[PATCH V2 3/4] arch/powerpc: Implement Optprobes

[Anju T Sudhakar]

Detour buffer contains instructions to create an in memory pt_regs.
After the execution of the pre-handler, a call is made for instruction emulation.
The NIP is determined in advanced through dummy instruction emulation and a branch
instruction is created to the NIP at the end of the trampoline.

Instruction slot for detour buffer is allocated from the reserved area.
For the time being, 64KB is reserved in memory for this purpose.

Instructions which can be emulated using analyse_instr() 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>
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
 .../features/debug/optprobes/arch-support.txt      |   2 +-
 arch/powerpc/Kconfig                               |   1 +
 arch/powerpc/include/asm/kprobes.h                 |  23 +-
 arch/powerpc/include/asm/sstep.h                   |   1 +
 arch/powerpc/kernel/Makefile                       |   1 +
 arch/powerpc/kernel/optprobes.c                    | 333 +++++++++++++++++++++
 arch/powerpc/kernel/optprobes_head.S               | 135 +++++++++
 arch/powerpc/lib/sstep.c                           |  22 ++
 8 files changed, 516 insertions(+), 2 deletions(-)
 create mode 100644 arch/powerpc/kernel/optprobes.c
 create mode 100644 arch/powerpc/kernel/optprobes_head.S

diff --git a/Documentation/features/debug/optprobes/arch-support.txt b/Documentation/features/debug/optprobes/arch-support.txt
index b8999d8..45bc99d 100644
--- a/Documentation/features/debug/optprobes/arch-support.txt
+++ b/Documentation/features/debug/optprobes/arch-support.txt
@@ -27,7 +27,7 @@
     |       nios2: | TODO |
     |    openrisc: | TODO |
     |      parisc: | TODO |
-    |     powerpc: | TODO |
+    |     powerpc: |  ok  |
     |        s390: | TODO |
     |       score: | TODO |
     |          sh: | TODO |
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c7f120a..d563f0a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -98,6 +98,7 @@ config PPC
 	select HAVE_IOREMAP_PROT
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
 	select HAVE_KPROBES
+	select HAVE_OPTPROBES if PPC64
 	select HAVE_ARCH_KGDB
 	select HAVE_KRETPROBES
 	select HAVE_ARCH_TRACEHOOK
diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index 2c9759bd..739ddc5 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -38,7 +38,22 @@ struct pt_regs;
 struct kprobe;
 
 typedef ppc_opcode_t kprobe_opcode_t;
-#define MAX_INSN_SIZE 1
+
+extern kprobe_opcode_t optinsn_slot;
+
+/* Optinsn template address */
+extern kprobe_opcode_t optprobe_template_entry[];
+extern kprobe_opcode_t optprobe_template_op_address[];
+extern kprobe_opcode_t optprobe_template_call_handler[];
+extern kprobe_opcode_t optprobe_template_insn[];
+extern kprobe_opcode_t optprobe_template_call_emulate[];
+extern kprobe_opcode_t optprobe_template_ret[];
+extern kprobe_opcode_t optprobe_template_end[];
+
+#define MAX_INSN_SIZE		1
+#define MAX_OPTIMIZED_LENGTH	4
+#define MAX_OPTINSN_SIZE	(optprobe_template_end - optprobe_template_entry)
+#define RELATIVEJUMP_SIZE	4
 
 #ifdef PPC64_ELF_ABI_v2
 /* PPC64 ABIv2 needs local entry point */
@@ -124,6 +139,12 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+struct arch_optimized_insn {
+	kprobe_opcode_t copied_insn[1];
+	/* detour buffer */
+	kprobe_opcode_t *insn;
+};
+
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 					unsigned long val, void *data);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
diff --git a/arch/powerpc/include/asm/sstep.h b/arch/powerpc/include/asm/sstep.h
index d3a42cc..f7ad425 100644
--- a/arch/powerpc/include/asm/sstep.h
+++ b/arch/powerpc/include/asm/sstep.h
@@ -87,3 +87,4 @@ struct instruction_op {
 
