[RFC PATCH 2/3] arch/powerpc : optprobes for powerpc core

[Anju T]

Instruction slot for detour buffer is allocated from
the reserved area. For the time being 64KB is reserved
in memory for this purpose. ppc_get_optinsn_slot() and
ppc_free_optinsn_slot() are geared towards the allocation and freeing
of memory from this area.

Signed-off-by: Anju T <anju@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/kernel/optprobes.c | 463 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 463 insertions(+)
 create mode 100644 arch/powerpc/kernel/optprobes.c

diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
new file mode 100644
index 0000000..50a60c1
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,463 @@
+/*
+ * Code for Kernel probes Jump optimization.
+ *
+ * Copyright 2016, Anju T, IBM Corp.
+ *
+ * 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.
+ */
+
+#include <linux/kprobes.h>
+#include <linux/jump_label.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <asm/kprobes.h>
+#include <asm/ptrace.h>
+#include <asm/cacheflush.h>
+#include <asm/code-patching.h>
+#include <asm/sstep.h>
+
+/* Reserve an area to allocate slots for detour buffer */
+extern void  optprobe_trampoline_holder(void)
+{
+	asm volatile(".global optinsn_slot\n"
+			"optinsn_slot:\n"
+			".space 65536");
+}
+
+#define SLOT_SIZE 65536
+#define TMPL_CALL_HDLR_IDX	\
+	(optprobe_template_call_handler - optprobe_template_entry)
+#define TMPL_EMULATE_IDX	\
+	(optprobe_template_call_emulate - optprobe_template_entry)
+#define TMPL_RET_BRANCH_IDX	\
+	(optprobe_template_ret_branch - optprobe_template_entry)
+#define TMPL_RET_IDX	\
+	(optprobe_template_ret - optprobe_template_entry)
+#define TMPL_OP1_IDX	\
+	(optprobe_template_op_address1 - optprobe_template_entry)
+#define TMPL_OP2_IDX	\
+	(optprobe_template_op_address2 - optprobe_template_entry)
+#define TMPL_INSN_IDX	\
+	(optprobe_template_insn - optprobe_template_entry)
+#define TMPL_END_IDX	\
+	(optprobe_template_end - optprobe_template_entry)
+
+struct kprobe_ppc_insn_page {
+	struct list_head list;
+	kprobe_opcode_t *insns;	/* Page of instruction slots */
+	struct kprobe_insn_cache *cache;
+	int nused;
+	int ngarbage;
+	char slot_used[];
+};
+
+#define PPC_KPROBE_INSN_PAGE_SIZE(slots)	\
+	(offsetof(struct kprobe_ppc_insn_page, slot_used) +	\
+	(sizeof(char) * (slots)))
+
+enum ppc_kprobe_slot_state {
+	SLOT_CLEAN = 0,
+	SLOT_DIRTY = 1,
+	SLOT_USED = 2,
+};
+
+static struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
+	.mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
+	.pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
+	/* .insn_size is initialized later */
+	.nr_garbage = 0,
+};
+
+static int ppc_slots_per_page(struct kprobe_insn_cache *c)
+{
+	/*
+	 * Here the #slots per page differs from x86 as we have
+	 * only 64KB reserved.
