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))
 108                 nip = regs.nip;
 109
 110         return nip;
 111 }
 112
 113 static void optimized_callback(struct optimized_kprobe *op,
 114                                struct pt_regs *regs)
 115 {
 116         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 117         unsigned long flags;
 118
 119         /* This is possible if op is under delayed unoptimizing */
 120         if (kprobe_disabled(&op->kp))
 121                 return;
 122
 123         local_irq_save(flags);
 124         hard_irq_disable();
 125
 126         if (kprobe_running()) {
 127                 kprobes_inc_nmissed_count(&op->kp);
 128         } else {
 129                 __this_cpu_write(current_kprobe, &op->kp);
 130                 regs->nip = (unsigned long)op->kp.addr;
 131                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 132                 opt_pre_handler(&op->kp, regs);
 133                 __this_cpu_write(current_kprobe, NULL);
 134         }
 135
 136         /*
 137          * No need for an explicit __hard_irq_enable() here.
 138          * local_irq_restore() will re-enable interrupts,
 139          * if they were hard disabled.
 140          */
 141         local_irq_restore(flags);
 142 }
 143 NOKPROBE_SYMBOL(optimized_callback);
 144
 145 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 146 {
 147         if (op->optinsn.insn) {
 148                 free_ppc_optinsn_slot(op->optinsn.insn, 1);
 149                 op->optinsn.insn = NULL;
 150         }
 151 }
 152
 153 /*
 154  * emulate_step() requires insn to be emulated as
 155  * second parameter. Load register 'r4' with the
 156  * instruction.
 157  */
 158 void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
 159 {
 160         /* addis r4,0,(insn)@h */
 161         *addr++ = PPC_INST_ADDIS | ___PPC_RT(4) |
 162                   ((val >> 16) & 0xffff);
 163
 164         /* ori r4,r4,(insn)@l */
 165         *addr = PPC_INST_ORI | ___PPC_RA(4) | ___PPC_RS(4) |
 166                 (val & 0xffff);
 167 }
 168
 169 /*
 170  * Generate instructions to load provided immediate 64-bit value
 171  * to register 'r3' and patch these instructions at 'addr'.
 172  */
 173 void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
 174 {
 175         /* lis r3,(op)@highest */
 176         *addr++ = PPC_INST_ADDIS | ___PPC_RT(3) |
 177                   ((val >> 48) & 0xffff);
 178
 179         /* ori r3,r3,(op)@higher */
 180         *addr++ = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
 181                   ((val >> 32) & 0xffff);
 182
 183         /* rldicr r3,r3,32,31 */
 184         *addr++ = PPC_INST_RLDICR | ___PPC_RA(3) | ___PPC_RS(3) |
 185                   __PPC_SH64(32) | __PPC_ME64(31);
 186
 187         /* oris r3,r3,(op)@h */
 188         *addr++ = PPC_INST_ORIS | ___PPC_RA(3) | ___PPC_RS(3) |
 189                   ((val >> 16) & 0xffff);
 190
 191         /* ori r3,r3,(op)@l */
 192         *addr = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
 193                 (val & 0xffff);
 194 }
 195
 196 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 197 {
 198         kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
 199         kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
 200         long b_offset;
 201         unsigned long nip;
 202
 203         kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 204
 205         nip = can_optimize(p);
 206         if (!nip)
 207                 return -EILSEQ;
 208
 209         /* Allocate instruction slot for detour buffer */
 210         buff = get_ppc_optinsn_slot();
 211         if (!buff)
 212                 return -ENOMEM;
 213
 214         /*
 215          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 216          *
 217          * The target address has to be relatively nearby, to permit use
 218          * of branch instruction in powerpc, because the address is specified
 219          * in an immediate field in the instruction opcode itself, ie 24 bits
 220          * in the opcode specify the address. Therefore the address should
 221          * be within 32MB on either side of the current instruction.
