arch/powerpc/kernel/optprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Code for Kernel probes Jump optimization.
   4  *
   5  * Copyright 2017, Anju T, IBM Corp.
   6  */
   7
   8 #include <linux/kprobes.h>
   9 #include <linux/jump_label.h>
  10 #include <linux/types.h>
  11 #include <linux/slab.h>
  12 #include <linux/list.h>
  13 #include <asm/kprobes.h>
  14 #include <asm/ptrace.h>
  15 #include <asm/cacheflush.h>
  16 #include <asm/code-patching.h>
  17 #include <asm/sstep.h>
  18 #include <asm/ppc-opcode.h>
  19 #include <asm/inst.h>
  20
  21 #define TMPL_CALL_HDLR_IDX      \
  22         (optprobe_template_call_handler - optprobe_template_entry)
  23 #define TMPL_EMULATE_IDX        \
  24         (optprobe_template_call_emulate - optprobe_template_entry)
  25 #define TMPL_RET_IDX            \
  26         (optprobe_template_ret - optprobe_template_entry)
  27 #define TMPL_OP_IDX             \
  28         (optprobe_template_op_address - optprobe_template_entry)
  29 #define TMPL_INSN_IDX           \
  30         (optprobe_template_insn - optprobe_template_entry)
  31 #define TMPL_END_IDX            \
  32         (optprobe_template_end - optprobe_template_entry)
  33
  34 DEFINE_INSN_CACHE_OPS(ppc_optinsn);
  35
  36 static bool insn_page_in_use;
  37
  38 static void *__ppc_alloc_insn_page(void)
  39 {
  40         if (insn_page_in_use)
  41                 return NULL;
  42         insn_page_in_use = true;
  43         return &optinsn_slot;
  44 }
  45
  46 static void __ppc_free_insn_page(void *page __maybe_unused)
  47 {
  48         insn_page_in_use = false;
  49 }
  50
  51 struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
  52         .mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
  53         .pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
  54         /* insn_size initialized later */
  55         .alloc = __ppc_alloc_insn_page,
  56         .free = __ppc_free_insn_page,
  57         .nr_garbage = 0,
  58 };
  59
  60 /*
  61  * Check if we can optimize this probe. Returns NIP post-emulation if this can
  62  * be optimized and 0 otherwise.
  63  */
  64 static unsigned long can_optimize(struct kprobe *p)
  65 {
  66         struct pt_regs regs;
  67         struct instruction_op op;
  68         unsigned long nip = 0;
  69
  70         /*
  71          * kprobe placed for kretprobe during boot time
  72          * has a 'nop' instruction, which can be emulated.
  73          * So further checks can be skipped.
  74          */
  75         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
  76                 return (unsigned long)p->addr + sizeof(kprobe_opcode_t);
  77
  78         /*
  79          * We only support optimizing kernel addresses, but not
  80          * module addresses.
  81          *
  82          * FIXME: Optimize kprobes placed in module addresses.
  83          */
  84         if (!is_kernel_addr((unsigned long)p->addr))
  85                 return 0;
  86
  87         memset(&regs, 0, sizeof(struct pt_regs));
  88         regs.nip = (unsigned long)p->addr;
  89         regs.trap = 0x0;
  90         regs.msr = MSR_KERNEL;
  91
  92         /*
  93          * Kprobe placed in conditional branch instructions are
  94          * not optimized, as we can't predict the nip prior with
  95          * dummy pt_regs and can not ensure that the return branch
  96          * from detour buffer falls in the range of address (i.e 32MB).
  97          * A branch back from trampoline is set up in the detour buffer
  98          * to the nip returned by the analyse_instr() here.
  99          *
 100          * Ensure that the instruction is not a conditional branch,
 101          * and that can be emulated.
