sh: kprobes: Fix up race against probe point removal.

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / arch / sh / kernel / kprobes.c

/*
 * Kernel probes (kprobes) for SuperH
 *
 * Copyright (C) 2007 Chris Smith <chris.smith@st.com>
 * Copyright (C) 2006 Lineo Solutions, Inc.
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/kdebug.h>
#include <asm/cacheflush.h>
#include <asm/uaccess.h>

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

static struct kprobe saved_current_opcode;
static struct kprobe saved_next_opcode;
static struct kprobe saved_next_opcode2;

#define OPCODE_JMP(x)   (((x) & 0xF0FF) == 0x402b)
#define OPCODE_JSR(x)   (((x) & 0xF0FF) == 0x400b)
#define OPCODE_BRA(x)   (((x) & 0xF000) == 0xa000)
#define OPCODE_BRAF(x)  (((x) & 0xF0FF) == 0x0023)
#define OPCODE_BSR(x)   (((x) & 0xF000) == 0xb000)
#define OPCODE_BSRF(x)  (((x) & 0xF0FF) == 0x0003)

#define OPCODE_BF_S(x)  (((x) & 0xFF00) == 0x8f00)
#define OPCODE_BT_S(x)  (((x) & 0xFF00) == 0x8d00)

#define OPCODE_BF(x)    (((x) & 0xFF00) == 0x8b00)
#define OPCODE_BT(x)    (((x) & 0xFF00) == 0x8900)

#define OPCODE_RTS(x)   (((x) & 0x000F) == 0x000b)
#define OPCODE_RTE(x)   (((x) & 0xFFFF) == 0x002b)

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

        if (OPCODE_RTE(opcode))
                return -EFAULT; /* Bad breakpoint */

        p->opcode = opcode;

        return 0;
}

void __kprobes arch_copy_kprobe(struct kprobe *p)
{
        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
        p->opcode = *p->addr;
}

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));
}

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

        return 0;
}

/**
 * If an illegal slot instruction exception occurs for an address
 * containing a kprobe, remove the probe.
 *
 * Returns 0 if the exception was handled successfully, 1 otherwise.
 */
int __kprobes kprobe_handle_illslot(unsigned long pc)
{
        struct kprobe *p = get_kprobe((kprobe_opcode_t *) pc + 1);

        if (p != NULL) {
                printk("Warning: removing kprobe from delay slot: 0x%.8x\n",
                       (unsigned int)pc + 2);
                unregister_kprobe(p);
                return 0;
        }

        return 1;
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        if (saved_next_opcode.addr != 0x0) {
                arch_disarm_kprobe(p);
                arch_disarm_kprobe(&saved_next_opcode);
                saved_next_opcode.addr = 0x0;
                saved_next_opcode.opcode = 0x0;

                if (saved_next_opcode2.addr != 0x0) {
                        arch_disarm_kprobe(&saved_next_opcode2);
                        saved_next_opcode2.addr = 0x0;
                        saved_next_opcode2.opcode = 0x0;
                }
        }
}

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

static inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
        kcb->kprobe_status = kcb->prev_kprobe.status;
}

static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                      struct kprobe_ctlblk *kcb)
{
        __get_cpu_var(current_kprobe) = p;
}

/*
 * Singlestep is implemented by disabling the current kprobe and setting one
 * on the next instruction, following branches. Two probes are set if the
 * branch is conditional.
 */
static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        kprobe_opcode_t *addr = NULL;
        saved_current_opcode.addr = (kprobe_opcode_t *) (regs->pc);
        addr = saved_current_opcode.addr;

        if (p != NULL) {
                arch_disarm_kprobe(p);

                if (OPCODE_JSR(p->opcode) || OPCODE_JMP(p->opcode)) {
                        unsigned int reg_nr = ((p->opcode >> 8) & 0x000F);
                        saved_next_opcode.addr =
                            (kprobe_opcode_t *) regs->regs[reg_nr];
                } else if (OPCODE_BRA(p->opcode) || OPCODE_BSR(p->opcode)) {
                        unsigned long disp = (p->opcode & 0x0FFF);
                        saved_next_opcode.addr =
                            (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);

