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<p>Hi Masami,</p>
<p><br>
</p>
<p>Thank you for reviewing the patch.<br>
</p>
<br>
<div class="moz-cite-prefix">On Thursday 08 September 2016 10:17 PM,
Masami Hiramatsu wrote:<br>
</div>
<blockquote
cite="mid:20160909014701.8d59bdb341a19a9f98f7ee64@kernel.org"
type="cite">
<pre wrap="">On Wed, 7 Sep 2016 15:03:11 +0530
Anju T Sudhakar <a class="moz-txt-link-rfc2396E" href="mailto:anju@linux.vnet.ibm.com"><anju@linux.vnet.ibm.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">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 <a class="moz-txt-link-rfc2396E" href="mailto:anju@linux.vnet.ibm.com"><anju@linux.vnet.ibm.com></a>
---
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;
</pre>
</blockquote>
<pre wrap="">
Could you free regs here? Or allocate it on stack.</pre>
</blockquote>
<br>
yes. 'regs' can be freed here.<br>
<blockquote
cite="mid:20160909014701.8d59bdb341a19a9f98f7ee64@kernel.org"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">+}
+
+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);
</pre>
</blockquote>
<pre wrap="">
This doesn't work because op->optinsn.insn is NULL here. (buff is assigned
at the end of this function)
</pre>
</blockquote>
<br>
yes. You are right. Need to free 'buff' here. <br>
Thank you for pointing out this.<br>
<blockquote
cite="mid:20160909014701.8d59bdb341a19a9f98f7ee64@kernel.org"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">+ 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);
</pre>
</blockquote>
<pre wrap="">
ditto.
</pre>
<blockquote type="cite">
<pre wrap="">+ 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;
</pre>
</blockquote>
<pre wrap="">
Hmm, wouldn't we have to use patch_instruction() here?
(It seems ppc kprobe implementation should also be updated to use it...)</pre>
</blockquote>
<blockquote
cite="mid:20160909014701.8d59bdb341a19a9f98f7ee64@kernel.org"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">+ 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;
</pre>
</blockquote>
<pre wrap="">
Here, please check the address range as same as arm32 optprobe implementation.
e.g.
return ((unsigned long)op->kp.addr <= addr &&
(unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
Thank you,
</pre>
</blockquote>
<br>
Do we really need this? <font size="+2"><font size="+1">The only
case this check will succeed is if kp.addr is not a multiple of
4, which is not a valid address at all on</font></font><font
size="+2"><font size="+1"> Power. So should we again check here
for that</font>?<br>
<br>
<br>
</font><br>
Thanks and regards<br>
-Anju<font size="+2"><br>
</font>
<blockquote
cite="mid:20160909014701.8d59bdb341a19a9f98f7ee64@kernel.org"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">+}
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
</pre>
</blockquote>
<pre wrap="">
</pre>
</blockquote>
<br>
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