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
  20 #define TMPL_CALL_HDLR_IDX      \
  21         (optprobe_template_call_handler - optprobe_template_entry)
  22 #define TMPL_EMULATE_IDX        \
  23         (optprobe_template_call_emulate - optprobe_template_entry)
  24 #define TMPL_RET_IDX            \
  25         (optprobe_template_ret - optprobe_template_entry)
  26 #define TMPL_OP_IDX             \
  27         (optprobe_template_op_address - optprobe_template_entry)
  28 #define TMPL_INSN_IDX           \
  29         (optprobe_template_insn - optprobe_template_entry)
  30 #define TMPL_END_IDX            \
  31         (optprobe_template_end - optprobe_template_entry)
  32
  33 DEFINE_INSN_CACHE_OPS(ppc_optinsn);
  34
  35 static bool insn_page_in_use;
  36
  37 static void *__ppc_alloc_insn_page(void)
  38 {
  39         if (insn_page_in_use)
  40                 return NULL;
  41         insn_page_in_use = true;
  42         return &optinsn_slot;
  43 }
  44
  45 static void __ppc_free_insn_page(void *page __maybe_unused)
  46 {
  47         insn_page_in_use = false;
  48 }
  49
  50 struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
  51         .mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
  52         .pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
  53         /* insn_size initialized later */
  54         .alloc = __ppc_alloc_insn_page,
  55         .free = __ppc_free_insn_page,
  56         .nr_garbage = 0,
  57 };
  58
  59 /*
  60  * Check if we can optimize this probe. Returns NIP post-emulation if this can
  61  * be optimized and 0 otherwise.
  62  */
  63 static unsigned long can_optimize(struct kprobe *p)
  64 {
  65         struct pt_regs regs;
  66         struct instruction_op op;
  67         unsigned long nip = 0;
  68
  69         /*
  70          * kprobe placed for kretprobe during boot time
  71          * has a 'nop' instruction, which can be emulated.
  72          * So further checks can be skipped.
  73          */
  74         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
  75                 return (unsigned long)p->addr + sizeof(kprobe_opcode_t);
  76
  77         /*
  78          * We only support optimizing kernel addresses, but not
  79          * module addresses.
  80          *
  81          * FIXME: Optimize kprobes placed in module addresses.
  82          */
  83         if (!is_kernel_addr((unsigned long)p->addr))
  84                 return 0;
  85
  86         memset(&regs, 0, sizeof(struct pt_regs));
  87         regs.nip = (unsigned long)p->addr;
  88         regs.trap = 0x0;
  89         regs.msr = MSR_KERNEL;
  90
  91         /*
  92          * Kprobe placed in conditional branch instructions are
  93          * not optimized, as we can't predict the nip prior with
  94          * dummy pt_regs and can not ensure that the return branch
  95          * from detour buffer falls in the range of address (i.e 32MB).
  96          * A branch back from trampoline is set up in the detour buffer
  97          * to the nip returned by the analyse_instr() here.
  98          *
  99          * Ensure that the instruction is not a conditional branch,
 100          * and that can be emulated.
 101          */
 102         if (!is_conditional_branch(*p->ainsn.insn) &&
 103                         analyse_instr(&op, &regs, *p->ainsn.insn) == 1) {
 104                 emulate_update_regs(&regs, &op);
 105                 nip = regs.nip;
 106         }
 107
 108         return nip;
 109 }
 110
 111 static void optimized_callback(struct optimized_kprobe *op,
 112                                struct pt_regs *regs)
 113 {
 114         /* This is possible if op is under delayed unoptimizing */
 115         if (kprobe_disabled(&op->kp))
 116                 return;
 117
 118         preempt_disable();
 119
 120         if (kprobe_running()) {
 121                 kprobes_inc_nmissed_count(&op->kp);
 122         } else {
 123                 __this_cpu_write(current_kprobe, &op->kp);
 124                 regs->nip = (unsigned long)op->kp.addr;
 125                 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 126                 opt_pre_handler(&op->kp, regs);
 127                 __this_cpu_write(current_kprobe, NULL);
 128         }
 129
 130         preempt_enable_no_resched();
 131 }
 132 NOKPROBE_SYMBOL(optimized_callback);
 133
 134 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 135 {
 136         if (op->optinsn.insn) {
 137                 free_ppc_optinsn_slot(op->optinsn.insn, 1);
 138                 op->optinsn.insn = NULL;
 139         }
 140 }
 141
 142 /*
 143  * emulate_step() requires insn to be emulated as
 144  * second parameter. Load register 'r4' with the
 145  * instruction.