                } else if (OPCODE_BRAF(p->opcode) || OPCODE_BSRF(p->opcode)) {
                        unsigned int reg_nr = ((p->opcode >> 8) & 0x000F);
                        saved_next_opcode.addr =
                            (kprobe_opcode_t *) (regs->pc + 4 +
                                                 regs->regs[reg_nr]);

                } else if (OPCODE_RTS(p->opcode)) {
                        saved_next_opcode.addr = (kprobe_opcode_t *) regs->pr;

                } else if (OPCODE_BF(p->opcode) || OPCODE_BT(p->opcode)) {
                        unsigned long disp = (p->opcode & 0x00FF);
                        /* case 1 */
                        saved_next_opcode.addr = p->addr + 1;
                        /* case 2 */
                        saved_next_opcode2.addr =
                            (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);
                        saved_next_opcode2.opcode = *(saved_next_opcode2.addr);
                        arch_arm_kprobe(&saved_next_opcode2);

                } else if (OPCODE_BF_S(p->opcode) || OPCODE_BT_S(p->opcode)) {
                        unsigned long disp = (p->opcode & 0x00FF);
                        /* case 1 */
                        saved_next_opcode.addr = p->addr + 2;
                        /* case 2 */
                        saved_next_opcode2.addr =
                            (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);
                        saved_next_opcode2.opcode = *(saved_next_opcode2.addr);
                        arch_arm_kprobe(&saved_next_opcode2);

                } else {
                        saved_next_opcode.addr = p->addr + 1;
                }

                saved_next_opcode.opcode = *(saved_next_opcode.addr);
                arch_arm_kprobe(&saved_next_opcode);
        }
}

/* 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->pr;

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

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        int ret = 0;
        kprobe_opcode_t *addr = NULL;
        struct kprobe_ctlblk *kcb;

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

        addr = (kprobe_opcode_t *) (regs->pc);

        /* Check we're not actually recursing */
        if (kprobe_running()) {
                p = get_kprobe(addr);
                if (p) {
                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
                            *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
                                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);
                        kprobes_inc_nmissed_count(p);
                        prepare_singlestep(p, regs);
                        kcb->kprobe_status = KPROBE_REENTER;
                        return 1;
                } else {
                        p = __get_cpu_var(current_kprobe);
                        if (p->break_handler && p->break_handler(p, regs)) {
                                goto ss_probe;
                        }
                }
                goto no_kprobe;
        }

        p = get_kprobe(addr);
        if (!p) {
                /* Not one of ours: let kernel handle it */
                if (*(kprobe_opcode_t *)addr != BREAKPOINT_INSTRUCTION) {
                        /*
                         * 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;
                }

                goto no_kprobe;
        }

        set_current_kprobe(p, regs, kcb);
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;

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

      ss_probe:
        prepare_singlestep(p, regs);
        kcb->kprobe_status = KPROBE_HIT_SS;
        return 1;

      no_kprobe:
        preempt_enable_no_resched();
        return ret;
}

/*
 * For function-return probes, init_kprobes() establishes a probepoint
 * here. When a retprobed function returns, this probe is hit and
 * trampoline_probe_handler() runs, calling the kretprobe's handler.
 */
static void __used kretprobe_trampoline_holder(void)
{
        asm volatile ("kretprobe_trampoline: \n" "nop\n");
}

/*
 * Called when we hit the probe point at kretprobe_trampoline
 */
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 *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 then 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, 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;
                        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);

        regs->pc = orig_ret_address;
        kretprobe_hash_unlock(current, &flags);

        preempt_enable_no_resched();

        hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
                hlist_del(&ri->hlist);
                kfree(ri);
        }

        return orig_ret_address;
}

static inline int post_kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        kprobe_opcode_t *addr = NULL;
        struct kprobe *p = NULL;

        if (!cur)
                return 0;

