[PATCH v4 1/2] arch/powerpc: Implement Optprobes

From: Anju T Sudhakar
Date: Wed Feb 08 2017 - 04:51:36 EST

Current infrastructure of kprobe uses the unconditional trap instruction
to probe a running kernel. Optprobe allows kprobe to replace the trap with
a branch instruction to a detour buffer. Detour buffer contains instructions
to create an in memory pt_regs. Detour buffer also has a call to
optimized_callback() which in turn call the pre_handler().
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.

To address the limitation of branch instruction in POWER architecture,
detour buffer slot is allocated from a reserved area. For the time being,
64KB is reserved in memory for this purpose.

Instructions which can be emulated using analyse_instr() are the candidates
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>
Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/code-patching.h | 1 +
arch/powerpc/include/asm/kprobes.h | 24 ++-
arch/powerpc/kernel/Makefile | 1 +
arch/powerpc/kernel/optprobes.c | 348 +++++++++++++++++++++++++++++++
arch/powerpc/kernel/optprobes_head.S | 135 ++++++++++++
arch/powerpc/lib/code-patching.c | 21 ++
7 files changed, 530 insertions(+), 1 deletion(-)
create mode 100644 arch/powerpc/kernel/optprobes.c
create mode 100644 arch/powerpc/kernel/optprobes_head.S

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a8ee573..e4d352e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -99,6 +99,7 @@ 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/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 75ee4f4..8ab9377 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -35,6 +35,7 @@ int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr);
unsigned long branch_target(const unsigned int *instr);
unsigned int translate_branch(const unsigned int *dest,
const unsigned int *src);
+extern bool is_conditional_branch(unsigned int instr);
#ifdef CONFIG_PPC_BOOK3E_64
void __patch_exception(int exc, unsigned long addr);
#define patch_exception(exc, name) do { \
diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index 77885d8..d821835 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -40,7 +40,23 @@ 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[];
+
+/* Fixed instruction size for powerpc */
+#define MAX_INSN_SIZE 1
+#define MAX_OPTIMIZED_LENGTH sizeof(kprobe_opcode_t) /* 4 bytes */
+#define MAX_OPTINSN_SIZE (optprobe_template_end - optprobe_template_entry)
+#define RELATIVEJUMP_SIZE sizeof(kprobe_opcode_t) /* 4 bytes */

#ifdef PPC64_ELF_ABI_v2
/* PPC64 ABIv2 needs local entry point */
@@ -126,6 +142,12 @@ 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/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 23f8082..ff0eef5 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -100,6 +100,7 @@ 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..b569e08
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,348 @@
+/*
+ * Code for Kernel probes Jump optimization.
+ *
+ * Copyright 2017, 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.
+ *
+ * FIXME: Optimize kprobes placed in module addresses.
+ */
+ if (!is_kernel_addr((unsigned long)p->addr))
+ return 0;
+
+ memset(&regs, 0, sizeof(struct pt_regs));
+ regs.nip = (unsigned long)p->addr;
+ regs.trap = 0x0;
+ regs.msr = MSR_KERNEL;
+
+ /*
+ * Kprobe placed in conditional branch instructions are
+ * not optimized, as we can't predict the nip prior with
+ * dummy pt_regs and can not ensure that the return branch
+ * from detour buffer falls in the range of address (i.e 32MB).
+ * A branch back from trampoline is set up in the detour buffer
+ * to the nip returned by the analyse_instr() here.
+ *
+ * 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);
+ hard_irq_disable();
+
+ 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);
+ }
+
+ /*
+ * No need for an explicit __hard_irq_enable() here.
+ * local_irq_restore() will re-enable interrupts,
+ * if they were hard disabled.
+ */
+ 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))
+ goto error;
+
+ /* 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))
+ goto error;
+
+ /* 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) {
+ WARN(1, "kprobe_lookup_name() failed\n");
+ goto error;
+ }
+
+ 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)
+ goto error;
+
+ 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;
+
+ error:
+ free_ppc_optinsn_slot(buff, 0);
+ return -ERANGE;
+
+}
+
+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..53e429b
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes_head.S
@@ -0,0 +1,135 @@
+/*
+ * Code to prepare detour buffer for optprobes in Kernel.
+ *
+ * Copyright 2017, 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/code-patching.c b/arch/powerpc/lib/code-patching.c
index 4ccf16a..0899315 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -54,6 +54,27 @@ bool is_offset_in_branch_range(long offset)
return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
}

+/*
+ * 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;
+}
+
unsigned int create_branch(const unsigned int *addr,
unsigned long target, int flags)
{
--
2.7.4