/*
* 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 <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.
*/
#include <linux/config.h>
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/spinlock.h>
#include <linux/preempt.h>
#include <asm/kdebug.h>
#include <asm/desc.h>
/* kprobe_status settings */
#define KPROBE_HIT_ACTIVE 0x00000001
#define KPROBE_HIT_SS 0x00000002
static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_old_eflags, kprobe_saved_eflags;
static struct pt_regs jprobe_saved_regs;
static long *jprobe_saved_esp;
/* copy of the kernel stack at the probe fire time */
static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
void jprobe_return_end(void);
/*
* returns non-zero if opcode modifies the interrupt flag.
*/
static inline int 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 arch_prepare_kprobe(struct kprobe *p)
{
return 0;
}
void arch_copy_kprobe(struct kprobe *p)
{
memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
}
void arch_remove_kprobe(struct kprobe *p)
{
}
static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
{
*p->addr = p->opcode;
regs->eip = (unsigned long)p->addr;
}
static inline void 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;
}
/*
* Interrupts are disabled on entry as trap3 is an interrupt gate and they
* remain disabled thorough out this function.
*/
static int kprobe_handler(struct pt_regs *regs)
{
struct kprobe *p;
int ret = 0;
kprobe_opcode_t *addr = NULL;
unsigned long *lp;
/* We're in an interrupt, but this is clear and BUG()-safe. */
preempt_disable();
/* Check if the application is using LDT entry for its code segment and
* calculate the address by reading the base address from the LDT entry.
*/
if ((regs->xcs & 4) && (current->mm)) {
lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8)
+ (char *) current->mm->context.ldt);
addr = (kprobe_opcode_t *) (get_desc_base(lp) + regs->eip -
sizeof(kprobe_opcode_t));
} else {
addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
}
/* Check we're not actually recursing */
if (kprobe_running()) {
/* We *are* holding lock here, so this is safe.
Disarm the probe we just hit, and ignore it. */
p = get_kprobe(addr);
if (p) {
if (kprobe_status == KPROBE_HIT_SS) {
regs->eflags &= ~TF_MASK;
regs->eflags |= kprobe_saved_eflags;
unlock_kprobes();
goto no_kprobe;
}
disarm_kprobe(p, regs);
ret = 1;
} else {
p = current_kprobe;
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;
}
}
/* If it's not ours, can't be delete race, (we hold lock). */
goto no_kprobe;
}
lock_kprobes();
p = get_kprobe(addr);
if (!p) {
unlock_kprobes();
if (regs->eflags & VM_MASK) {
/* We are in virtual-8086 mode. Return 0 */
goto no_kprobe;
}
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.
*/
ret = 1;
}
/* Not one of ours: let kernel handle it */
goto no_kprobe;
}
kprobe_status = KPROBE_HIT_ACTIVE;
current_kprobe = p;
kprobe_saved_eflags = kprobe_old_eflags
= (regs->eflags & (TF_MASK | IF_MASK));
if (is_IF_modifier(p->opcode))
kprobe_saved_eflags &= ~IF_MASK;
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);
kprobe_status = KPROBE_HIT_SS;
return 1;
no_kprobe:
preempt_enable_no_resched();
return ret;
}
/*
* Called after single-stepping. p->addr is the address of the
* instruction whose first byte has been replaced by the "int 3"
* 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.
*
* This function prepares to return from the post-single-step
* interrupt. We have to fix up the stack as follows:
*
* 0) Except in the case of absolute or indirect jump or call instructions,
* the new eip is relative to the copied instruction. We need to make
* it relative to the original instruction.
*
* 1) If the single-stepped instruction was pushfl, then the TF and IF
* flags are set in the just-pushed eflags, and may need to be cleared.
*
* 2) If the single-stepped instruction was a call, the return address
* that is atop the stack is the address following the copied instruction.
* We need to make it the address following the original instruction.