+	 */
+	return SLOT_SIZE / (c->insn_size * sizeof(kprobe_opcode_t));
+}
+
+/* Return 1 if all garbages are collected, otherwise 0. */
+static int collect_one_slot(struct kprobe_ppc_insn_page *kip, int idx)
+{
+	kip->slot_used[idx] = SLOT_CLEAN;
+	kip->nused--;
+	return 0;
+}
+
+static int collect_garbage_slots(struct kprobe_insn_cache *c)
+{
+	struct kprobe_ppc_insn_page *kip, *next;
+
+	/* Ensure no-one is interrupted on the garbages */
+	synchronize_sched();
+
+	list_for_each_entry_safe(kip, next, &c->pages, list) {
+		int i;
+
+		if (kip->ngarbage == 0)
+			continue;
+		kip->ngarbage = 0;	/* we will collect all garbages */
+		for (i = 0; i < ppc_slots_per_page(c); i++) {
+			if (kip->slot_used[i] == SLOT_DIRTY &&
+			    collect_one_slot(kip, i))
+				break;
+		}
+	}
+	c->nr_garbage = 0;
+	return 0;
+}
+
+kprobe_opcode_t  *__ppc_get_optinsn_slot(struct kprobe_insn_cache *c)
+{
+	struct kprobe_ppc_insn_page *kip;
+	kprobe_opcode_t *slot = NULL;
+
+	mutex_lock(&c->mutex);
+	list_for_each_entry(kip, &c->pages, list) {
+		if (kip->nused < ppc_slots_per_page(c)) {
+			int i;
+
+			for (i = 0; i < ppc_slots_per_page(c); i++) {
+				if (kip->slot_used[i] == SLOT_CLEAN) {
+					kip->slot_used[i] = SLOT_USED;
+					kip->nused++;
+					slot = kip->insns + (i * c->insn_size);
+					goto out;
+				}
+			}
+			/* kip->nused reached max value. */
+			kip->nused = ppc_slots_per_page(c);
+			pr_info("No more slots to allocate\n");
+			WARN_ON(1);
+			goto out;
+		}
+	}
+	kip = kmalloc(PPC_KPROBE_INSN_PAGE_SIZE(ppc_slots_per_page(c)),
+		      GFP_KERNEL);
+	if (!kip)
+		goto out;
+	/*
+	 * Allocate from the reserved area so as to
+	 * ensure the range will be within +/-32MB
+	 */
+	kip->insns = &optinsn_slot;
+	if (!kip->insns) {
+		kfree(kip);
+		goto out;
+	}
+	INIT_LIST_HEAD(&kip->list);
+	memset(kip->slot_used, SLOT_CLEAN, ppc_slots_per_page(c));
+	kip->slot_used[0] = SLOT_USED;
+	kip->nused = 1;
+	kip->ngarbage = 0;
+	kip->cache = c;
+	list_add(&kip->list, &c->pages);
+	slot = kip->insns;
+out:
+	mutex_unlock(&c->mutex);
+	return slot;
+}
+
+kprobe_opcode_t *ppc_get_optinsn_slot(struct optimized_kprobe *op)
+{
+	/*
+	 * The insn slot is allocated from the reserved
+	 * area(ie &optinsn_slot).We are not optimizing probes
+	 * at module_addr now.
+	 */
+	kprobe_opcode_t *slot = NULL;
+
+	if (is_kernel_addr(op->kp.addr))
+		slot = __ppc_get_optinsn_slot(&kprobe_ppc_optinsn_slots);
+	else
+		pr_info("Kprobe can not be optimized\n");
+	return slot;
+}
+NOKPROBE_SYMBOL(ppc_get_optinsn_slot);
+
+void __ppc_free_optinsn_slot(struct kprobe_insn_cache *c,
+			     kprobe_opcode_t *slot, int dirty)
+{
+	struct kprobe_ppc_insn_page *kip;
+
+	mutex_lock(&c->mutex);
+
+	list_for_each_entry(kip, &c->pages, list) {
+		long idx = ((long)slot - (long)kip->insns) /
+				(c->insn_size * sizeof(kprobe_opcode_t));
+		if (idx >= 0 && idx < ppc_slots_per_page(c)) {
+			WARN_ON(kip->slot_used[idx] != SLOT_USED);
+			if (dirty) {
+				kip->slot_used[idx] = SLOT_DIRTY;
+				kip->ngarbage++;
+				if (++c->nr_garbage > ppc_slots_per_page(c))
+					collect_garbage_slots(c);
+			} else
+				collect_one_slot(kip, idx);
+			goto out;
+		}
+	}
+	/* Could not free this slot. */
+	WARN_ON(1);
+out:
+	mutex_unlock(&c->mutex);
+}
+
+static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
