arch/powerpc/kernel/optprobes.c

   1 /*
   2  * Code for Kernel probes Jump optimization.
   3  *
   4  * Copyright 2017, Anju T, IBM Corp.
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/kprobes.h>
  13 #include <linux/jump_label.h>
  14 #include <linux/types.h>
  15 #include <linux/slab.h>
  16 #include <linux/list.h>
  17 #include <asm/kprobes.h>
  18 #include <asm/ptrace.h>
  19 #include <asm/cacheflush.h>
  20 #include <asm/code-patching.h>
  21 #include <asm/sstep.h>
  22 #include <asm/ppc-opcode.h>
  23
  24 #define TMPL_CALL_HDLR_IDX      \
  25         (optprobe_template_call_handler - optprobe_template_entry)
  26 #define TMPL_EMULATE_IDX        \
  27         (optprobe_template_call_emulate - optprobe_template_entry)
  28 #define TMPL_RET_IDX            \
  29         (optprobe_template_ret - optprobe_template_entry)
  30 #define TMPL_OP_IDX             \
  31         (optprobe_template_op_address - optprobe_template_entry)
  32 #define TMPL_INSN_IDX           \
  33         (optprobe_template_insn - optprobe_template_entry)
  34 #define TMPL_END_IDX            \
  35         (optprobe_template_end - optprobe_template_entry)
  36
  37 DEFINE_INSN_CACHE_OPS(ppc_optinsn);
  38
  39 static bool insn_page_in_use;
  40
  41 static void *__ppc_alloc_insn_page(void)
  42 {
  43         if (insn_page_in_use)
  44                 return NULL;
  45         insn_page_in_use = true;
  46         return &optinsn_slot;
  47 }
  48
  49 static void __ppc_free_insn_page(void *page __maybe_unused)
  50 {
  51         insn_page_in_use = false;
  52 }
  53
  54 struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
  55         .mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
  56         .pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
  57         /* insn_size initialized later */
  58         .alloc = __ppc_alloc_insn_page,
  59         .free = __ppc_free_insn_page,
  60         .nr_garbage = 0,
  61 };
  62
  63 /*
  64  * Check if we can optimize this probe. Returns NIP post-emulation if this can
  65  * be optimized and 0 otherwise.
  66  */
  67 static unsigned long can_optimize(struct kprobe *p)
  68 {
  69         struct pt_regs regs;
  70         struct instruction_op op;
  71         unsigned long nip = 0;
  72
  73         /*
  74          * kprobe placed for kretprobe during boot time
  75          * has a 'nop' instruction, which can be emulated.
  76          * So further checks can be skipped.
  77          */
  78         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
  79                 return (unsigned long)p->addr + sizeof(kprobe_opcode_t);
  80
  81         /*
  82          * We only support optimizing kernel addresses, but not
  83          * module addresses.
  84          *
  85          * FIXME: Optimize kprobes placed in module addresses.
  86          */
  87         if (!is_kernel_addr((unsigned long)p->addr))
  88                 return 0;
  89
  90         memset(&regs, 0, sizeof(struct pt_regs));
  91         regs.nip = (unsigned long)p->addr;
  92         regs.trap = 0x0;
  93         regs.msr = MSR_KERNEL;
  94
  95         /*
  96          * Kprobe placed in conditional branch instructions are
  97          * not optimized, as we can't predict the nip prior with
  98          * dummy pt_regs and can not ensure that the return branch
  99          * from detour buffer falls in the range of address (i.e 32MB).
 100          * A branch back from trampoline is set up in the detour buffer
 101          * to the nip returned by the analyse_instr() here.
 102          *
 103          * Ensure that the instruction is not a conditional branch,
 104          * and that can be emulated.
 105          */
 106         if (!is_conditional_branch(*p->ainsn.insn) &&
 107                         analyse_instr(&op, &regs, *p->ainsn.insn) == 1) {
 108                 emulate_update_regs(&regs, &op);
 109                 nip = regs.nip;
 110         }
 111
 112         return nip;
 113 }
 114
 115 static void optimized_callback(struct optimized_kprobe *op,
 116                                struct pt_regs *regs)
 117 {
 118         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 119         unsigned long flags;
 120
 121         /* This is possible if op is under delayed unoptimizing */
 122         if (kprobe_disabled(&op->kp))
 123                 return;
 124
 125         local_irq_save(flags);
 126         hard_irq_disable();
 127
 128         if (kprobe_running()) {
 129                 kprobes_inc_nmissed_count(&op->kp);
 130         } else {
 131                 __this_cpu_write(current_kprobe, &op->kp);
 132                 regs->nip = (unsigned long)op->kp.addr;
 133                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 134                 opt_pre_handler(&op->kp, regs);
 135                 __this_cpu_write(current_kprobe, NULL);
 136         }
 137
 138         /*
 139          * No need for an explicit __hard_irq_enable() here.
 140          * local_irq_restore() will re-enable interrupts,
 141          * if they were hard disabled.
 142          */
 143         local_irq_restore(flags);
 144 }
 145 NOKPROBE_SYMBOL(optimized_callback);
 146
 147 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 148 {
 149         if (op->optinsn.insn) {
 150                 free_ppc_optinsn_slot(op->optinsn.insn, 1);
 151                 op->optinsn.insn = NULL;
 152         }
 153 }
 154
 155 /*
 156  * emulate_step() requires insn to be emulated as
 157  * second parameter. Load register 'r4' with the
 158  * instruction.
 159  */
 160 void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
 161 {
 162         /* addis r4,0,(insn)@h */
 163         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(4) |
 164                           ((val >> 16) & 0xffff));
 165         addr++;
 166
 167         /* ori r4,r4,(insn)@l */
 168         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(4) |
 169                           ___PPC_RS(4) | (val & 0xffff));
 170 }
 171
 172 /*
 173  * Generate instructions to load provided immediate 64-bit value
 174  * to register 'r3' and patch these instructions at 'addr'.
