arch/arm/probes/kprobes/opt-arm.c

   1 /*
   2  *  Kernel Probes Jump Optimization (Optprobes)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2002, 2004
  19  * Copyright (C) Hitachi Ltd., 2012
  20  * Copyright (C) Huawei Inc., 2014
  21  */
  22
  23 #include <linux/kprobes.h>
  24 #include <linux/jump_label.h>
  25 #include <asm/kprobes.h>
  26 #include <asm/cacheflush.h>
  27 /* for arm_gen_branch */
  28 #include <asm/insn.h>
  29 /* for patch_text */
  30 #include <asm/patch.h>
  31
  32 #include "core.h"
  33
  34 /*
  35  * See register_usage_flags. If the probed instruction doesn't use PC,
  36  * we can copy it into template and have it executed directly without
  37  * simulation or emulation.
  38  */
  39 #define ARM_REG_PC      15
  40 #define can_kprobe_direct_exec(m)       (!test_bit(ARM_REG_PC, &(m)))
  41
  42 /*
  43  * NOTE: the first sub and add instruction will be modified according
  44  * to the stack cost of the instruction.
  45  */
  46 asm (
  47                         ".global optprobe_template_entry\n"
  48                         "optprobe_template_entry:\n"
  49                         ".global optprobe_template_sub_sp\n"
  50                         "optprobe_template_sub_sp:"
  51                         "       sub     sp, sp, #0xff\n"
  52                         "       stmia   sp, {r0 - r14} \n"
  53                         ".global optprobe_template_add_sp\n"
  54                         "optprobe_template_add_sp:"
  55                         "       add     r3, sp, #0xff\n"
  56                         "       str     r3, [sp, #52]\n"
  57                         "       mrs     r4, cpsr\n"
  58                         "       str     r4, [sp, #64]\n"
  59                         "       mov     r1, sp\n"
  60                         "       ldr     r0, 1f\n"
  61                         "       ldr     r2, 2f\n"
  62                         /*
  63                          * AEABI requires an 8-bytes alignment stack. If
  64                          * SP % 8 != 0 (SP % 4 == 0 should be ensured),
  65                          * alloc more bytes here.
  66                          */
  67                         "       and     r4, sp, #4\n"
  68                         "       sub     sp, sp, r4\n"
  69 #if __LINUX_ARM_ARCH__ >= 5
  70                         "       blx     r2\n"
  71 #else
  72                         "       mov     lr, pc\n"
  73                         "       mov     pc, r2\n"
  74 #endif
  75                         "       add     sp, sp, r4\n"
  76                         "       ldr     r1, [sp, #64]\n"
  77                         "       tst     r1, #"__stringify(PSR_T_BIT)"\n"
  78                         "       ldrne   r2, [sp, #60]\n"
  79                         "       orrne   r2, #1\n"
  80                         "       strne   r2, [sp, #60] @ set bit0 of PC for thumb\n"
  81                         "       msr     cpsr_cxsf, r1\n"
  82                         ".global optprobe_template_restore_begin\n"
  83                         "optprobe_template_restore_begin:\n"
  84                         "       ldmia   sp, {r0 - r15}\n"
  85                         ".global optprobe_template_restore_orig_insn\n"
  86                         "optprobe_template_restore_orig_insn:\n"
  87                         "       nop\n"
  88                         ".global optprobe_template_restore_end\n"
  89                         "optprobe_template_restore_end:\n"
  90                         "       nop\n"
  91                         ".global optprobe_template_val\n"
  92                         "optprobe_template_val:\n"
  93                         "1:     .long 0\n"
  94                         ".global optprobe_template_call\n"
  95                         "optprobe_template_call:\n"
  96                         "2:     .long 0\n"
  97                         ".global optprobe_template_end\n"
  98                         "optprobe_template_end:\n");
  99
 100 #define TMPL_VAL_IDX \
 101         ((unsigned long *)&optprobe_template_val - (unsigned long *)&optprobe_template_entry)
 102 #define TMPL_CALL_IDX \
 103         ((unsigned long *)&optprobe_template_call - (unsigned long *)&optprobe_template_entry)
 104 #define TMPL_END_IDX \
 105         ((unsigned long *)&optprobe_template_end - (unsigned long *)&optprobe_template_entry)
 106 #define TMPL_ADD_SP \
 107         ((unsigned long *)&optprobe_template_add_sp - (unsigned long *)&optprobe_template_entry)
 108 #define TMPL_SUB_SP \
 109         ((unsigned long *)&optprobe_template_sub_sp - (unsigned long *)&optprobe_template_entry)
 110 #define TMPL_RESTORE_BEGIN \
 111         ((unsigned long *)&optprobe_template_restore_begin - (unsigned long *)&optprobe_template_entry)
 112 #define TMPL_RESTORE_ORIGN_INSN \
 113         ((unsigned long *)&optprobe_template_restore_orig_insn - (unsigned long *)&optprobe_template_entry)
 114 #define TMPL_RESTORE_END \
 115         ((unsigned long *)&optprobe_template_restore_end - (unsigned long *)&optprobe_template_entry)
 116
 117 /*
 118  * ARM can always optimize an instruction when using ARM ISA, except
 119  * instructions like 'str r0, [sp, r1]' which store to stack and unable
 120  * to determine stack space consumption statically.
