Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 631 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
new file mode 100644
index 000000000000..4f2a852299b6
--- /dev/null
+++ b/arch/x86_64/kernel/kprobes.c
@@ -0,0 +1,631 @@
+/*
+ *  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.
+ */
+
+#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/pgtable.h>
+#include <asm/kdebug.h>
+
+static DECLARE_MUTEX(kprobe_mutex);
+
+/* 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_rflags, kprobe_saved_rflags;
+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;
+	}
+}
+
+void arch_remove_kprobe(struct kprobe *p)
+{
+	up(&kprobe_mutex);
+	free_insn_slot(p->ainsn.insn);
+	down(&kprobe_mutex);
+}
+
+static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
+{
+	*p->addr = p->opcode;
+	regs->rip = (unsigned long)p->addr;
+}
+
+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;
+}
+
+/*
+ * 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;
+			}
+			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 (*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_rflags = kprobe_old_rflags
+	    = (regs->eflags & (TF_MASK | IF_MASK));
+	if (is_IF_modifier(p->ainsn.insn))
+		kprobe_saved_rflags &= ~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 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 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 (current_kprobe->post_handler)
+		current_kprobe->post_handler(current_kprobe, regs, 0);
+
+	resume_execution(current_kprobe, regs);
+	regs->eflags |= kprobe_saved_rflags;
+
+	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. */
+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;
+		}
+	}
+}