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

DEFINITIONS

1. arch_prepared_optinsn
2. arch_check_optimized_kprobe
3. can_optimize
4. __arch_remove_optimized_kprobe
5. optimized_callback
6. NOKPROBE_SYMBOL
7. arch_optimize_kprobes
8. arch_unoptimize_kprobe
9. arch_unoptimize_kprobes
10. arch_within_optimized_kprobe
11. arch_remove_optimized_kprobe

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Kernel Probes Jump Optimization (Optprobes)
   4  *
   5  * Copyright (C) IBM Corporation, 2002, 2004
   6  * Copyright (C) Hitachi Ltd., 2012
   7  * Copyright (C) Huawei Inc., 2014
   8  */
   9 
  10 #include <linux/kprobes.h>
  11 #include <linux/jump_label.h>
  12 #include <asm/kprobes.h>
  13 #include <asm/cacheflush.h>
  14 /* for arm_gen_branch */
  15 #include <asm/insn.h>
  16 /* for patch_text */
  17 #include <asm/patch.h>
  18 
  19 #include "core.h"
  20 
  21 /*
  22  * See register_usage_flags. If the probed instruction doesn't use PC,
  23  * we can copy it into template and have it executed directly without
  24  * simulation or emulation.
  25  */
  26 #define ARM_REG_PC      15
  27 #define can_kprobe_direct_exec(m)       (!test_bit(ARM_REG_PC, &(m)))
  28 
  29 /*
  30  * NOTE: the first sub and add instruction will be modified according
  31  * to the stack cost of the instruction.
  32  */
  33 asm (
  34                         ".global optprobe_template_entry\n"
  35                         "optprobe_template_entry:\n"
  36                         ".global optprobe_template_sub_sp\n"
  37                         "optprobe_template_sub_sp:"
  38                         "       sub     sp, sp, #0xff\n"
  39                         "       stmia   sp, {r0 - r14} \n"
  40                         ".global optprobe_template_add_sp\n"
  41                         "optprobe_template_add_sp:"
  42                         "       add     r3, sp, #0xff\n"
  43                         "       str     r3, [sp, #52]\n"
  44                         "       mrs     r4, cpsr\n"
  45                         "       str     r4, [sp, #64]\n"
  46                         "       mov     r1, sp\n"
  47                         "       ldr     r0, 1f\n"
  48                         "       ldr     r2, 2f\n"
  49                         /*
  50                          * AEABI requires an 8-bytes alignment stack. If
  51                          * SP % 8 != 0 (SP % 4 == 0 should be ensured),
  52                          * alloc more bytes here.
  53                          */
  54                         "       and     r4, sp, #4\n"
  55                         "       sub     sp, sp, r4\n"
  56 #if __LINUX_ARM_ARCH__ >= 5
  57                         "       blx     r2\n"
  58 #else
  59                         "       mov     lr, pc\n"
  60                         "       mov     pc, r2\n"
  61 #endif
  62                         "       add     sp, sp, r4\n"
  63                         "       ldr     r1, [sp, #64]\n"
  64                         "       tst     r1, #"__stringify(PSR_T_BIT)"\n"
  65                         "       ldrne   r2, [sp, #60]\n"
  66                         "       orrne   r2, #1\n"
  67                         "       strne   r2, [sp, #60] @ set bit0 of PC for thumb\n"
  68                         "       msr     cpsr_cxsf, r1\n"
  69                         ".global optprobe_template_restore_begin\n"
  70                         "optprobe_template_restore_begin:\n"
  71                         "       ldmia   sp, {r0 - r15}\n"
  72                         ".global optprobe_template_restore_orig_insn\n"
  73                         "optprobe_template_restore_orig_insn:\n"
  74                         "       nop\n"
  75                         ".global optprobe_template_restore_end\n"
  76                         "optprobe_template_restore_end:\n"
  77                         "       nop\n"
  78                         ".global optprobe_template_val\n"