 222          */
 223         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 224         if (!is_offset_in_branch_range(b_offset))
 225                 goto error;
 226
 227         /* Check if the return address is also within 32MB range */
 228         b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
 229                         (unsigned long)nip;
 230         if (!is_offset_in_branch_range(b_offset))
 231                 goto error;
 232
 233         /* Setup template */
 234         memcpy(buff, optprobe_template_entry,
 235                         TMPL_END_IDX * sizeof(kprobe_opcode_t));
 236
 237         /*
 238          * Fixup the template with instructions to:
 239          * 1. load the address of the actual probepoint
 240          */
 241         patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
 242
 243         /*
 244          * 2. branch to optimized_callback() and emulate_step()
 245          */
 246         kprobe_lookup_name("optimized_callback", op_callback_addr);
 247         kprobe_lookup_name("emulate_step", emulate_step_addr);
 248         if (!op_callback_addr || !emulate_step_addr) {
 249                 WARN(1, "kprobe_lookup_name() failed\n");
 250                 goto error;
 251         }
 252
 253         branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
 254                                 (unsigned long)op_callback_addr,
 255                                 BRANCH_SET_LINK);
 256
 257         branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
 258                                 (unsigned long)emulate_step_addr,
 259                                 BRANCH_SET_LINK);
 260
 261         if (!branch_op_callback || !branch_emulate_step)
 262                 goto error;
 263
 264         buff[TMPL_CALL_HDLR_IDX] = branch_op_callback;
 265         buff[TMPL_EMULATE_IDX] = branch_emulate_step;
 266
 267         /*
 268          * 3. load instruction to be emulated into relevant register, and
 269          */
 270         patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
 271
 272         /*
 273          * 4. branch back from trampoline
 274          */
 275         buff[TMPL_RET_IDX] = create_branch((unsigned int *)buff + TMPL_RET_IDX,
 276                                 (unsigned long)nip, 0);
 277
 278         flush_icache_range((unsigned long)buff,
 279                            (unsigned long)(&buff[TMPL_END_IDX]));
 280
 281         op->optinsn.insn = buff;
 282
 283         return 0;
 284
 285 error:
 286         free_ppc_optinsn_slot(buff, 0);
 287         return -ERANGE;
 288
 289 }
 290
 291 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 292 {
 293         return optinsn->insn != NULL;
 294 }
 295
 296 /*
 297  * On powerpc, Optprobes always replaces one instruction (4 bytes
 298  * aligned and 4 bytes long). It is impossible to encounter another
 299  * kprobe in this address range. So always return 0.
 300  */
 301 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 302 {
 303         return 0;
 304 }
 305
 306 void arch_optimize_kprobes(struct list_head *oplist)
 307 {
 308         struct optimized_kprobe *op;
 309         struct optimized_kprobe *tmp;
 310
 311         list_for_each_entry_safe(op, tmp, oplist, list) {
 312                 /*
 313                  * Backup instructions which will be replaced
 314                  * by jump address
 315                  */
 316                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 317                                                RELATIVEJUMP_SIZE);
 318                 patch_instruction(op->kp.addr,
 319                         create_branch((unsigned int *)op->kp.addr,
 320                                       (unsigned long)op->optinsn.insn, 0));
 321                 list_del_init(&op->list);
 322         }
 323 }
 324
 325 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 326 {
 327         arch_arm_kprobe(&op->kp);
 328 }
 329
 330 void arch_unoptimize_kprobes(struct list_head *oplist,
 331                              struct list_head *done_list)
 332 {
 333         struct optimized_kprobe *op;
 334         struct optimized_kprobe *tmp;
 335
 336         list_for_each_entry_safe(op, tmp, oplist, list) {
 337                 arch_unoptimize_kprobe(op);
 338                 list_move(&op->list, done_list);
 339         }
 340 }
 341
 342 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 343                                  unsigned long addr)
 344 {
 345         return ((unsigned long)op->kp.addr <= addr &&
 346                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 347 }