kprobes.c

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/*
 *  Kernel Probes (KProbes)
 *  arch/i386/kernel/kprobes.c
 *
 * 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 <[e-mail]> Kernel
 *		Probes initial implementation ( includes contributions from
 *		Rusty Russell).
 * 2004-July	Suparna Bhattacharya <[e-mail]> added jumper probes
 *		interface to access function arguments.
 * 2005-May	Hien Nguyen <[e-mail]>, Jim Keniston
 *		<[e-mail]> and Prasanna S Panchamukhi
 *		<[e-mail]> added function-return probes.
 */

#include <linux/config.h>
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <asm/cacheflush.h>
#include <asm/kdebug.h>
#include <asm/desc.h>
#include <asm/uaccess.h>

void jprobe_return_end(void);

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

/* insert a jmp code */
static __always_inline void set_jmp_op(void *from, void *to)
{
	struct __arch_jmp_op {
		char op;
		long raddr;
	} __attribute__((packed)) *jop;
	jop = (struct __arch_jmp_op *)from;
	jop->raddr = (long)(to) - ((long)(from) + 5);
	jop->op = RELATIVEJUMP_INSTRUCTION;
}

/*
 * returns non-zero if opcodes can be boosted.
 */
static __always_inline int can_boost(kprobe_opcode_t opcode)
{
	switch (opcode & 0xf0 ) {
	case 0x70:
		return 0; /* can't boost conditional jump */
	case 0x90:
		/* can't boost call and pushf */
		return opcode != 0x9a && opcode != 0x9c;
	case 0xc0:
		/* can't boost undefined opcodes and soft-interruptions */
		return (0xc1 < opcode && opcode < 0xc6) ||
			(0xc7 < opcode && opcode < 0xcc) || opcode == 0xcf;
	case 0xd0:
		/* can boost AA* and XLAT */
		return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
	case 0xe0:
		/* can boost in/out and (may be) jmps */
		return (0xe3 < opcode && opcode != 0xe8);
	case 0xf0:
		/* clear and set flags can be boost */
		return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
	default:
		/* currently, can't boost 2 bytes opcodes */
		return opcode != 0x0f;
	}
}


/*
 * returns non-zero if opcode modifies the interrupt flag.
 */
static int __kprobes is_IF_modifier(kprobe_opcode_t opcode)
{
	switch (opcode) {
	case 0xfa:		/* cli */
	case 0xfb:		/* sti */
	case 0xcf:		/* iret/iretd */
	case 0x9d:		/* popf/popfd */
		return 1;
	}
	return 0;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	/* insn: must be on special executable page on i386. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
		return -ENOMEM;

	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
	p->opcode = *p->addr;
	if (can_boost(p->opcode)) {
		p->ainsn.boostable = 0;
	} else {
		p->ainsn.boostable = -1;
	}
	return 0;
}

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)
{
	mutex_lock(&kprobe_mutex);
	free_insn_slot(p->ainsn.insn);
	mutex_unlock(&kprobe_mutex);
}

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.old_eflags = kcb->kprobe_old_eflags;
	kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
}

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_old_eflags = kcb->prev_kprobe.old_eflags;
	kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
				struct kprobe_ctlblk *kcb)
{
	__get_cpu_var(current_kprobe) = p;
	kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
		= (regs->eflags & (TF_MASK | IF_MASK));
	if (is_IF_modifier(p->opcode))
		kcb->kprobe_saved_eflags &= ~IF_MASK;
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
	regs->eflags |= TF_MASK;
	regs->eflags &= ~IF_MASK;
	/*single step inline if the instruction is an int3*/
	if (p->opcode == BREAKPOINT_INSTRUCTION)
		regs->eip = (unsigned long)p->addr;
	else
		regs->eip = (unsigned long)p->ainsn.insn;
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
				      struct pt_regs *regs)
{
	unsigned long *sara = (unsigned long *)&regs->esp;
        struct kretprobe_instance *ri;

        if ((ri = get_free_rp_inst(rp)) != NULL) {
                ri->rp = rp;
                ri->task = current;
		ri->ret_addr = (kprobe_opcode_t *) *sara;

		/* Replace the return addr with trampoline addr */
		*sara = (unsigned long) &kretprobe_trampoline;

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

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled thorough out this function.
 */
static int __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p;
	int ret = 0;
	kprobe_opcode_t *addr;
	struct kprobe_ctlblk *kcb;
#ifdef CONFIG_PREEMPT
	unsigned pre_preempt_count = preempt_count();
#endif /* CONFIG_PREEMPT */

	addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));

	/*
	 * 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->eflags &= ~TF_MASK;
				regs->eflags |= kcb->kprobe_saved_eflags;
				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 {
			if (*addr != BREAKPOINT_INSTRUCTION) {
			/* The breakpoint instruction was removed by
			 * another cpu right after we hit, no further
			 * handling of this interrupt is appropriate
			 */
				regs->eip -= sizeof(kprobe_opcode_t);
				ret = 1;
				goto no_kprobe;
			}
			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) {
		if (*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.
			 * Back up over the (now missing) int3 and run
			 * the original instruction.
			 */
			regs->eip -= sizeof(kprobe_opcode_t);
			ret = 1;
		}
		/* Not one of ours: let kernel handle it */
		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;

	if (p->ainsn.boostable == 1 &&
#ifdef CONFIG_PREEMPT
	    !(pre_preempt_count) && /*
				       * This enables booster when the direct
				       * execution path aren't preempted.
				       */
#endif /* CONFIG_PREEMPT */
	    !p->post_handler && !p->break_handler ) {
		/* Boost up -- we can execute copied instructions directly */
		reset_current_kprobe();
		regs->eip = (unsigned long)p->ainsn.insn;
		preempt_enable_no_resched();
		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.
 */
 void __kprobes kretprobe_trampoline_holder(void)
 {
	asm volatile ( ".global kretprobe_trampoline\n"
 			"kretprobe_trampoline: \n"
			"	pushf\n"
			/* skip cs, eip, orig_eax, es, ds */
			"	subl $20, %esp\n"
			"	pushl %eax\n"
			"	pushl %ebp\n"
			"	pushl %edi\n"
			"	pushl %esi\n"
			"	pushl %edx\n"
			"	pushl %ecx\n"
			"	pushl %ebx\n"
			"	movl %esp, %eax\n"
			"	call trampoline_handler\n"
			/* move eflags to cs */
			"	movl 48(%esp), %edx\n"
			"	movl %edx, 44(%esp)\n"
			/* save true return address on eflags */
			"	movl %eax, 48(%esp)\n"
			"	popl %ebx\n"
			"	popl %ecx\n"
			"	popl %edx\n"
			"	popl %esi\n"
			"	popl %edi\n"
			"	popl %ebp\n"
			"	popl %eax\n"
			/* skip eip, orig_eax, es, ds */
			"	addl $16, %esp\n"
			"	popf\n"
			"	ret\n");
}

/*
 * Called from kretprobe_trampoline