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

        if (saved_next_opcode.addr != 0x0) {
                arch_disarm_kprobe(&saved_next_opcode);
                saved_next_opcode.addr = 0x0;
                saved_next_opcode.opcode = 0x0;

                addr = saved_current_opcode.addr;
                saved_current_opcode.addr = 0x0;

                p = get_kprobe(addr);
                arch_arm_kprobe(p);

                if (saved_next_opcode2.addr != 0x0) {
                        arch_disarm_kprobe(&saved_next_opcode2);
                        saved_next_opcode2.addr = 0x0;
                        saved_next_opcode2.opcode = 0x0;
                }
        }

        /*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();

        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, point the pc back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                regs->pc = (unsigned long)cur->addr;
                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->pc)) != NULL) {
                        regs->pc = entry->fixup;
                        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)
{
        struct kprobe *p = NULL;
        struct die_args *args = (struct die_args *)data;
        int ret = NOTIFY_DONE;
        kprobe_opcode_t *addr = NULL;
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        addr = (kprobe_opcode_t *) (args->regs->pc);
        if (val == DIE_TRAP) {
                if (!kprobe_running()) {
                        if (kprobe_handler(args->regs)) {
                                ret = NOTIFY_STOP;
                        } else {
                                /* Not a kprobe trap */
                                ret = NOTIFY_DONE;
                        }
                } else {
                        p = get_kprobe(addr);
                        if ((kcb->kprobe_status == KPROBE_HIT_SS) ||
                            (kcb->kprobe_status == KPROBE_REENTER)) {
                                if (post_kprobe_handler(args->regs))
                                        ret = NOTIFY_STOP;
                        } else {
                                if (kprobe_handler(args->regs)) {
                                        ret = NOTIFY_STOP;
                                } else {
                                        p = __get_cpu_var(current_kprobe);
                                        if (p->break_handler
                                            && p->break_handler(p, args->regs))
                                                ret = NOTIFY_STOP;
                                }
                        }
                }
        }

        return ret;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct jprobe *jp = container_of(p, struct jprobe, kp);
        unsigned long addr;
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        kcb->jprobe_saved_regs = *regs;
        kcb->jprobe_saved_r15 = regs->regs[15];
        addr = kcb->jprobe_saved_r15;

        /*
         * TBD: As Linus pointed out, gcc assumes that the callee
         * owns the argument space and could overwrite it, e.g.
         * tailcall optimization. So, to be absolutely safe
         * we also save and restore enough stack bytes to cover
         * the argument area.
         */
        memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
               MIN_STACK_SIZE(addr));

        regs->pc = (unsigned long)(jp->entry);

        return 1;
}

void __kprobes jprobe_return(void)
{
        asm volatile ("trapa #0x3a\n\t" "jprobe_return_end:\n\t" "nop\n\t");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        u8 *addr = (u8 *) regs->pc;
        unsigned long stack_addr = kcb->jprobe_saved_r15;

        if ((addr >= (u8 *) jprobe_return)
            && (addr <= (u8 *) jprobe_return_end)) {
                *regs = kcb->jprobe_saved_regs;

                memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
                       MIN_STACK_SIZE(stack_addr));

                kcb->kprobe_status = KPROBE_HIT_SS;
                preempt_enable_no_resched();
                return 1;
        }
        return 0;
}

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

int __init arch_init_kprobes(void)
{
        saved_next_opcode.addr = 0x0;
        saved_next_opcode.opcode = 0x0;

        saved_current_opcode.addr = 0x0;
        saved_current_opcode.opcode = 0x0;

        saved_next_opcode2.addr = 0x0;
        saved_next_opcode2.opcode = 0x0;

        return register_kprobe(&trampoline_p);
}