[RFC PATCH v3 2/3] arch/powerpc : optprobes for powerpc core

[Anju T]

Instructions which can be emulated are suppliants for
optimization. Before optimization ensure that the address range
between the detour buffer allocated and the instruction being probed
is within +/- 32MB.

Signed-off-by: Anju T <anju@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/kernel/optprobes.c | 351 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 351 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..c4253b6
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,351 @@
+/*
+ * 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>
+
+DEFINE_INSN_CACHE_OPS(ppc_optinsn)
+
+#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_KP_IDX	\
+	(optprobe_template_kp_addr - 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)
+
+static unsigned long val_nip;
+
+static void *__ppc_alloc_insn_page(void)
+{
+	return &optinsn_slot;
+}
+
+static void *__ppc_free_insn_page(void *page __maybe_unused)
+{
+	return;
+}
+
+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 initialized later */
+	.alloc = __ppc_alloc_insn_page,
+	.free = __ppc_free_insn_page,
+	.nr_garbage = 0,
+};
+
+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 = get_ppc_optinsn_slot();
+	return slot;
+}
+
+static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
+{
+	if (!op->optinsn.insn)
+		return;
+	if (is_kernel_addr((unsigned long)op->kp.addr))
+		free_ppc_optinsn_slot(op->optinsn.insn, 0);
+}
+
+static void
+__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
+{
+	ppc_free_optinsn_slot(op);
+	op->optinsn.insn = NULL;
+}
+
+static int can_optimize(struct kprobe *p)
+{
+	struct pt_regs *regs;
+	unsigned int instr;
+	int r;
+
+	/*
+	 * Not optimizing the kprobe placed by
+	 * kretprobe during boot time
+	 */
+	if ((kprobe_opcode_t)p->addr == (kprobe_opcode_t)&kretprobe_trampoline)
+		return 0;
+
+	regs = kmalloc(sizeof(*regs), GFP_KERNEL);
+	if (!regs)
+		return -ENOMEM;
+	memset(regs, 0, sizeof(struct pt_regs));
+	memcpy(regs, current_pt_regs(), sizeof(struct pt_regs));
+	regs->nip = p->addr;
+	instr = *(p->ainsn.insn);
+
+	/* Ensure the instruction can be emulated*/
+	r = emulate_step(regs, instr);
+	val_nip = regs->nip;
+	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;
+	/*
+	 * TODO: For conditional branch instructions, the return
+	 * address may differ in SMP systems.This has to be addressed.
+	 */
+
+	branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
+			       (unsigned long)ret, 0);
+	buff[TMPL_RET_IDX] = branch;
+	isync();
+}
+
+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);
+}
+NOKPROBE_SYMBOL(optimized_callback);
+
+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)
+{
+	u32 instr, instr2;
+
+	/*
+	 * emulate_step() requires insn to be emulated as
+	 * second parameter. Hence r4 should be loaded
+	 * with 'insn'.
+	 * synthesize addis r4,0,(insn)@h
+	 */
+	instr = 0x3c000000 | 0x800000 | ((insn >> 16) & 0xffff);
+	*addr++ = instr;
+
+	/* ori r4,r4,(insn)@l */
+	instr2 = 0x60000000 | 0x40000 | 0x800000;
+	instr2 = instr2 | (insn & 0xffff);
+	*addr = instr2;
+}
+
+void create_load_address_insn(unsigned long val, kprobe_opcode_t *addr)
+{
+	u32 instr1, instr2, instr3, instr4, instr5;
+	/*
+	 * Optimized_kprobe structure is required as a parameter
+	 * for invoking optimized_callback() and create_return_branch()
+	 * from detour buffer. Hence need to have a 64bit immediate
+	 * load into r3.
+	 *
+	 * lis r3,(op)@highest
+	 */
+	instr1 = 0x3c000000 | 0x600000 | ((val >> 48) & 0xffff);
+	*addr++ = instr1;
+
+	/* ori r3,r3,(op)@higher */
+	instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
+	*addr++ = instr2;
+
+	/* rldicr r3,r3,32,31 */
+	instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
+	instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
+	*addr++ = instr3;
+
+	/* oris r3,r3,(op)@h */
+	instr4 = 0x64000000 |  0x30000 | 0x600000 | ((val >> 16) & 0xffff);
+	*addr++ = instr4;
+
+	/* ori r3,r3,(op)@l */
+	instr5 =  0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
+	*addr = 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);
+	if (!buff)
+		return -ENOMEM;
+
+	/*
+	 * 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;
+	}
+	/* Check the return address is also within 32MB range */
+	ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)val_nip;
+	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((unsigned long)p->addr, buff + TMPL_KP_IDX);
+	create_load_address_insn((unsigned long)op, buff + TMPL_OP1_IDX);
+	create_load_address_insn((unsigned long)op, 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;
+	smp_mb();
+	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