 121  */
 122 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 123 {
 124         return optinsn->insn != NULL;
 125 }
 126
 127 /*
 128  * In ARM ISA, kprobe opt always replace one instruction (4 bytes
 129  * aligned and 4 bytes long). It is impossible to encounter another
 130  * kprobe in the address range. So always return 0.
 131  */
 132 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 133 {
 134         return 0;
 135 }
 136
 137 /* Caller must ensure addr & 3 == 0 */
 138 static int can_optimize(struct kprobe *kp)
 139 {
 140         if (kp->ainsn.stack_space < 0)
 141                 return 0;
 142         /*
 143          * 255 is the biggest imm can be used in 'sub r0, r0, #<imm>'.
 144          * Number larger than 255 needs special encoding.
 145          */
 146         if (kp->ainsn.stack_space > 255 - sizeof(struct pt_regs))
 147                 return 0;
 148         return 1;
 149 }
 150
 151 /* Free optimized instruction slot */
 152 static void
 153 __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 154 {
 155         if (op->optinsn.insn) {
 156                 free_optinsn_slot(op->optinsn.insn, dirty);
 157                 op->optinsn.insn = NULL;
 158         }
 159 }
 160
 161 extern void kprobe_handler(struct pt_regs *regs);
 162
 163 static void
 164 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 165 {
 166         unsigned long flags;
 167         struct kprobe *p = &op->kp;
 168         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 169
 170         /* Save skipped registers */
 171         regs->ARM_pc = (unsigned long)op->kp.addr;
 172         regs->ARM_ORIG_r0 = ~0UL;
 173
 174         local_irq_save(flags);
 175
 176         if (kprobe_running()) {
 177                 kprobes_inc_nmissed_count(&op->kp);
 178         } else {
 179                 __this_cpu_write(current_kprobe, &op->kp);
 180                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 181                 opt_pre_handler(&op->kp, regs);
 182                 __this_cpu_write(current_kprobe, NULL);
 183         }
 184
 185         /*
 186          * We singlestep the replaced instruction only when it can't be
 187          * executed directly during restore.
 188          */
 189         if (!p->ainsn.kprobe_direct_exec)
 190                 op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
 191
 192         local_irq_restore(flags);
 193 }
 194
 195 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
 196 {
 197         kprobe_opcode_t *code;
 198         unsigned long rel_chk;
 199         unsigned long val;
 200         unsigned long stack_protect = sizeof(struct pt_regs);
 201
 202         if (!can_optimize(orig))
 203                 return -EILSEQ;
 204
 205         code = get_optinsn_slot();
 206         if (!code)
 207                 return -ENOMEM;
 208
 209         /*
 210          * Verify if the address gap is in 32MiB range, because this uses
 211          * a relative jump.
 212          *
 213          * kprobe opt use a 'b' instruction to branch to optinsn.insn.
 214          * According to ARM manual, branch instruction is:
 215          *
 216          *   31  28 27           24 23             0
 217          *  +------+---+---+---+---+----------------+
 218          *  | cond | 1 | 0 | 1 | 0 |      imm24     |
 219          *  +------+---+---+---+---+----------------+
 220          *
 221          * imm24 is a signed 24 bits integer. The real branch offset is computed
 222          * by: imm32 = SignExtend(imm24:'00', 32);
 223          *
 224          * So the maximum forward branch should be:
 225          *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
 226          * The maximum backword branch should be:
 227          *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
 228          *
 229          * We can simply check (rel & 0xfe000003):
 230          *  if rel is positive, (rel & 0xfe000000) shoule be 0
 231          *  if rel is negitive, (rel & 0xfe000000) should be 0xfe000000
 232          *  the last '3' is used for alignment checking.
 233          */
 234         rel_chk = (unsigned long)((long)code -
 235                         (long)orig->addr + 8) & 0xfe000003;
 236
 237         if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
 238                 /*
 239                  * Different from x86, we free code buf directly instead of
 240                  * calling __arch_remove_optimized_kprobe() because
 241                  * we have not fill any field in op.
