[S390] kprobes breaks BUG_ON

[linux-2.6/linux-loongson.git] / arch / s390 / 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, 2006
 *
 * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/stop_machine.h>
#include <asm/cacheflush.h>
#include <asm/kdebug.h>
#include <asm/sections.h>
#include <asm/uaccess.h>
#include <linux/module.h>

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

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        /* Make sure the probe isn't going on a difficult instruction */
        if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
                return -EINVAL;

        if ((unsigned long)p->addr & 0x01) {
                printk("Attempt to register kprobe at an unaligned address\n");
                return -EINVAL;
                }

        /* Use the get_insn_slot() facility for correctness */
        if (!(p->ainsn.insn = get_insn_slot()))
                return -ENOMEM;

        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

        get_instruction_type(&p->ainsn);
        p->opcode = *p->addr;
        return 0;
}

int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
{
        switch (*(__u8 *) instruction) {
        case 0x0c:      /* bassm */
        case 0x0b:      /* bsm   */
        case 0x83:      /* diag  */
        case 0x44:      /* ex    */
                return -EINVAL;
        }
        switch (*(__u16 *) instruction) {
        case 0x0101:    /* pr    */
        case 0xb25a:    /* bsa   */
        case 0xb240:    /* bakr  */
        case 0xb258:    /* bsg   */
        case 0xb218:    /* pc    */
        case 0xb228:    /* pt    */
                return -EINVAL;
        }
        return 0;
}

void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
{
        /* default fixup method */
        ainsn->fixup = FIXUP_PSW_NORMAL;

        /* save r1 operand */
        ainsn->reg = (*ainsn->insn & 0xf0) >> 4;

        /* save the instruction length (pop 5-5) in bytes */
        switch (*(__u8 *) (ainsn->insn) >> 4) {
        case 0:
                ainsn->ilen = 2;
                break;
        case 1:
        case 2:
                ainsn->ilen = 4;
                break;
        case 3:
                ainsn->ilen = 6;
                break;
        }

        switch (*(__u8 *) ainsn->insn) {
        case 0x05:      /* balr */
        case 0x0d:      /* basr */
                ainsn->fixup = FIXUP_RETURN_REGISTER;
                /* if r2 = 0, no branch will be taken */
                if ((*ainsn->insn & 0x0f) == 0)
                        ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
                break;
        case 0x06:      /* bctr */
        case 0x07:      /* bcr  */
                ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
                break;
        case 0x45:      /* bal  */
        case 0x4d:      /* bas  */
                ainsn->fixup = FIXUP_RETURN_REGISTER;
                break;
        case 0x47:      /* bc   */
        case 0x46:      /* bct  */
        case 0x86:      /* bxh  */
        case 0x87:      /* bxle */
                ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
                break;
        case 0x82:      /* lpsw */
                ainsn->fixup = FIXUP_NOT_REQUIRED;
                break;
        case 0xb2:      /* lpswe */
                if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
                        ainsn->fixup = FIXUP_NOT_REQUIRED;
                }
                break;
        case 0xa7:      /* bras */
                if ((*ainsn->insn & 0x0f) == 0x05) {
                        ainsn->fixup |= FIXUP_RETURN_REGISTER;
                }
                break;
        case 0xc0:
                if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
                        || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
                ainsn->fixup |= FIXUP_RETURN_REGISTER;
                break;
        case 0xeb:
                if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
                        *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
                        ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
                }
                break;
        case 0xe3:      /* bctg */
                if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
                        ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
                }
                break;
        }
}

static int __kprobes swap_instruction(void *aref)
{
        struct ins_replace_args *args = aref;
        u32 *addr;
        u32 instr;
        int err = -EFAULT;

        /*
         * Text segment is read-only, hence we use stura to bypass dynamic
         * address translation to exchange the instruction. Since stura
         * always operates on four bytes, but we only want to exchange two
         * bytes do some calculations to get things right. In addition we
         * shall not cross any page boundaries (vmalloc area!) when writing
         * the new instruction.
         */
        addr = (u32 *)ALIGN((unsigned long)args->ptr, 4);
        if ((unsigned long)args->ptr & 2)
                instr = ((*addr) & 0xffff0000) | args->new;
        else
                instr = ((*addr) & 0x0000ffff) | args->new << 16;

        asm volatile(
                "       lra     %1,0(%1)\n"
                "0:     stura   %2,%1\n"
                "1:     la      %0,0\n"
                "2:\n"
                EX_TABLE(0b,2b)
                : "+d" (err)
                : "a" (addr), "d" (instr)
                : "memory", "cc");

        return err;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long status = kcb->kprobe_status;
        struct ins_replace_args args;

        args.ptr = p->addr;
        args.old = p->opcode;
        args.new = BREAKPOINT_INSTRUCTION;

        kcb->kprobe_status = KPROBE_SWAP_INST;
        stop_machine_run(swap_instruction, &args, NR_CPUS);
        kcb->kprobe_status = status;
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long status = kcb->kprobe_status;
        struct ins_replace_args args;

        args.ptr = p->addr;
        args.old = BREAKPOINT_INSTRUCTION;
        args.new = p->opcode;

        kcb->kprobe_status = KPROBE_SWAP_INST;
        stop_machine_run(swap_instruction, &args, NR_CPUS);
        kcb->kprobe_status = status;
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        mutex_lock(&kprobe_mutex);
        free_insn_slot(p->ainsn.insn, 0);
        mutex_unlock(&kprobe_mutex);
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        per_cr_bits kprobe_per_regs[1];

        memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
        regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;

