/*
* Kernel Probes (KProbes)
* arch/x86_64/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.
* 2004-Oct Jim Keniston <kenistoj@us.ibm.com> and Prasanna S Panchamukhi
* <prasanna@in.ibm.com> adapted for x86_64
* 2005-Mar Roland McGrath <roland@redhat.com>
* Fixed to handle %rip-relative addressing mode correctly.
* 2005-May Rusty Lynch <rusty.lynch@intel.com>
* Added function return probes functionality
*/
#include <linux/config.h>
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/preempt.h>
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include <asm/pgtable.h>
#include <asm/kdebug.h>
static DECLARE_MUTEX(kprobe_mutex);
static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
static struct kprobe *kprobe_prev;
static unsigned long kprobe_status_prev, kprobe_old_rflags_prev, kprobe_saved_rflags_prev;
static struct pt_regs jprobe_saved_regs;
static long *jprobe_saved_rsp;
static kprobe_opcode_t *get_insn_slot(void);
static void free_insn_slot(kprobe_opcode_t *slot);
void jprobe_return_end(void);
/* copy of the kernel stack at the probe fire time */
static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
/*
* returns non-zero if opcode modifies the interrupt flag.
*/
static inline int is_IF_modifier(kprobe_opcode_t *insn)
{
switch (*insn) {
case 0xfa: /* cli */
case 0xfb: /* sti */
case 0xcf: /* iret/iretd */
case 0x9d: /* popf/popfd */
return 1;
}
if (*insn >= 0x40 && *insn <= 0x4f && *++insn == 0xcf)
return 1;
return 0;
}
int arch_prepare_kprobe(struct kprobe *p)
{
/* insn: must be on special executable page on x86_64. */
up(&kprobe_mutex);
p->ainsn.insn = get_insn_slot();
down(&kprobe_mutex);
if (!p->ainsn.insn) {
return -ENOMEM;
}
return 0;
}
/*
* Determine if the instruction uses the %rip-relative addressing mode.
* If it does, return the address of the 32-bit displacement word.
* If not, return null.
*/
static inline s32 *is_riprel(u8 *insn)
{
#define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf) \
(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) | \
(b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) | \
(b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) | \
(bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf)) \
<< (row % 64))
static const u64 onebyte_has_modrm[256 / 64] = {
/* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
/* ------------------------------- */
W(0x00, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 00 */
W(0x10, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 10 */
W(0x20, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 20 */
W(0x30, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0), /* 30 */
W(0x40, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 40 */
W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 50 */
W(0x60, 0,0,1,1,0,0,0,0,0,1,0,1,0,0,0,0)| /* 60 */
W(0x70, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 70 */
W(0x80, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 80 */
W(0x90, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 90 */
W(0xa0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* a0 */
W(0xb0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* b0 */
W(0xc0, 1,1,0,0,1,1,1,1,0,0,0,0,0,0,0,0)| /* c0 */
W(0xd0, 1,1,1,1,0,0,0,0,1,1,1,1,1,1,1,1)| /* d0 */
W(0xe0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* e0 */
W(0xf0, 0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1) /* f0 */
/* ------------------------------- */
/* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
};
static const u64 twobyte_has_modrm[256 / 64] = {
/* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
/* ------------------------------- */
W(0x00, 1,1,1,1,0,0,0,0,0,0,0,0,0,1,0,1)| /* 0f */
W(0x10, 1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0)| /* 1f */
W(0x20, 1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1)| /* 2f */
W(0x30, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 3f */
W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 4f */
W(0x50, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 5f */
W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 6f */
W(0x70, 1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1), /* 7f */
W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 8f */
W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 9f */
W(0xa0, 0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,1)| /* af */
W(0xb0, 1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1), /* bf */
W(0xc0, 1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0)| /* cf */
W(0xd0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* df */
W(0xe0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* ef */
W(0xf0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0) /* ff */
/* ------------------------------- */
/* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
};
#undef W
int need_modrm;
/* Skip legacy instruction prefixes. */
while (1) {
switch (*insn) {
case 0x66:
case 0x67:
case 0x2e:
case 0x3e:
case 0x26:
case 0x64:
case 0x65:
case 0x36:
case 0xf0:
case 0xf3:
case 0xf2:
++insn;
continue;
}
break;
}
/* Skip REX instruction prefix. */
if ((*insn & 0xf0) == 0x40)
++insn;
if (*insn == 0x0f) { /* Two-byte opcode. */
++insn;
need_modrm = test_bit(*insn, twobyte_has_modrm);
} else { /* One-byte opcode. */
need_modrm = test_bit(*insn, onebyte_has_modrm);
}
if (need_modrm) {
u8 modrm = *++insn;
if ((modrm & 0xc7) == 0x05) { /* %rip+disp32 addressing mode */
/* Displacement follows ModRM byte. */
return (s32 *) ++insn;
}
}
/* No %rip-relative addressing mode here. */
return NULL;
}
void arch_copy_kprobe(struct kprobe *p)
{
s32 *ripdisp;
memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE);
ripdisp = is_riprel(p->ainsn.insn);
if (ripdisp) {
/*
* The copied instruction uses the %rip-relative
* addressing mode. Adjust the displacement for the
* difference between the original location of this
* instruction and the location of the copy that will
* actually be run. The tricky bit here is making sure
* that the sign extension happens correctly in this
* calculation, since we need a signed 32-bit result to
* be sign-extended to 64 bits when it's added to the
* %rip value and yield the same 64-bit result that the
* sign-extension of the original signed 32-bit
* displacement would have given.