 146  */
 147 void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
 148 {
 149         /* addis r4,0,(insn)@h */
 150         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(4) |
 151                           ((val >> 16) & 0xffff));
 152         addr++;
 153
 154         /* ori r4,r4,(insn)@l */
 155         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(4) |
 156                           ___PPC_RS(4) | (val & 0xffff));
 157 }
 158
 159 /*
 160  * Generate instructions to load provided immediate 64-bit value
 161  * to register 'r3' and patch these instructions at 'addr'.
 162  */
 163 void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
 164 {
 165         /* lis r3,(op)@highest */
 166         patch_instruction(addr, PPC_INST_ADDIS | ___PPC_RT(3) |
 167                           ((val >> 48) & 0xffff));
 168         addr++;
 169
 170         /* ori r3,r3,(op)@higher */
 171         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 172                           ___PPC_RS(3) | ((val >> 32) & 0xffff));
 173         addr++;
 174
 175         /* rldicr r3,r3,32,31 */
 176         patch_instruction(addr, PPC_INST_RLDICR | ___PPC_RA(3) |
 177                           ___PPC_RS(3) | __PPC_SH64(32) | __PPC_ME64(31));
 178         addr++;
 179
 180         /* oris r3,r3,(op)@h */
 181         patch_instruction(addr, PPC_INST_ORIS | ___PPC_RA(3) |
 182                           ___PPC_RS(3) | ((val >> 16) & 0xffff));
 183         addr++;
 184
 185         /* ori r3,r3,(op)@l */
 186         patch_instruction(addr, PPC_INST_ORI | ___PPC_RA(3) |
 187                           ___PPC_RS(3) | (val & 0xffff));
 188 }
 189
 190 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 191 {
 192         kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
 193         kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
 194         long b_offset;
 195         unsigned long nip, size;
 196         int rc, i;
 197
 198         kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 199
 200         nip = can_optimize(p);
 201         if (!nip)
 202                 return -EILSEQ;
 203
 204         /* Allocate instruction slot for detour buffer */
 205         buff = get_ppc_optinsn_slot();
 206         if (!buff)
 207                 return -ENOMEM;
 208
 209         /*
 210          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 211          *
 212          * The target address has to be relatively nearby, to permit use
 213          * of branch instruction in powerpc, because the address is specified
 214          * in an immediate field in the instruction opcode itself, ie 24 bits
 215          * in the opcode specify the address. Therefore the address should
 216          * be within 32MB on either side of the current instruction.
 217          */
 218         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 219         if (!is_offset_in_branch_range(b_offset))
 220                 goto error;
 221
 222         /* Check if the return address is also within 32MB range */
 223         b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
 224                         (unsigned long)nip;
 225         if (!is_offset_in_branch_range(b_offset))
 226                 goto error;
 227
 228         /* Setup template */
 229         /* We can optimize this via patch_instruction_window later */
 230         size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
 231         pr_devel("Copying template to %p, size %lu\n", buff, size);
 232         for (i = 0; i < size; i++) {
 233                 rc = patch_instruction(buff + i, *(optprobe_template_entry + i));
 234                 if (rc < 0)
 235                         goto error;
 236         }
 237
 238         /*
 239          * Fixup the template with instructions to:
 240          * 1. load the address of the actual probepoint
 241          */
 242         patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
 243
 244         /*
 245          * 2. branch to optimized_callback() and emulate_step()
 246          */
 247         op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
 248         emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
 249         if (!op_callback_addr || !emulate_step_addr) {
 250                 WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 251                 goto error;
 252         }
 253
 254         branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
 255                                 (unsigned long)op_callback_addr,
 256                                 BRANCH_SET_LINK);
 257
 258         branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
 259                                 (unsigned long)emulate_step_addr,
 260                                 BRANCH_SET_LINK);
 261
 262         if (!branch_op_callback || !branch_emulate_step)
 263                 goto error;
 264
 265         patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
 266         patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);
 267
 268         /*
 269          * 3. load instruction to be emulated into relevant register, and
 270          */
 271         patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
 272
 273         /*
 274          * 4. branch back from trampoline
 275          */
 276         patch_branch(buff + TMPL_RET_IDX, (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 }