        /* Set up the per control reg info, will pass to lctl */
        kprobe_per_regs[0].em_instruction_fetch = 1;
        kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
        kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;

        /* Set the PER control regs, turns on single step for this address */
        __ctl_load(kprobe_per_regs, 9, 11);
        regs->psw.mask |= PSW_MASK_PER;
        regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
}

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.kprobe_saved_imask = kcb->kprobe_saved_imask;
        memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
                                        sizeof(kcb->kprobe_saved_ctl));
}

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;
        kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
        memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
                                        sizeof(kcb->kprobe_saved_ctl));
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                                struct kprobe_ctlblk *kcb)
{
        __get_cpu_var(current_kprobe) = p;
        /* Save the interrupt and per flags */
        kcb->kprobe_saved_imask = regs->psw.mask &
            (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
        /* Save the control regs that govern PER */
        __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
                                        struct pt_regs *regs)
{
        struct kretprobe_instance *ri;

        if ((ri = get_free_rp_inst(rp)) != NULL) {
                ri->rp = rp;
                ri->task = current;
                ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];

                /* Replace the return addr with trampoline addr */
                regs->gprs[14] = (unsigned long)&kretprobe_trampoline;

                add_rp_inst(ri);
        } else {
                rp->nmissed++;
        }
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        int ret = 0;
        unsigned long *addr = (unsigned long *)
                ((regs->psw.addr & PSW_ADDR_INSN) - 2);
        struct kprobe_ctlblk *kcb;

        /*
         * 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) {
                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
                            *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
                                regs->psw.mask &= ~PSW_MASK_PER;
                                regs->psw.mask |= kcb->kprobe_saved_imask;
                                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)
                /*
                 * No kprobe at this address. The fault has not been
                 * caused by a kprobe breakpoint. The race of breakpoint
                 * vs. kprobe remove does not exist because on s390 we
                 * use stop_machine_run to arm/disarm the breakpoints.
                 */
                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:
        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
 */
void kretprobe_trampoline_holder(void)
{
        asm volatile(".global kretprobe_trampoline\n"
                     "kretprobe_trampoline: bcr 0,0\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 *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 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)
                        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;
                }
        }
        BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
        regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;

        reset_current_kprobe();
        spin_unlock_irqrestore(&kretprobe_lock, flags);
        preempt_enable_no_resched();

        hlist_for_each_entry_safe(ri, node, 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.
 */
static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        regs->psw.addr &= PSW_ADDR_INSN;

        if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
                regs->psw.addr = (unsigned long)p->addr +
                                ((unsigned long)regs->psw.addr -
                                 (unsigned long)p->ainsn.insn);

        if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
                if ((unsigned long)regs->psw.addr -
                    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
                        regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;

        if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
                regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
                                                (regs->gprs[p->ainsn.reg] -
                                                (unsigned long)p->ainsn.insn))
                                                | PSW_ADDR_AMODE;

        regs->psw.addr |= PSW_ADDR_AMODE;
        /* turn off PER mode */
        regs->psw.mask &= ~PSW_MASK_PER;
        /* Restore the original per control regs */
        __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
        regs->psw.mask |= kcb->kprobe_saved_imask;
}

static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        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);
        }

        resume_execution(cur, regs);

        /*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, psw mask
         * will have PER set, in which case, continue the remaining processing
         * of do_single_step, as if this is not a probe hit.
         */
        if (regs->psw.mask & PSW_MASK_PER) {
                return 0;
        }

        return 1;
}

static 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_SWAP_INST:
                /* We are here because the instruction replacement failed */
                return 0;
        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->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
                regs->psw.mask &= ~PSW_MASK_PER;
                regs->psw.mask |= kcb->kprobe_saved_imask;
                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 accouting
                 * 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.
                 */
                entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
                if (entry) {
                        regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
                        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 die_args *args = (struct die_args *)data;
        int ret = NOTIFY_DONE;

        switch (val) {
        case DIE_BPT:
                if (kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_SSTEP:
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_TRAP:
        case DIE_PAGE_FAULT:
                /* kprobe_running() needs smp_processor_id() */
                preempt_disable();
                if (kprobe_running() &&
                    kprobe_fault_handler(args->regs, args->trapnr))
                        ret = NOTIFY_STOP;
                preempt_enable();
                break;
        default:
                break;
        }
        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();

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

        /* setup return addr to the jprobe handler routine */
        regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;

        /* r14 is the function return address */
        kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
        /* r15 is the stack pointer */
        kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
        addr = (unsigned long)kcb->jprobe_saved_r15;

        memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
               MIN_STACK_SIZE(addr));
        return 1;
}

void __kprobes jprobe_return(void)
{
        asm volatile(".word 0x0002");
}

void __kprobes jprobe_return_end(void)
{
        asm volatile("bcr 0,0");
}

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

        /* Put the regs back */
        memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
        /* put the stack back */
        memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
               MIN_STACK_SIZE(stack_addr));
        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);
}