 102          */
 103         if (!is_conditional_branch(ppc_inst_read((struct ppc_inst *)p->ainsn.insn)) &&
 104             analyse_instr(&op, &regs,
 105                           ppc_inst_read((struct ppc_inst *)p->ainsn.insn)) == 1) {
 106                 emulate_update_regs(&regs, &op);
 107                 nip = regs.nip;
 108         }
 109
 110         return nip;
 111 }
 112
 113 static void optimized_callback(struct optimized_kprobe *op,
 114                                struct pt_regs *regs)
 115 {
 116         /* This is possible if op is under delayed unoptimizing */
 117         if (kprobe_disabled(&op->kp))
 118                 return;
 119
 120         preempt_disable();
 121
 122         if (kprobe_running()) {
 123                 kprobes_inc_nmissed_count(&op->kp);
 124         } else {
 125                 __this_cpu_write(current_kprobe, &op->kp);
 126                 regs->nip = (unsigned long)op->kp.addr;
 127                 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 128                 opt_pre_handler(&op->kp, regs);
 129                 __this_cpu_write(current_kprobe, NULL);
 130         }
 131
 132         preempt_enable_no_resched();
 133 }
 134 NOKPROBE_SYMBOL(optimized_callback);
 135
 136 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 137 {
 138         if (op->optinsn.insn) {
 139                 free_ppc_optinsn_slot(op->optinsn.insn, 1);
 140                 op->optinsn.insn = NULL;
 141         }
 142 }
 143
 144 /*
 145  * emulate_step() requires insn to be emulated as
 146  * second parameter. Load register 'r4' with the
 147  * instruction.
 148  */
 149 void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
 150 {
 151         /* addis r4,0,(insn)@h */
 152         patch_instruction((struct ppc_inst *)addr,
 153                           ppc_inst(PPC_INST_ADDIS | ___PPC_RT(4) |
 154                                    ((val >> 16) & 0xffff)));
 155         addr++;
 156
 157         /* ori r4,r4,(insn)@l */
 158         patch_instruction((struct ppc_inst *)addr,
 159                           ppc_inst(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 'reg' and patch these instructions at 'addr'.
 166  */
 167 void patch_imm64_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
 168 {
 169         /* lis reg,(op)@highest */
 170         patch_instruction((struct ppc_inst *)addr,
 171                           ppc_inst(PPC_INST_ADDIS | ___PPC_RT(reg) |
 172                                    ((val >> 48) & 0xffff)));
 173         addr++;
 174
 175         /* ori reg,reg,(op)@higher */
 176         patch_instruction((struct ppc_inst *)addr,
 177                           ppc_inst(PPC_INST_ORI | ___PPC_RA(reg) |
 178                                    ___PPC_RS(reg) | ((val >> 32) & 0xffff)));
 179         addr++;
 180
 181         /* rldicr reg,reg,32,31 */
 182         patch_instruction((struct ppc_inst *)addr,
 183                           ppc_inst(PPC_INST_RLDICR | ___PPC_RA(reg) |
 184                                    ___PPC_RS(reg) | __PPC_SH64(32) | __PPC_ME64(31)));
 185         addr++;
 186
 187         /* oris reg,reg,(op)@h */
 188         patch_instruction((struct ppc_inst *)addr,
 189                           ppc_inst(PPC_INST_ORIS | ___PPC_RA(reg) |
 190                                    ___PPC_RS(reg) | ((val >> 16) & 0xffff)));
 191         addr++;
 192
 193         /* ori reg,reg,(op)@l */
 194         patch_instruction((struct ppc_inst *)addr,
 195                           ppc_inst(PPC_INST_ORI | ___PPC_RA(reg) |
 196                                    ___PPC_RS(reg) | (val & 0xffff)));
 197 }
 198
 199 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 200 {
 201         struct ppc_inst branch_op_callback, branch_emulate_step, temp;
 202         kprobe_opcode_t *op_callback_addr, *emulate_step_addr, *buff;
 203         long b_offset;
 204         unsigned long nip, size;
 205         int rc, i;
 206
 207         kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 208
 209         nip = can_optimize(p);
 210         if (!nip)
 211                 return -EILSEQ;
 212
 213         /* Allocate instruction slot for detour buffer */
 214         buff = get_ppc_optinsn_slot();
 215         if (!buff)
 216                 return -ENOMEM;
 217
 218         /*
 219          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 220          *
 221          * The target address has to be relatively nearby, to permit use
 222          * of branch instruction in powerpc, because the address is specified
 223          * in an immediate field in the instruction opcode itself, ie 24 bits
 224          * in the opcode specify the address. Therefore the address should
 225          * be within 32MB on either side of the current instruction.
