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         /* This is possible if op is under delayed unoptimizing */
 119         if (kprobe_disabled(&op->kp))
 120                 return;
 121
 122         preempt_disable();
 123
 124         if (kprobe_running()) {
 125                 kprobes_inc_nmissed_count(&op->kp);
 126         } else {
 127                 __this_cpu_write(current_kprobe, &op->kp);
 128                 regs->nip = (unsigned long)op->kp.addr;
 129                 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 130                 opt_pre_handler(&op->kp, regs);
 131                 __this_cpu_write(current_kprobe, NULL);
 132         }
 133
 134         preempt_enable_no_resched();
 135 }
 136 NOKPROBE_SYMBOL(optimized_callback);
 137
 138 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 139 {
 140         if (op->optinsn.insn) {
 141                 free_ppc_optinsn_slot(op->optinsn.insn, 1);
 142                 op->optinsn.insn = NULL;
 143         }
 144 }
 145
 146 /*
 147  * emulate_step() requires insn to be emulated as
 148  * second parameter. Load register 'r4' with the
 149  * instruction.
 150  */
 151 void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
 152 {
 153         /* addis r4,0,(insn)@h */
 154         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(4) |
 155                           ((val >> 16) & 0xffff));
 156         addr++;
 157
 158         /* ori r4,r4,(insn)@l */
 159         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(4) |
 160                           ___PPC_RS(4) | (val & 0xffff));
 161 }
 162
 163 /*
 164  * Generate instructions to load provided immediate 64-bit value
 165  * to register 'r3' and patch these instructions at 'addr'.
 166  */
 167 void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
 168 {
 169         /* lis r3,(op)@highest */
 170         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(3) |
 171                           ((val >> 48) & 0xffff));
 172         addr++;
 173
 174         /* ori r3,r3,(op)@higher */
 175         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 176                           ___PPC_RS(3) | ((val >> 32) & 0xffff));
 177         addr++;
 178
 179         /* rldicr r3,r3,32,31 */
 180         patch_instruction(addr, PPC_INST_RLDICR | ___PPC_RA(3) |
 181                           ___PPC_RS(3) | __PPC_SH64(32) | __PPC_ME64(31));
 182         addr++;
 183
 184         /* oris r3,r3,(op)@h */
 185         patch_instruction(addr, PPC_INST_ORIS | ___PPC_RA(3) |
 186                           ___PPC_RS(3) | ((val >> 16) & 0xffff));
 187         addr++;
 188
 189         /* ori r3,r3,(op)@l */
 190         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 191                           ___PPC_RS(3) | (val & 0xffff));
 192 }
 193
 194 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 195 {
 196         kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
 197         kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
 198         long b_offset;
 199         unsigned long nip, size;
 200         int rc, i;
 201
 202         kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 203
 204         nip = can_optimize(p);
 205         if (!nip)
 206                 return -EILSEQ;
 207
 208         /* Allocate instruction slot for detour buffer */
 209         buff = get_ppc_optinsn_slot();
 210         if (!buff)
 211                 return -ENOMEM;
 212
 213         /*
 214          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 215          *
 216          * The target address has to be relatively nearby, to permit use
 217          * of branch instruction in powerpc, because the address is specified
 218          * in an immediate field in the instruction opcode itself, ie 24 bits
 219          * in the opcode specify the address. Therefore the address should
 220          * be within 32MB on either side of the current instruction.
 221          */
 222         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 223         if (!is_offset_in_branch_range(b_offset))
 224                 goto error;
 225
 226         /* Check if the return address is also within 32MB range */
 227         b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
 228                         (unsigned long)nip;
 229         if (!is_offset_in_branch_range(b_offset))
 230                 goto error;
 231
 232         /* Setup template */
 233         /* We can optimize this via patch_instruction_window later */
 234         size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
 235         pr_devel("Copying template to %p, size %lu\n", buff, size);
 236         for (i = 0; i < size; i++) {
 237                 rc = patch_instruction(buff + i, *(optprobe_template_entry + i));
 238                 if (rc < 0)
 239                         goto error;
 240         }
 241
 242         /*
 243          * Fixup the template with instructions to:
 244          * 1. load the address of the actual probepoint
 245          */
 246         patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
 247
 248         /*
 249          * 2. branch to optimized_callback() and emulate_step()
 250          */
 251         op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
 252         emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
 253         if (!op_callback_addr || !emulate_step_addr) {
 254                 WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 255                 goto error;
 256         }
 257
 258         branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
 259                                 (unsigned long)op_callback_addr,
 260                                 BRANCH_SET_LINK);
 261
 262         branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
 263                                 (unsigned long)emulate_step_addr,
 264                                 BRANCH_SET_LINK);
 265
 266         if (!branch_op_callback || !branch_emulate_step)
 267                 goto error;
 268
 269         patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
 270         patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);
 271
 272         /*
 273          * 3. load instruction to be emulated into relevant register, and
 274          */
 275         patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
 276
 277         /*
 278          * 4. branch back from trampoline
 279          */
 280         patch_branch(buff + TMPL_RET_IDX, (unsigned long)nip, 0);
 281
 282         flush_icache_range((unsigned long)buff,
 283                            (unsigned long)(&buff[TMPL_END_IDX]));
 284
 285         op->optinsn.insn = buff;
 286
 287         return 0;
 288
 289 error:
 290         free_ppc_optinsn_slot(buff, 0);
 291         return -ERANGE;
 292
 293 }
 294
 295 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 296 {
 297         return optinsn->insn != NULL;
 298 }
 299
 300 /*
 301  * On powerpc, Optprobes always replaces one instruction (4 bytes
 302  * aligned and 4 bytes long). It is impossible to encounter another
 303  * kprobe in this address range. So always return 0.
 304  */
 305 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 306 {
 307         return 0;
 308 }
 309
 310 void arch_optimize_kprobes(struct list_head *oplist)
 311 {
 312         struct optimized_kprobe *op;
 313         struct optimized_kprobe *tmp;
 314
 315         list_for_each_entry_safe(op, tmp, oplist, list) {
 316                 /*
 317                  * Backup instructions which will be replaced
 318                  * by jump address
 319                  */
 320                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 321                                                RELATIVEJUMP_SIZE);
 322                 patch_instruction(op->kp.addr,
 323                         create_branch((unsigned int *)op->kp.addr,
 324                                       (unsigned long)op->optinsn.insn, 0));
 325                 list_del_init(&op->list);
 326         }
 327 }
 328
 329 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 330 {
 331         arch_arm_kprobe(&op->kp);
 332 }
 333
 334 void arch_unoptimize_kprobes(struct list_head *oplist,
 335                              struct list_head *done_list)
 336 {
 337         struct optimized_kprobe *op;
 338         struct optimized_kprobe *tmp;
 339
 340         list_for_each_entry_safe(op, tmp, oplist, list) {
 341                 arch_unoptimize_kprobe(op);
 342                 list_move(&op->list, done_list);
 343         }
 344 }
 345
 346 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 347                                  unsigned long addr)
 348 {
 349         return ((unsigned long)op->kp.addr <= addr &&
 350                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 351 }