  79                         "optprobe_template_val:\n"
  80                         "1:     .long 0\n"
  81                         ".global optprobe_template_call\n"
  82                         "optprobe_template_call:\n"
  83                         "2:     .long 0\n"
  84                         ".global optprobe_template_end\n"
  85                         "optprobe_template_end:\n");
  86 
  87 #define TMPL_VAL_IDX \
  88         ((unsigned long *)&optprobe_template_val - (unsigned long *)&optprobe_template_entry)
  89 #define TMPL_CALL_IDX \
  90         ((unsigned long *)&optprobe_template_call - (unsigned long *)&optprobe_template_entry)
  91 #define TMPL_END_IDX \
  92         ((unsigned long *)&optprobe_template_end - (unsigned long *)&optprobe_template_entry)
  93 #define TMPL_ADD_SP \
  94         ((unsigned long *)&optprobe_template_add_sp - (unsigned long *)&optprobe_template_entry)
  95 #define TMPL_SUB_SP \
  96         ((unsigned long *)&optprobe_template_sub_sp - (unsigned long *)&optprobe_template_entry)
  97 #define TMPL_RESTORE_BEGIN \
  98         ((unsigned long *)&optprobe_template_restore_begin - (unsigned long *)&optprobe_template_entry)
  99 #define TMPL_RESTORE_ORIGN_INSN \
 100         ((unsigned long *)&optprobe_template_restore_orig_insn - (unsigned long *)&optprobe_template_entry)
 101 #define TMPL_RESTORE_END \
 102         ((unsigned long *)&optprobe_template_restore_end - (unsigned long *)&optprobe_template_entry)
 103 
 104 /*
 105  * ARM can always optimize an instruction when using ARM ISA, except
 106  * instructions like 'str r0, [sp, r1]' which store to stack and unable
 107  * to determine stack space consumption statically.
 108  */
 109 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 110 {
 111         return optinsn->insn != NULL;
 112 }
 113 
 114 /*
 115  * In ARM ISA, kprobe opt always replace one instruction (4 bytes
 116  * aligned and 4 bytes long). It is impossible to encounter another
 117  * kprobe in the address range. So always return 0.
 118  */
 119 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 120 {
 121         return 0;
 122 }
 123 
 124 /* Caller must ensure addr & 3 == 0 */
 125 static int can_optimize(struct kprobe *kp)
 126 {
 127         if (kp->ainsn.stack_space < 0)
 128                 return 0;
 129         /*
 130          * 255 is the biggest imm can be used in 'sub r0, r0, #<imm>'.
 131          * Number larger than 255 needs special encoding.
 132          */
 133         if (kp->ainsn.stack_space > 255 - sizeof(struct pt_regs))
 134                 return 0;
 135         return 1;
 136 }
 137 
 138 /* Free optimized instruction slot */
 139 static void
 140 __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 141 {
 142         if (op->optinsn.insn) {
 143                 free_optinsn_slot(op->optinsn.insn, dirty);
 144                 op->optinsn.insn = NULL;
 145         }
 146 }
 147 
 148 extern void kprobe_handler(struct pt_regs *regs);
 149 
 150 static void
 151 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 152 {
 153         unsigned long flags;
 154         struct kprobe *p = &op->kp;
 155         struct kprobe_ctlblk *kcb;
 156 
 157         /* Save skipped registers */
 158         regs->ARM_pc = (unsigned long)op->kp.addr;
 159         regs->ARM_ORIG_r0 = ~0UL;
 160 
 161         local_irq_save(flags);
 162         kcb = get_kprobe_ctlblk();
 163 
 164         if (kprobe_running()) {
 165                 kprobes_inc_nmissed_count(&op->kp);
 166         } else {
 167                 __this_cpu_write(current_kprobe, &op->kp);
 168                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 169                 opt_pre_handler(&op->kp, regs);
 170                 __this_cpu_write(current_kprobe, NULL);
 171         }
 172 
 173         /*
 174          * We singlestep the replaced instruction only when it can't be
 175          * executed directly during restore.
