }

                /*
                 * fixup_exception() could not handle it,
                 * Let do_page_fault() fix it.
                 */
                break;
        default:
                break;
        }
        return 0;
}

/*
 * Wrapper routine to for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                                       unsigned long val, void *data)
{
        return NOTIFY_DONE;
}

unsigned long arch_deref_entry_point(void *entry)
{
        return ppc_global_function_entry(entry);
}

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();

        memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

        /* setup return addr to the jprobe handler routine */
        regs->nip = arch_deref_entry_point(jp->entry);
#ifdef PPC64_ELF_ABI_v2
        regs->gpr[12] = (unsigned long)jp->entry;
#elif defined(PPC64_ELF_ABI_v1)
        regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
#endif

        return 1;
}

void __used __kprobes jprobe_return(void)
{
        asm volatile("trap" ::: "memory");
}

static void __used __kprobes jprobe_return_end(void)
{
};

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        /*
         * FIXME - we should ideally be validating that we got here 'cos
         * of the "trap" in jprobe_return() above, before restoring the
         * saved regs...
         */
        memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
        preempt_enable_no_resched();
        return 1;
}

static struct kprobe trampoline_p = {
        .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
        .pre_handler = trampoline_probe_handler
};

int __init arch_init_kprobes(void)
{
        return register_kprobe(&trampoline_p);
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
        if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
                return 1;

        return 0;
}