 226          */
 227         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 228         if (!is_offset_in_branch_range(b_offset))
 229                 goto error;
 230
 231         /* Check if the return address is also within 32MB range */
 232         b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
 233                         (unsigned long)nip;
 234         if (!is_offset_in_branch_range(b_offset))
 235                 goto error;
 236
 237         /* Setup template */
 238         /* We can optimize this via patch_instruction_window later */
 239         size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
 240         pr_devel("Copying template to %p, size %lu\n", buff, size);
 241         for (i = 0; i < size; i++) {
 242                 rc = patch_instruction((struct ppc_inst *)(buff + i),
 243                                        ppc_inst(*(optprobe_template_entry + i)));
 244                 if (rc < 0)
 245                         goto error;
 246         }
 247
 248         /*
 249          * Fixup the template with instructions to:
 250          * 1. load the address of the actual probepoint
 251          */
 252         patch_imm64_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
 253
 254         /*
 255          * 2. branch to optimized_callback() and emulate_step()
 256          */
 257         op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
 258         emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
 259         if (!op_callback_addr || !emulate_step_addr) {
 260                 WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 261                 goto error;
 262         }
 263
 264         rc = create_branch(&branch_op_callback,
 265                            (struct ppc_inst *)(buff + TMPL_CALL_HDLR_IDX),
 266                            (unsigned long)op_callback_addr,
 267                            BRANCH_SET_LINK);
 268
 269         rc |= create_branch(&branch_emulate_step,
 270                             (struct ppc_inst *)(buff + TMPL_EMULATE_IDX),
 271                             (unsigned long)emulate_step_addr,
 272                             BRANCH_SET_LINK);
 273
 274         if (rc)
 275                 goto error;
 276
 277         patch_instruction((struct ppc_inst *)(buff + TMPL_CALL_HDLR_IDX),
 278                           branch_op_callback);
 279         patch_instruction((struct ppc_inst *)(buff + TMPL_EMULATE_IDX),
 280                           branch_emulate_step);
 281
 282         /*
 283          * 3. load instruction to be emulated into relevant register, and
 284          */
 285         temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
 286         patch_imm64_load_insns(ppc_inst_as_u64(temp), 4, buff + TMPL_INSN_IDX);
 287
 288         /*
 289          * 4. branch back from trampoline
 290          */
 291         patch_branch((struct ppc_inst *)(buff + TMPL_RET_IDX), (unsigned long)nip, 0);
 292
 293         flush_icache_range((unsigned long)buff,
 294                            (unsigned long)(&buff[TMPL_END_IDX]));
 295
 296         op->optinsn.insn = buff;
 297
 298         return 0;
 299
 300 error:
 301         free_ppc_optinsn_slot(buff, 0);
 302         return -ERANGE;
 303
 304 }
 305
 306 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 307 {
 308         return optinsn->insn != NULL;
 309 }
 310
 311 /*
 312  * On powerpc, Optprobes always replaces one instruction (4 bytes
 313  * aligned and 4 bytes long). It is impossible to encounter another
 314  * kprobe in this address range. So always return 0.
 315  */
 316 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 317 {
 318         return 0;
 319 }
 320
 321 void arch_optimize_kprobes(struct list_head *oplist)
 322 {
 323         struct ppc_inst instr;
 324         struct optimized_kprobe *op;
 325         struct optimized_kprobe *tmp;
 326
 327         list_for_each_entry_safe(op, tmp, oplist, list) {
 328                 /*
 329                  * Backup instructions which will be replaced
 330                  * by jump address
 331                  */
 332                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 333                                                RELATIVEJUMP_SIZE);
 334                 create_branch(&instr,
 335                               (struct ppc_inst *)op->kp.addr,
 336                               (unsigned long)op->optinsn.insn, 0);
 337                 patch_instruction((struct ppc_inst *)op->kp.addr, instr);
 338                 list_del_init(&op->list);
 339         }
 340 }
 341
 342 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 343 {
 344         arch_arm_kprobe(&op->kp);
 345 }
 346
 347 void arch_unoptimize_kprobes(struct list_head *oplist,
 348                              struct list_head *done_list)
 349 {
 350         struct optimized_kprobe *op;
 351         struct optimized_kprobe *tmp;
 352
 353         list_for_each_entry_safe(op, tmp, oplist, list) {
 354                 arch_unoptimize_kprobe(op);
 355                 list_move(&op->list, done_list);
 356         }
 357 }
 358
 359 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 360                                  unsigned long addr)
 361 {
 362         return ((unsigned long)op->kp.addr <= addr &&
 363                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 364 }