*/
static void resume_execution(struct kprobe *p, struct pt_regs *regs)
{
unsigned long *tos = (unsigned long *)®s->esp;
unsigned long next_eip = 0;
unsigned long copy_eip = (unsigned long)&p->ainsn.insn;
unsigned long orig_eip = (unsigned long)p->addr;
switch (p->ainsn.insn[0]) {
case 0x9c: /* pushfl */
*tos &= ~(TF_MASK | IF_MASK);
*tos |= kprobe_old_eflags;
break;
case 0xc3: /* ret/lret */
case 0xcb:
case 0xc2:
case 0xca:
regs->eflags &= ~TF_MASK;
/* eip is already adjusted, no more changes required*/
return;
case 0xe8: /* call relative - Fix return addr */
*tos = orig_eip + (*tos - copy_eip);
break;
case 0xff:
if ((p->ainsn.insn[1] & 0x30) == 0x10) {
/* call absolute, indirect */
/* Fix return addr; eip is correct. */
next_eip = regs->eip;
*tos = orig_eip + (*tos - copy_eip);
} else if (((p->ainsn.insn[1] & 0x31) == 0x20) || /* jmp near, absolute indirect */
((p->ainsn.insn[1] & 0x31) == 0x21)) { /* jmp far, absolute indirect */
/* eip is correct. */
next_eip = regs->eip;
}
break;
case 0xea: /* jmp absolute -- eip is correct */
next_eip = regs->eip;
break;
default:
break;
}
regs->eflags &= ~TF_MASK;
if (next_eip) {
regs->eip = next_eip;
} else {
regs->eip = orig_eip + (regs->eip - copy_eip);
}
}
/*
* Interrupts are disabled on entry as trap1 is an interrupt gate and they
* remain disabled thoroughout this function. And we hold kprobe lock.
*/
static inline int post_kprobe_handler(struct pt_regs *regs)
{
if (!kprobe_running())
return 0;
if (current_kprobe->post_handler)
current_kprobe->post_handler(current_kprobe, regs, 0);
resume_execution(current_kprobe, regs);
regs->eflags |= kprobe_saved_eflags;
unlock_kprobes();
preempt_enable_no_resched();
/*
* if somebody else is singlestepping across a probe point, eflags
* will have TF set, in which case, continue the remaining processing
* of do_debug, as if this is not a probe hit.
*/
if (regs->eflags & TF_MASK)
return 0;
return 1;
}
/* Interrupts disabled, kprobe_lock held. */
static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
if (current_kprobe->fault_handler
&& current_kprobe->fault_handler(current_kprobe, regs, trapnr))
return 1;
if (kprobe_status & KPROBE_HIT_SS) {
resume_execution(current_kprobe, regs);
regs->eflags |= kprobe_old_eflags;
unlock_kprobes();
preempt_enable_no_resched();
}
return 0;
}
/*
* Wrapper routine to for handling exceptions.
*/
int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
void *data)
{
struct die_args *args = (struct die_args *)data;
switch (val) {
case DIE_INT3:
if (kprobe_handler(args->regs))
return NOTIFY_STOP;
break;
case DIE_DEBUG:
if (post_kprobe_handler(args->regs))
return NOTIFY_STOP;
break;
case DIE_GPF:
if (kprobe_running() &&
kprobe_fault_handler(args->regs, args->trapnr))
return NOTIFY_STOP;
break;
case DIE_PAGE_FAULT:
if (kprobe_running() &&
kprobe_fault_handler(args->regs, args->trapnr))
return NOTIFY_STOP;
break;
default:
break;
}
return NOTIFY_DONE;
}
int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
struct jprobe *jp = container_of(p, struct jprobe, kp);
unsigned long addr;
jprobe_saved_regs = *regs;
jprobe_saved_esp = ®s->esp;
addr = (unsigned long)jprobe_saved_esp;
/*
* 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(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr));
regs->eflags &= ~IF_MASK;
regs->eip = (unsigned long)(jp->entry);
return 1;
}
void jprobe_return(void)
{
preempt_enable_no_resched();
asm volatile (" xchgl %%ebx,%%esp \n"
" int3 \n"
" .globl jprobe_return_end \n"
" jprobe_return_end: \n"
" nop \n"::"b"
(jprobe_saved_esp):"memory");
}
int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
u8 *addr = (u8 *) (regs->eip - 1);
unsigned long stack_addr = (unsigned long)jprobe_saved_esp;
struct jprobe *jp = container_of(p, struct jprobe, kp);
if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
if (®s->esp != jprobe_saved_esp) {
struct pt_regs *saved_regs =
container_of(jprobe_saved_esp, struct pt_regs, esp);
printk("current esp %p does not match saved esp %p\n",
®s->esp, jprobe_saved_esp);
printk("Saved registers for jprobe %p\n", jp);
show_registers(saved_regs);
printk("Current registers\n");
show_registers(regs);
BUG();
}
*regs = jprobe_saved_regs;
memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack,
MIN_STACK_SIZE(stack_addr));
return 1;
}
return 0;
}
