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

[Anju T Sudhakar]

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 Sudhakar <anju@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/sstep.h |   1 +
 arch/powerpc/kernel/optprobes.c  | 329 +++++++++++++++++++++++++++++++++++++++
 arch/powerpc/lib/sstep.c         |  21 +++
 3 files changed, 351 insertions(+)
 create mode 100644 arch/powerpc/kernel/optprobes.c

diff --git a/arch/powerpc/include/asm/sstep.h b/arch/powerpc/include/asm/sstep.h
index d3a42cc..cd5f6ab 100644
--- a/arch/powerpc/include/asm/sstep.h
+++ b/arch/powerpc/include/asm/sstep.h
@@ -25,6 +25,7 @@ struct pt_regs;
 
 /* Emulate instructions that cause a transfer of control. */
 extern int emulate_step(struct pt_regs *regs, unsigned int instr);
+extern int optprobe_conditional_branch_check(unsigned int instr);
 
 enum instruction_type {
 	COMPUTE,		/* arith/logical/CR op, etc. */
diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
new file mode 100644
index 0000000..7983d07
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,329 @@
+/*
+ * 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_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_INSN_IDX	\
+	(optprobe_template_insn - optprobe_template_entry)
+#define TMPL_END_IDX	\
+	(optprobe_template_end - optprobe_template_entry)
+
+static bool insn_page_in_use;
+
+static void *__ppc_alloc_insn_page(void)
+{
+	if (insn_page_in_use)
+		return NULL;
+	insn_page_in_use = true;
+	return &optinsn_slot;
+}
+
+static void __ppc_free_insn_page(void *page __maybe_unused)
+{
+	insn_page_in_use = false;
+}
+
+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.
+	 */
+	if (is_kernel_addr((unsigned long)op->kp.addr))
+		return get_ppc_optinsn_slot();
+	return NULL;
+}
+
+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 unsigned long can_optimize(struct kprobe *p)
+{
+	struct pt_regs *regs;
+	unsigned int instr;
+
+	/*
+	 * Not optimizing the kprobe placed by
+	 * kretprobe during boot time
+	 */
+	if (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 = (unsigned long)p->addr;
+	instr = *p->ainsn.insn;
+
+	/* Ensure the instruction can be emulated */
+	if (emulate_step(regs, instr) != 1)
+		return 0;
+	/* Conditional branches are not optimized */
+	if (optprobe_conditional_branch_check(instr) != 1)
+		return 0;
+	return regs->nip;
+}
+
+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)
+{
+	ppc_free_optinsn_slot(op);
+	op->optinsn.insn = NULL;
+}
+
+/*
+ * emulate_step() requires insn to be emulated as
+ * second parameter. Load register 'r4' with the
+ * instruction.
+ */
+void create_load_emulate_insn(unsigned int insn, kprobe_opcode_t *addr)
+{
+	u32 instr, instr2;
+
+	/* 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;
+}
+
+/*
+ * optimized_kprobe structure is required as a parameter
+ * for invoking optimized_callback() from detour buffer.
+ * Load this value into register 'r3'.
+ */
+void create_load_address_insn(unsigned long val, kprobe_opcode_t *addr)
+{
+	u32 instr1, instr2, instr3, instr4, instr5;
+	/*
+	 * 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;
+	unsigned long nip;
+
+	kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
+	op->optinsn.insn = NULL;
+	nip = can_optimize(p);
+
+	if (!nip)
+		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)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));
+
+	/* Load address into register */
+	create_load_address_insn((unsigned long)p->addr, buff + TMPL_KP_IDX);
+	create_load_address_insn((unsigned long)op, buff + TMPL_OP1_IDX);
+
+	/*
+	 * Create a branch to the optimized_callback function.
+	 * optimized_callback, points to the global entry point.
+	 * Add +8, to create a branch to the LEP of the 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;
+
+	/* Load instruction to be emulated into relevant register */
+	create_load_emulate_insn(*p->ainsn.insn, buff + TMPL_INSN_IDX);
+
+	/*
+	 * Create a branch instruction into the emulate_step.
+	 * Add +8, to create the branch to LEP of 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_IDX,
+				(unsigned long)nip, 0);
+	buff[TMPL_RET_IDX] = branch2;
+
+	op->optinsn.insn = buff;
+	smp_mb();
+	return 0;
+}
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+	return optinsn->insn != NULL;
+}
+
+/*
+ * 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;
+}
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 3362299..c4b8259 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -2018,3 +2018,24 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
 	regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
 	return 1;
 }
+
+/* Before optimizing, ensure that the probed instruction is not a
+ * conditional branch instruction
+ */
+int __kprobes optprobe_conditional_branch_check(unsigned int instr)
+{
+	unsigned int opcode;
+
+	opcode = instr >> 26;
+	if (opcode == 16)
+		return 0;
+	if (opcode == 19) {
+		switch ((instr >> 1) & 0x3ff) {
+		case 16:        /* bclr, bclrl */
+		case 528:       /* bcctr, bcctrl */
+		case 560:       /* bctar, bctarl */
+			return 0;
+		}
+	}
+	return 1;
+}
-- 
1.8.3.1