+{
+	if (!op->optinsn.insn)
+		return;
+	if (is_kernel_addr((unsigned long)op->kp.addr))
+		__ppc_free_optinsn_slot(&kprobe_ppc_optinsn_slots,
+					op->optinsn.insn, 0);
+}
+NOKPROBE_SYMBOL(ppc_free_optinsn_slot);
+
+static void
+__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
+{
+	if (op->optinsn.insn) {
+		ppc_free_optinsn_slot(op);
+		op->optinsn.insn = NULL;
+	}
+}
+
+static int can_optimize(struct kprobe *p)
+{
+	/*
+	 * Not optimizing the kprobe placed by
+	 * kretprobe during boot time
+	 */
+	struct pt_regs *regs;
+	unsigned int instr;
+	int r;
+
+	if ((kprobe_opcode_t)p->addr == (kprobe_opcode_t)&kretprobe_trampoline)
+		return 0;
+
+	regs = current_pt_regs();
+	instr = *(p->ainsn.insn);
+
+	/* Ensure the instruction can be emulated*/
+	r = emulate_step(regs, instr);
+	if (r != 1)
+		return 0;
+
+	return 1;
+}
+
+static void
+create_return_branch(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+	/*
+	 * Create a branch back to the return address
+	 * after the probed instruction is emulated
+	 */
+
+	kprobe_opcode_t branch, *buff;
+	unsigned long ret;
+
+	ret = regs->nip;
+	buff = op->optinsn.insn;
+
+	branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
+			       (unsigned long)ret, 0);
+	buff[TMPL_RET_IDX] = branch;
+}
+NOKPROBE_SYMBOL(create_return_branch);
+
+static void
+optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	if (kprobe_running())
+		kprobes_inc_nmissed_count(&op->kp);
+	else {
+		__this_cpu_write(current_kprobe, &op->kp);
+		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+		opt_pre_handler(&op->kp, regs);
+		__this_cpu_write(current_kprobe, NULL);
+	}
+	local_irq_restore(flags);
+}
+
+void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
+{
+	 __arch_remove_optimized_kprobe(op, 1);
+}
+
+void  create_insn(unsigned int insn, kprobe_opcode_t *addr)
+{
+	unsigned int instr, instr2;
+
+	instr = 0x3c000000 | 0x800000 | ((insn >> 16) & 0xffff);
+	*addr++ = instr;
+	instr2 = 0x60000000 | 0x40000 | 0x800000;
+	instr2 = instr2 | (insn & 0xffff);
+	*addr = instr2;
+}
+
+void create_load_address_insn(struct optimized_kprobe *op,
+			      kprobe_opcode_t *addr, kprobe_opcode_t *addr2)
+{
+	unsigned int instr1, instr2, instr3, instr4, instr5;
+	unsigned long val;
+
+	val = op;
+
+	instr1 = 0x3c000000 | 0x600000 | ((val >> 48) & 0xffff);
+	*addr++ = instr1;
+	*addr2++ = instr1;
+	instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
+	*addr++ = instr2;
+	*addr2++ = instr2;
+	instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
+	instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
+	*addr++ = instr3;
+	*addr2++ = instr3;
+	instr4 = 0x64000000 |  0x30000 | 0x600000 | ((val >> 16) & 0xffff);
+	*addr++ = instr4;
+	*addr2++ = instr4;
+	instr5 =  0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
+	*addr = instr5;
+	*addr2 = instr5;
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
+{
+	kprobe_opcode_t *buff, branch, branch2, branch3;
+	long rel_chk, ret_chk;
+
+	kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
+	op->optinsn.insn = NULL;
+
+	if (!can_optimize(p))
+		return -EILSEQ;
+
+	/* Allocate instruction slot for detour buffer*/
+	buff = ppc_get_optinsn_slot(op);
+
+	/*
+	 * OPTPROBE use a 'b' instruction to branch to optinsn.insn.