 242                  */
 243                 free_optinsn_slot(code, 0);
 244                 return -ERANGE;
 245         }
 246
 247         /* Copy arch-dep-instance from template. */
 248         memcpy(code, &optprobe_template_entry,
 249                         TMPL_END_IDX * sizeof(kprobe_opcode_t));
 250
 251         /* Adjust buffer according to instruction. */
 252         BUG_ON(orig->ainsn.stack_space < 0);
 253
 254         stack_protect += orig->ainsn.stack_space;
 255
 256         /* Should have been filtered by can_optimize(). */
 257         BUG_ON(stack_protect > 255);
 258
 259         /* Create a 'sub sp, sp, #<stack_protect>' */
 260         code[TMPL_SUB_SP] = __opcode_to_mem_arm(0xe24dd000 | stack_protect);
 261         /* Create a 'add r3, sp, #<stack_protect>' */
 262         code[TMPL_ADD_SP] = __opcode_to_mem_arm(0xe28d3000 | stack_protect);
 263
 264         /* Set probe information */
 265         val = (unsigned long)op;
 266         code[TMPL_VAL_IDX] = val;
 267
 268         /* Set probe function call */
 269         val = (unsigned long)optimized_callback;
 270         code[TMPL_CALL_IDX] = val;
 271
 272         /* If possible, copy insn and have it executed during restore */
 273         orig->ainsn.kprobe_direct_exec = false;
 274         if (can_kprobe_direct_exec(orig->ainsn.register_usage_flags)) {
 275                 kprobe_opcode_t final_branch = arm_gen_branch(
 276                                 (unsigned long)(&code[TMPL_RESTORE_END]),
 277                                 (unsigned long)(op->kp.addr) + 4);
 278                 if (final_branch != 0) {
 279                         /*
 280                          * Replace original 'ldmia sp, {r0 - r15}' with
 281                          * 'ldmia {r0 - r14}', restore all registers except pc.
 282                          */
 283                         code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);
 284
 285                         /* The original probed instruction */
 286                         code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);
 287
 288                         /* Jump back to next instruction */
 289                         code[TMPL_RESTORE_END] = __opcode_to_mem_arm(final_branch);
 290                         orig->ainsn.kprobe_direct_exec = true;
 291                 }
 292         }
 293
 294         flush_icache_range((unsigned long)code,
 295                            (unsigned long)(&code[TMPL_END_IDX]));
 296
 297         /* Set op->optinsn.insn means prepared. */
 298         op->optinsn.insn = code;
 299         return 0;
 300 }
 301
 302 void __kprobes arch_optimize_kprobes(struct list_head *oplist)
 303 {
 304         struct optimized_kprobe *op, *tmp;
 305
 306         list_for_each_entry_safe(op, tmp, oplist, list) {
 307                 unsigned long insn;
 308                 WARN_ON(kprobe_disabled(&op->kp));
 309
 310                 /*
 311                  * Backup instructions which will be replaced
 312                  * by jump address
 313                  */
 314                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 315                                 RELATIVEJUMP_SIZE);
 316
 317                 insn = arm_gen_branch((unsigned long)op->kp.addr,
 318                                 (unsigned long)op->optinsn.insn);
 319                 BUG_ON(insn == 0);
 320
 321                 /*
 322                  * Make it a conditional branch if replaced insn
 323                  * is consitional
 324                  */
 325                 insn = (__mem_to_opcode_arm(
 326                           op->optinsn.copied_insn[0]) & 0xf0000000) |
 327                         (insn & 0x0fffffff);
 328
 329                 /*
 330                  * Similar to __arch_disarm_kprobe, operations which
 331                  * removing breakpoints must be wrapped by stop_machine
 332                  * to avoid racing.
 333                  */
 334                 kprobes_remove_breakpoint(op->kp.addr, insn);
 335
 336                 list_del_init(&op->list);
 337         }
 338 }
 339
 340 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 341 {
 342         arch_arm_kprobe(&op->kp);
 343 }
 344
 345 /*
 346  * Recover original instructions and breakpoints from relative jumps.
 347  * Caller must call with locking kprobe_mutex.
 348  */
 349 void arch_unoptimize_kprobes(struct list_head *oplist,
 350                             struct list_head *done_list)
 351 {
 352         struct optimized_kprobe *op, *tmp;
 353
 354         list_for_each_entry_safe(op, tmp, oplist, list) {
 355                 arch_unoptimize_kprobe(op);
 356                 list_move(&op->list, done_list);
 357         }
 358 }
 359
 360 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 361                                 unsigned long addr)
 362 {
 363         return ((unsigned long)op->kp.addr <= addr &&
 364                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 365 }
 366
 367 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 368 {
 369         __arch_remove_optimized_kprobe(op, 1);
 370 }