 extern int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
 			 unsigned int instr);
+extern bool is_conditional_branch(unsigned int instr);
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 1925341..54f0f47 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -98,6 +98,7 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_BOOTX_TEXT)	+= btext.o
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
+obj-$(CONFIG_OPTPROBES)		+= optprobes.o optprobes_head.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o
 obj-$(CONFIG_PPC_UDBG_16550)	+= legacy_serial.o udbg_16550.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
new file mode 100644
index 0000000..ecba221
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,333 @@
+/*
+ * 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>
+#include <asm/ppc-opcode.h>
+
+#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_OP_IDX		\
+	(optprobe_template_op_address - optprobe_template_entry)
+#define TMPL_INSN_IDX		\
+	(optprobe_template_insn - optprobe_template_entry)
+#define TMPL_END_IDX		\
+	(optprobe_template_end - optprobe_template_entry)
+
+DEFINE_INSN_CACHE_OPS(ppc_optinsn);
+
+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,
+};
+
+/*
+ * Check if we can optimize this probe. Returns NIP post-emulation if this can
+ * be optimized and 0 otherwise.
+ */
+static unsigned long can_optimize(struct kprobe *p)
+{
+	struct pt_regs regs;
+	struct instruction_op op;
+	unsigned long nip = 0;
+
+	/*
+	 * kprobe placed for kretprobe during boot time
+	 * is not optimizing now.
+	 *
+	 * TODO: Optimize kprobe in kretprobe_trampoline
+	 */
+	if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
+		return 0;
+
+	/*
+	 * We only support optimizing kernel addresses, but not
+	 * module addresses.
+	 */
+	if (!is_kernel_addr((unsigned long)p->addr))
+		return 0;
+
+	regs.nip = (unsigned long)p->addr;
+	regs.trap = 0x0;
+	regs.msr = MSR_KERNEL;
+
+	/*
+	 * Ensure that the instruction is not a conditional branch,
+	 * and that can be emulated.
+	 */
+	if (!is_conditional_branch(*p->ainsn.insn) &&
+			analyse_instr(&op, &regs, *p->ainsn.insn))
+		nip = regs.nip;
+
+	return nip;
+}
+
+static void optimized_callback(struct optimized_kprobe *op,
+			       struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long flags;
+
+	/* This is possible if op is under delayed unoptimizing */
+	if (kprobe_disabled(&op->kp))
+		return;
+
+	local_irq_save(flags);
+
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(&op->kp);
+	} else {
+		__this_cpu_write(current_kprobe, &op->kp);
+		regs->nip = (unsigned long)op->kp.addr;
+		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)
+{
+	if (op->optinsn.insn) {
+		free_ppc_optinsn_slot(op->optinsn.insn, 1);
+		op->optinsn.insn = NULL;
+	}
+}
+
+/*
+ * emulate_step() requires insn to be emulated as
+ * second parameter. Load register 'r4' with the
+ * instruction.
+ */
+void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
+{
+	/* addis r4,0,(insn)@h */
+	*addr++ = PPC_INST_ADDIS | ___PPC_RT(4) |
+		  ((val >> 16) & 0xffff);
+
+	/* ori r4,r4,(insn)@l */
+	*addr = PPC_INST_ORI | ___PPC_RA(4) | ___PPC_RS(4) |
+		(val & 0xffff);
+}
+
+/*
+ * Generate instructions to load provided immediate 64-bit value
+ * to register 'r3' and patch these instructions at 'addr'.
+ */
+void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
+{
+	/* lis r3,(op)@highest */
+	*addr++ = PPC_INST_ADDIS | ___PPC_RT(3) |
+		  ((val >> 48) & 0xffff);
+
+	/* ori r3,r3,(op)@higher */
+	*addr++ = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
+		  ((val >> 32) & 0xffff);
+
+	/* rldicr r3,r3,32,31 */