*/
s64 disp = (u8 *) p->addr + *ripdisp - (u8 *) p->ainsn.insn;
BUG_ON((s64) (s32) disp != disp); /* Sanity check. */
*ripdisp = disp;
}
p->opcode = *p->addr;
}
void 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 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 arch_remove_kprobe(struct kprobe *p)
{
up(&kprobe_mutex);
free_insn_slot(p->ainsn.insn);
down(&kprobe_mutex);
}
static inline void save_previous_kprobe(void)
{
kprobe_prev = current_kprobe;
kprobe_status_prev = kprobe_status;
kprobe_old_rflags_prev = kprobe_old_rflags;
kprobe_saved_rflags_prev = kprobe_saved_rflags;
}
static inline void restore_previous_kprobe(void)
{
current_kprobe = kprobe_prev;
kprobe_status = kprobe_status_prev;
kprobe_old_rflags = kprobe_old_rflags_prev;
kprobe_saved_rflags = kprobe_saved_rflags_prev;
}
static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs)
{
current_kprobe = p;
kprobe_saved_rflags = kprobe_old_rflags
= (regs->eflags & (TF_MASK | IF_MASK));
if (is_IF_modifier(p->ainsn.insn))
kprobe_saved_rflags &= ~IF_MASK;
}
static 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->rip = (unsigned long)p->addr;
else
regs->rip = (unsigned long)p->ainsn.insn;
}
struct task_struct *arch_get_kprobe_task(void *ptr)
{
return ((struct thread_info *) (((unsigned long) ptr) &
(~(THREAD_SIZE -1))))->task;
}
void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)
{
unsigned long *sara = (unsigned long *)regs->rsp;
struct kretprobe_instance *ri;
static void *orig_ret_addr;
/*
* Save the return address when the return probe hits
* the first time, and use it to populate the (krprobe
* instance)->ret_addr for subsequent return probes at
* the same addrress since stack address would have
* the kretprobe_trampoline by then.
*/
if (((void*) *sara) != kretprobe_trampoline)
orig_ret_addr = (void*) *sara;
if ((ri = get_free_rp_inst(rp)) != NULL) {
ri->rp = rp;
ri->stack_addr = sara;
ri->ret_addr = orig_ret_addr;
add_rp_inst(ri);
/* Replace the return addr with trampoline addr */
*sara = (unsigned long) &kretprobe_trampoline;
} else {
rp->nmissed++;
}
}
void arch_kprobe_flush_task(struct task_struct *tk)
{
struct kretprobe_instance *ri;
while ((ri = get_rp_inst_tsk(tk)) != NULL) {
*((unsigned long *)(ri->stack_addr)) =
(unsigned long) ri->ret_addr;
recycle_rp_inst(ri);
}
}
/*
* Interrupts are disabled on entry as trap3 is an interrupt gate and they
* remain disabled thorough out this function.
*/
int kprobe_handler(struct pt_regs *regs)
{
struct kprobe *p;
int ret = 0;
kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
/* We're in an interrupt, but this is clear and BUG()-safe. */
preempt_disable();
/* 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_rflags;
unlock_kprobes();
goto no_kprobe;
} else if (kprobe_status == KPROBE_HIT_SSDONE) {
/* TODO: Provide re-entrancy from
* post_kprobes_handler() and avoid exception
* stack corruption while single-stepping on
* the instruction of the new probe.