 175  */
 176 void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
 177 {
 178         /* lis r3,(op)@highest */
 179         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(3) |
 180                           ((val >> 48) & 0xffff));
 181         addr++;
 182
 183         /* ori r3,r3,(op)@higher */
 184         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 185                           ___PPC_RS(3) | ((val >> 32) & 0xffff));
 186         addr++;
 187
 188         /* rldicr r3,r3,32,31 */
 189         patch_instruction(addr, PPC_INST_RLDICR | ___PPC_RA(3) |
 190                           ___PPC_RS(3) | __PPC_SH64(32) | __PPC_ME64(31));
 191         addr++;
 192
 193         /* oris r3,r3,(op)@h */
 194         patch_instruction(addr, PPC_INST_ORIS | ___PPC_RA(3) |
 195                           ___PPC_RS(3) | ((val >> 16) & 0xffff));
 196         addr++;
 197
 198         /* ori r3,r3,(op)@l */
 199         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 200                           ___PPC_RS(3) | (val & 0xffff));
 201 }
 202
 203 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 204 {
 205         kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
 206         kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
 207         long b_offset;
 208         unsigned long nip, size;
 209         int rc, i;
 210
 211         kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 212
 213         nip = can_optimize(p);
 214         if (!nip)
 215                 return -EILSEQ;
 216
 217         /* Allocate instruction slot for detour buffer */
 218         buff = get_ppc_optinsn_slot();
 219         if (!buff)
 220                 return -ENOMEM;
 221
 222         /*
 223          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 224          *
 225          * The target address has to be relatively nearby, to permit use
 226          * of branch instruction in powerpc, because the address is specified
 227          * in an immediate field in the instruction opcode itself, ie 24 bits
 228          * in the opcode specify the address. Therefore the address should
 229          * be within 32MB on either side of the current instruction.
 230          */
 231         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 232         if (!is_offset_in_branch_range(b_offset))
 233                 goto error;
 234
 235         /* Check if the return address is also within 32MB range */
 236         b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
 237                         (unsigned long)nip;
 238         if (!is_offset_in_branch_range(b_offset))
 239                 goto error;
 240
 241         /* Setup template */
 242         /* We can optimize this via patch_instruction_window later */
 243         size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
 244         pr_devel("Copying template to %p, size %lu\n", buff, size);
 245         for (i = 0; i < size; i++) {
 246                 rc = patch_instruction(buff + i, *(optprobe_template_entry + i));
 247                 if (rc < 0)
 248                         goto error;
 249         }
 250
 251         /*
 252          * Fixup the template with instructions to:
 253          * 1. load the address of the actual probepoint
 254          */
 255         patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
 256
 257         /*
 258          * 2. branch to optimized_callback() and emulate_step()
 259          */
 260         op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
 261         emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
 262         if (!op_callback_addr || !emulate_step_addr) {
 263                 WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 264                 goto error;
 265         }
 266
 267         branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
 268                                 (unsigned long)op_callback_addr,
 269                                 BRANCH_SET_LINK);
 270
 271         branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
 272                                 (unsigned long)emulate_step_addr,
 273                                 BRANCH_SET_LINK);
 274
 275         if (!branch_op_callback || !branch_emulate_step)
 276                 goto error;
 277
 278         patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
 279         patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);
 280
 281         /*
 282          * 3. load instruction to be emulated into relevant register, and
 283          */
 284         patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
 285
 286         /*
 287          * 4. branch back from trampoline
 288          */
 289         patch_branch(buff + TMPL_RET_IDX, (unsigned long)nip, 0);
 290
 291         flush_icache_range((unsigned long)buff,
 292                            (unsigned long)(&buff[TMPL_END_IDX]));
 293
 294         op->optinsn.insn = buff;
 295
 296         return 0;
 297
 298 error:
 299         free_ppc_optinsn_slot(buff, 0);
 300         return -ERANGE;
 301
 302 }
 303
 304 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 305 {
 306         return optinsn->insn != NULL;
 307 }
 308
 309 /*
 310  * On powerpc, Optprobes always replaces one instruction (4 bytes
 311  * aligned and 4 bytes long). It is impossible to encounter another
 312  * kprobe in this address range. So always return 0.
 313  */
 314 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 315 {
 316         return 0;
 317 }
 318
 319 void arch_optimize_kprobes(struct list_head *oplist)
 320 {
 321         struct optimized_kprobe *op;
 322         struct optimized_kprobe *tmp;
 323
 324         list_for_each_entry_safe(op, tmp, oplist, list) {
 325                 /*
 326                  * Backup instructions which will be replaced
 327                  * by jump address
 328                  */
 329                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 330                                                RELATIVEJUMP_SIZE);
 331                 patch_instruction(op->kp.addr,
 332                         create_branch((unsigned int *)op->kp.addr,
 333                                       (unsigned long)op->optinsn.insn, 0));
 334                 list_del_init(&op->list);
 335         }
 336 }
 337
 338 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 339 {
 340         arch_arm_kprobe(&op->kp);
 341 }
 342
 343 void arch_unoptimize_kprobes(struct list_head *oplist,
 344                              struct list_head *done_list)
 345 {
 346         struct optimized_kprobe *op;
 347         struct optimized_kprobe *tmp;
 348
 349         list_for_each_entry_safe(op, tmp, oplist, list) {
 350                 arch_unoptimize_kprobe(op);
 351                 list_move(&op->list, done_list);
 352         }
 353 }
 354
 355 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 356                                  unsigned long addr)
 357 {
 358         return ((unsigned long)op->kp.addr <= addr &&
 359                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 360 }