+	*addr++ = PPC_INST_RLDICR | ___PPC_RA(3) | ___PPC_RS(3) |
+		  __PPC_SH64(32) | __PPC_ME64(31);
+
+	/* oris r3,r3,(op)@h */
+	*addr++ = PPC_INST_ORIS | ___PPC_RA(3) | ___PPC_RS(3) |
+		  ((val >> 16) & 0xffff);
+
+	/* ori r3,r3,(op)@l */
+	*addr = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
+		(val & 0xffff);
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
+{
+	kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
+	kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
+	long b_offset;
+	unsigned long nip;
+
+	kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
+
+	nip = can_optimize(p);
+	if (!nip)
+		return -EILSEQ;
+
+	/* Allocate instruction slot for detour buffer */
+	buff = get_ppc_optinsn_slot();
+	if (!buff)
+		return -ENOMEM;
+
+	/*
+	 * OPTPROBE uses '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 should
+	 * be within 32MB on either side of the current instruction.
+	 */
+	b_offset = (unsigned long)buff - (unsigned long)p->addr;
+	if (!is_offset_in_branch_range(b_offset)) {
+		free_ppc_optinsn_slot(buff, 0);
+		return -ERANGE;
+	}
+
+	/* Check if the return address is also within 32MB range */
+	b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
+			(unsigned long)nip;
+	if (!is_offset_in_branch_range(b_offset)) {
+		free_ppc_optinsn_slot(buff, 0);
+		return -ERANGE;
+	}
+
+	/* Setup template */
+	memcpy(buff, optprobe_template_entry,
+			TMPL_END_IDX * sizeof(kprobe_opcode_t));
+
+	/*
+	 * Fixup the template with instructions to:
+	 * 1. load the address of the actual probepoint
+	 */
+	patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
+
+	/*
+	 * 2. branch to optimized_callback() and emulate_step()
+	 */
+	kprobe_lookup_name("optimized_callback", op_callback_addr);
+	kprobe_lookup_name("emulate_step", emulate_step_addr);
+	if (!op_callback_addr || !emulate_step_addr) {
+		free_ppc_optinsn_slot(buff, 0);
+		WARN(1, "kprobe_lookup_name() failed\n");
+		return -ENOENT;
+	}
+
+	branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
+				(unsigned long)op_callback_addr,
+				BRANCH_SET_LINK);
+
+	branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
+				(unsigned long)emulate_step_addr,
+				BRANCH_SET_LINK);
+
+	if (!branch_op_callback || !branch_emulate_step) {
+		free_ppc_optinsn_slot(buff, 0);
+		return -ERANGE;
+	}
+
+	buff[TMPL_CALL_HDLR_IDX] = branch_op_callback;
+	buff[TMPL_EMULATE_IDX] = branch_emulate_step;
+
+	/*
+	 * 3. load instruction to be emulated into relevant register, and
+	 */
+	patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
+
+	/*
+	 * 4. branch back from trampoline
+	 */
+	buff[TMPL_RET_IDX] = create_branch((unsigned int *)buff + TMPL_RET_IDX,
+				(unsigned long)nip, 0);
+
+	flush_icache_range((unsigned long)buff,
+			   (unsigned long)(&buff[TMPL_END_IDX]));
+
+	op->optinsn.insn = buff;
+
+	return 0;
+}
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+	return optinsn->insn != NULL;
+}
+
+/*
+ * On powerpc, Optprobes always replaces one instruction (4 bytes
+ * aligned and 4 bytes long). It is impossible to encounter another
+ * kprobe in this 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;
+
+	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);
+		patch_instruction(op->kp.addr,
+			create_branch((unsigned int *)op->kp.addr,
+				      (unsigned long)op->optinsn.insn, 0));
+		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 ((unsigned long)op->kp.addr <= addr &&
+		(unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
+}
diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.S
new file mode 100644
index 0000000..c86976b
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes_head.S