*/
arch_disarm_kprobe(p);
regs->rip = (unsigned long)p->addr;
ret = 1;
} else {
/* We have reentered the kprobe_handler(), since
* another probe was hit while within the
* handler. We here save the original kprobe
* variables and just single step on instruction
* of the new probe without calling any user
* handlers.
*/
save_previous_kprobe();
set_current_kprobe(p, regs);
p->nmissed++;
prepare_singlestep(p, regs);
kprobe_status = KPROBE_REENTER;
return 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 (*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;
set_current_kprobe(p, regs);
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;
}
/*
* 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 kretprobe_trampoline_holder(void)
{
asm volatile ( ".global kretprobe_trampoline\n"
"kretprobe_trampoline: \n"
"nop\n");
}
/*
* Called when we hit the probe point at kretprobe_trampoline
*/
int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
{
struct task_struct *tsk;
struct kretprobe_instance *ri;
struct hlist_head *head;
struct hlist_node *node;
unsigned long *sara = (unsigned long *)regs->rsp - 1;
tsk = arch_get_kprobe_task(sara);
head = kretprobe_inst_table_head(tsk);
hlist_for_each_entry(ri, node, head, hlist) {
if (ri->stack_addr == sara && ri->rp) {
if (ri->rp->handler)
ri->rp->handler(ri, regs);
}
}
return 0;
}
void trampoline_post_handler(struct kprobe *p, struct pt_regs *regs,
unsigned long flags)
{
struct kretprobe_instance *ri;
/* RA already popped */
unsigned long *sara = ((unsigned long *)regs->rsp) - 1;
while ((ri = get_rp_inst(sara))) {
regs->rip = (unsigned long)ri->ret_addr;
recycle_rp_inst(ri);
}
regs->eflags &= ~TF_MASK;
}
/*
* 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 rip 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 *)regs->rsp;
unsigned long next_rip = 0;
unsigned long copy_rip = (unsigned long)p->ainsn.insn;
unsigned long orig_rip = (unsigned long)p->addr;
kprobe_opcode_t *insn = p->ainsn.insn;
/*skip the REX prefix*/
if (*insn >= 0x40 && *insn <= 0x4f)
insn++;
switch (*insn) {
case 0x9c: /* pushfl */
*tos &= ~(TF_MASK | IF_MASK);
*tos |= kprobe_old_rflags;
break;
case 0xc3: /* ret/lret */
case 0xcb:
case 0xc2:
case 0xca:
regs->eflags &= ~TF_MASK;
/* rip is already adjusted, no more changes required*/
return;
case 0xe8: /* call relative - Fix return addr */
*tos = orig_rip + (*tos - copy_rip);
break;
case 0xff:
if ((*insn & 0x30) == 0x10) {
/* call absolute, indirect */
/* Fix return addr; rip is correct. */
next_rip = regs->rip;
*tos = orig_rip + (*tos - copy_rip);
} else if (((*insn & 0x31) == 0x20) || /* jmp near, absolute indirect */
((*insn & 0x31) == 0x21)) { /* jmp far, absolute indirect */
/* rip is correct. */
next_rip = regs->rip;
}
break;
case 0xea: /* jmp absolute -- rip is correct */
next_rip = regs->rip;
break;
default:
break;
}
regs->eflags &= ~TF_MASK;
if (next_rip) {
regs->rip = next_rip;
} else {
regs->rip = orig_rip + (regs->rip - copy_rip);
}
}
/*
* Interrupts are disabled on entry as trap1 is an interrupt gate and they
* remain disabled thoroughout this function. And we hold kprobe lock.