+	 *
+	 * The target address has to be relatively nearby, to permit use
+	 * of branch instruction in powerpc because the address is specified
+	 * in an immediate field in the instruction opcode itself, ie 24 bits
+	 * in the opcode specify the address. Therefore the address gap should
+	 * be 32MB on either side of the current instruction.
+	 */
+	rel_chk = (long)buff -
+			(unsigned long)p->addr;
+	if (rel_chk < -0x2000000 || rel_chk > 0x1fffffc || rel_chk & 0x3) {
+		ppc_free_optinsn_slot(op);
+		return -ERANGE;
+	}
+	/*
+	 * For the time being assume that the return address is NIP+4.
+	 * TODO : check the return address is also within 32MB range for
+	 * cases where NIP is not NIP+4.ie the NIP is decided after emulation.
+	 */
+	ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)(p->addr) + 4;
+
+	if (ret_chk < -0x2000000 || ret_chk > 0x1fffffc || ret_chk & 0x3) {
+		ppc_free_optinsn_slot(op);
+		return -ERANGE;
+	}
+
+	/* Do Copy arch specific instance from template*/
+	memcpy(buff, optprobe_template_entry,
+	       TMPL_END_IDX * sizeof(kprobe_opcode_t));
+	create_load_address_insn(op, buff + TMPL_OP1_IDX, buff + TMPL_OP2_IDX);
+
+	/* Create a branch to the optimized_callback function */
+	branch = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
+			       (unsigned long)optimized_callback + 8,
+				BRANCH_SET_LINK);
+
+	/* Place the branch instr into the trampoline */
+	buff[TMPL_CALL_HDLR_IDX] = branch;
+	create_insn(*(p->ainsn.insn), buff + TMPL_INSN_IDX);
+
+	/*Create a branch instruction into the emulate_step*/
+	branch3 = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
+				(unsigned long)emulate_step + 8,
+				BRANCH_SET_LINK);
+	buff[TMPL_EMULATE_IDX] = branch3;
+
+	/* Create a branch for jumping back*/
+	branch2 = create_branch((unsigned int *)buff + TMPL_RET_BRANCH_IDX,
+				(unsigned long)create_return_branch + 8,
+				BRANCH_SET_LINK);
+	buff[TMPL_RET_BRANCH_IDX] = branch2;
+
+	op->optinsn.insn = buff;
+	return 0;
+}
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+	return optinsn->insn;
+}
+
+/*
+ * Here,kprobe opt always replace one instruction (4 bytes
+ * aligned and 4 bytes long). It is impossible to encounter another
+ * kprobe in the address range. So always return 0.
+ */
+int arch_check_optimized_kprobe(struct optimized_kprobe *op)
+{
+	return 0;
+}
+
+void arch_optimize_kprobes(struct list_head *oplist)
+{
+	struct optimized_kprobe *op;
+	struct optimized_kprobe *tmp;
+
+	unsigned int branch;
+
+	list_for_each_entry_safe(op, tmp, oplist, list) {
+	/*
+	* Backup instructions which will be replaced
+	* by jump address
+	*/
+	memcpy(op->optinsn.copied_insn, op->kp.addr,
+	       RELATIVEJUMP_SIZE);
+	branch = create_branch((unsigned int *)op->kp.addr,
+			       (unsigned long)op->optinsn.insn, 0);
+	*op->kp.addr = branch;
+	list_del_init(&op->list);
+	}
+}
+
+void arch_unoptimize_kprobe(struct optimized_kprobe *op)
+{
+	arch_arm_kprobe(&op->kp);
+}
+
+void arch_unoptimize_kprobes(struct list_head *oplist,
+			     struct list_head *done_list)
+{
+	struct optimized_kprobe *op;
+	struct optimized_kprobe *tmp;
+
+	list_for_each_entry_safe(op, tmp, oplist, list) {
+		arch_unoptimize_kprobe(op);
+		list_move(&op->list, done_list);
+	}
+}
+
+int arch_within_optimized_kprobe(struct optimized_kprobe *op,
+				 unsigned long addr)
+{
+	return 0;
+}
-- 
2.1.0