@@ -0,0 +1,135 @@
+/*
+ * Code to prepare detour buffer for optprobes in Kernel.
+ *
+ * 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 <asm/ppc_asm.h>
+#include <asm/ptrace.h>
+#include <asm/asm-offsets.h>
+
+#define	OPT_SLOT_SIZE	65536
+
+	.balign	4
+
+	/*
+	 * Reserve an area to allocate slots for detour buffer.
+	 * This is part of .text section (rather than vmalloc area)
+	 * as this needs to be within 32MB of the probed address.
+	 */
+	.global optinsn_slot
+optinsn_slot:
+	.space	OPT_SLOT_SIZE
+
+	/*
+	 * Optprobe template:
+	 * This template gets copied into one of the slots in optinsn_slot
+	 * and gets fixed up with real optprobe structures et al.
+	 */
+	.global optprobe_template_entry
+optprobe_template_entry:
+	/* Create an in-memory pt_regs */
+	stdu	r1,-INT_FRAME_SIZE(r1)
+	SAVE_GPR(0,r1)
+	/* Save the previous SP into stack */
+	addi	r0,r1,INT_FRAME_SIZE
+	std	r0,GPR1(r1)
+	SAVE_10GPRS(2,r1)
+	SAVE_10GPRS(12,r1)
+	SAVE_10GPRS(22,r1)
+	/* Save SPRS */
+	mfmsr	r5
+	std	r5,_MSR(r1)
+	li	r5,0x700
+	std	r5,_TRAP(r1)
+	li	r5,0
+	std	r5,ORIG_GPR3(r1)
+	std	r5,RESULT(r1)
+	mfctr	r5
+	std	r5,_CTR(r1)
+	mflr	r5
+	std	r5,_LINK(r1)
+	mfspr	r5,SPRN_XER
+	std	r5,_XER(r1)
+	mfcr	r5
+	std	r5,_CCR(r1)
+	lbz     r5,PACASOFTIRQEN(r13)
+	std     r5,SOFTE(r1)
+	mfdar	r5
+	std	r5,_DAR(r1)
+	mfdsisr	r5
+	std	r5,_DSISR(r1)
+
+	.global optprobe_template_op_address
+optprobe_template_op_address:
+	/*
+	 * Parameters to optimized_callback():
+	 * 1. optimized_kprobe structure in r3
+	 */
+	nop
+	nop
+	nop
+	nop
+	nop
+	/* 2. pt_regs pointer in r4 */
+	addi	r4,r1,STACK_FRAME_OVERHEAD
+
+	.global optprobe_template_call_handler
+optprobe_template_call_handler:
+	/* Branch to optimized_callback() */
+	nop
+
+	/*
+	 * Parameters for instruction emulation:
+	 * 1. Pass SP in register r3.
+	 */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+
+	.global optprobe_template_insn
+optprobe_template_insn:
+	/* 2, Pass instruction to be emulated in r4 */
+	nop
+	nop
+
+	.global optprobe_template_call_emulate
+optprobe_template_call_emulate:
+	/* Branch to emulate_step()  */
+	nop
+
+	/*
+	 * All done.
+	 * Now, restore the registers...
+	 */
+	ld	r5,_MSR(r1)
+	mtmsr	r5
+	ld	r5,_CTR(r1)
+	mtctr	r5
+	ld	r5,_LINK(r1)
+	mtlr	r5
+	ld	r5,_XER(r1)
+	mtxer	r5
+	ld	r5,_CCR(r1)
+	mtcr	r5
+	ld	r5,_DAR(r1)
+	mtdar	r5
+	ld	r5,_DSISR(r1)
+	mtdsisr	r5
+	REST_GPR(0,r1)
+	REST_10GPRS(2,r1)
+	REST_10GPRS(12,r1)
+	REST_10GPRS(22,r1)
+	/* Restore the previous SP */
+	addi	r1,r1,INT_FRAME_SIZE
+
+	.global optprobe_template_ret
+optprobe_template_ret:
+	/* ... and jump back from trampoline */
+	nop
+
+	.global optprobe_template_end
+optprobe_template_end:
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 3362299..0c6c2b0 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -618,6 +618,27 @@ static int __kprobes trap_compare(long v1, long v2)
 }
 
 /*
+ * Helper to check if a given instruction is a conditional branch
+ * Derived from the conditional checks in analyse_instr()
+ */
+bool __kprobes is_conditional_branch(unsigned int instr)
+{
+	unsigned int opcode = instr >> 26;
+
+	if (opcode == 16)	/* bc, bca, bcl, bcla */
+		return true;
+	if (opcode == 19) {
+		switch ((instr >> 1) & 0x3ff) {
+		case 16:	/* bclr, bclrl */
+		case 528:	/* bcctr, bcctrl */
+		case 560:	/* bctar, bctarl */
+			return true;
+		}
+	}
+	return false;
+}
+
+/*
  * Elements of 32-bit rotate and mask instructions.
  */
 #define MASK32(mb, me)	((0xffffffffUL >> (mb)) + \
@@ -2018,3 +2039,4 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
 	regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
 	return 1;
 }
+
-- 
2.7.4