*/
int post_kprobe_handler(struct pt_regs *regs)
{
if (!kprobe_running())
return 0;
if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
kprobe_status = KPROBE_HIT_SSDONE;
current_kprobe->post_handler(current_kprobe, regs, 0);
}
if (current_kprobe->post_handler != trampoline_post_handler)
resume_execution(current_kprobe, regs);
regs->eflags |= kprobe_saved_rflags;
/* Restore the original saved kprobes variables and continue. */
if (kprobe_status == KPROBE_REENTER) {
restore_previous_kprobe();
goto out;
} else {
unlock_kprobes();
}
out:
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. */
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_rflags;
unlock_kprobes();
preempt_enable_no_resched();
}
return 0;
}
/*
* Wrapper routine 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_rsp = (long *) regs->rsp;
addr = (unsigned long)jprobe_saved_rsp;
/*
* 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->rip = (unsigned long)(jp->entry);
return 1;
}
void jprobe_return(void)
{
preempt_enable_no_resched();
asm volatile (" xchg %%rbx,%%rsp \n"
" int3 \n"
" .globl jprobe_return_end \n"
" jprobe_return_end: \n"
" nop \n"::"b"
(jprobe_saved_rsp):"memory");
}
int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
u8 *addr = (u8 *) (regs->rip - 1);
unsigned long stack_addr = (unsigned long)jprobe_saved_rsp;
struct jprobe *jp = container_of(p, struct jprobe, kp);
if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
if ((long *)regs->rsp != jprobe_saved_rsp) {
struct pt_regs *saved_regs =
container_of(jprobe_saved_rsp, struct pt_regs, rsp);
printk("current rsp %p does not match saved rsp %p\n",
(long *)regs->rsp, jprobe_saved_rsp);
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;
}
/*
* kprobe->ainsn.insn points to the copy of the instruction to be single-stepped.
* By default on x86_64, pages we get from kmalloc or vmalloc are not
* executable. Single-stepping an instruction on such a page yields an
* oops. So instead of storing the instruction copies in their respective
* kprobe objects, we allocate a page, map it executable, and store all the
* instruction copies there. (We can allocate additional pages if somebody
* inserts a huge number of probes.) Each page can hold up to INSNS_PER_PAGE
* instruction slots, each of which is MAX_INSN_SIZE*sizeof(kprobe_opcode_t)
* bytes.
*/
#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE*sizeof(kprobe_opcode_t)))
struct kprobe_insn_page {
struct hlist_node hlist;
kprobe_opcode_t *insns; /* page of instruction slots */
char slot_used[INSNS_PER_PAGE];
int nused;
};
static struct hlist_head kprobe_insn_pages;
/**
* get_insn_slot() - Find a slot on an executable page for an instruction.
* We allocate an executable page if there's no room on existing ones.
*/
static kprobe_opcode_t *get_insn_slot(void)
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
hlist_for_each(pos, &kprobe_insn_pages) {
kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
if (kip->nused < INSNS_PER_PAGE) {
int i;
for (i = 0; i < INSNS_PER_PAGE; i++) {
if (!kip->slot_used[i]) {
kip->slot_used[i] = 1;
kip->nused++;
return kip->insns + (i*MAX_INSN_SIZE);
}
}
/* Surprise! No unused slots. Fix kip->nused. */
kip->nused = INSNS_PER_PAGE;
}
}
/* All out of space. Need to allocate a new page. Use slot 0.*/
kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
if (!kip) {
return NULL;
}
/*
* For the %rip-relative displacement fixups to be doable, we
* need our instruction copy to be within +/- 2GB of any data it
* might access via %rip. That is, within 2GB of where the
* kernel image and loaded module images reside. So we allocate
* a page in the module loading area.
*/
kip->insns = module_alloc(PAGE_SIZE);
if (!kip->insns) {
kfree(kip);
return NULL;
}
INIT_HLIST_NODE(&kip->hlist);
hlist_add_head(&kip->hlist, &kprobe_insn_pages);
memset(kip->slot_used, 0, INSNS_PER_PAGE);
kip->slot_used[0] = 1;
kip->nused = 1;
return kip->insns;
}
/**
* free_insn_slot() - Free instruction slot obtained from get_insn_slot().
*/
static void free_insn_slot(kprobe_opcode_t *slot)
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
hlist_for_each(pos, &kprobe_insn_pages) {
kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
if (kip->insns <= slot
&& slot < kip->insns+(INSNS_PER_PAGE*MAX_INSN_SIZE)) {
int i = (slot - kip->insns) / MAX_INSN_SIZE;
kip->slot_used[i] = 0;
kip->nused--;
if (kip->nused == 0) {
/*
* Page is no longer in use. Free it unless
* it's the last one. We keep the last one
* so as not to have to set it up again the
* next time somebody inserts a probe.
*/
hlist_del(&kip->hlist);
if (hlist_empty(&kprobe_insn_pages)) {
INIT_HLIST_NODE(&kip->hlist);
hlist_add_head(&kip->hlist,
&kprobe_insn_pages);
} else {
module_free(NULL, kip->insns);
kfree(kip);
}
}
return;
}
}
}