 176          */
 177         if (!p->ainsn.kprobe_direct_exec)
 178                 op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
 179 
 180         local_irq_restore(flags);
 181 }
 182 NOKPROBE_SYMBOL(optimized_callback)
 183 
 184 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
 185 {
 186         kprobe_opcode_t *code;
 187         unsigned long rel_chk;
 188         unsigned long val;
 189         unsigned long stack_protect = sizeof(struct pt_regs);
 190 
 191         if (!can_optimize(orig))
 192                 return -EILSEQ;
 193 
 194         code = get_optinsn_slot();
 195         if (!code)
 196                 return -ENOMEM;
 197 
 198         /*
 199          * Verify if the address gap is in 32MiB range, because this uses
 200          * a relative jump.
 201          *
 202          * kprobe opt use a 'b' instruction to branch to optinsn.insn.
 203          * According to ARM manual, branch instruction is:
 204          *
 205          *   31  28 27           24 23             0
 206          *  +------+---+---+---+---+----------------+
 207          *  | cond | 1 | 0 | 1 | 0 |      imm24     |
 208          *  +------+---+---+---+---+----------------+
 209          *
 210          * imm24 is a signed 24 bits integer. The real branch offset is computed
 211          * by: imm32 = SignExtend(imm24:'00', 32);
 212          *
 213          * So the maximum forward branch should be:
 214          *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
 215          * The maximum backword branch should be:
 216          *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
 217          *
 218          * We can simply check (rel & 0xfe000003):
 219          *  if rel is positive, (rel & 0xfe000000) shoule be 0
 220          *  if rel is negitive, (rel & 0xfe000000) should be 0xfe000000
 221          *  the last '3' is used for alignment checking.
 222          */
 223         rel_chk = (unsigned long)((long)code -
 224                         (long)orig->addr + 8) & 0xfe000003;
 225 
 226         if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
 227                 /*
 228                  * Different from x86, we free code buf directly instead of
 229                  * calling __arch_remove_optimized_kprobe() because
 230                  * we have not fill any field in op.
 231                  */
 232                 free_optinsn_slot(code, 0);
 233                 return -ERANGE;
 234         }
 235 
 236         /* Copy arch-dep-instance from template. */
 237         memcpy(code, (unsigned long *)&optprobe_template_entry,
 238                         TMPL_END_IDX * sizeof(kprobe_opcode_t));
 239 
 240         /* Adjust buffer according to instruction. */
 241         BUG_ON(orig->ainsn.stack_space < 0);
 242 
 243         stack_protect += orig->ainsn.stack_space;
 244 
 245         /* Should have been filtered by can_optimize(). */
 246         BUG_ON(stack_protect > 255);
 247 
 248         /* Create a 'sub sp, sp, #<stack_protect>' */
 249         code[TMPL_SUB_SP] = __opcode_to_mem_arm(0xe24dd000 | stack_protect);
 250         /* Create a 'add r3, sp, #<stack_protect>' */
 251         code[TMPL_ADD_SP] = __opcode_to_mem_arm(0xe28d3000 | stack_protect);
 252 
 253         /* Set probe information */
 254         val = (unsigned long)op;
 255         code[TMPL_VAL_IDX] = val;
 256 
 257         /* Set probe function call */
 258         val = (unsigned long)optimized_callback;
 259         code[TMPL_CALL_IDX] = val;
 260 
 261         /* If possible, copy insn and have it executed during restore */
 262         orig->ainsn.kprobe_direct_exec = false;
 263         if (can_kprobe_direct_exec(orig->ainsn.register_usage_flags)) {
 264                 kprobe_opcode_t final_branch = arm_gen_branch(
 265                                 (unsigned long)(&code[TMPL_RESTORE_END]),
 266                                 (unsigned long)(op->kp.addr) + 4);
 267                 if (final_branch != 0) {
 268                         /*
 269                          * Replace original 'ldmia sp, {r0 - r15}' with
 270                          * 'ldmia {r0 - r14}', restore all registers except pc.
 271                          */
 272                         code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);
 273 
 274                         /* The original probed instruction */
 275                         code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);
 276 
 277                         /* Jump back to next instruction */
 278                         code[TMPL_RESTORE_END] = __opcode_to_mem_arm(final_branch);
 279                         orig->ainsn.kprobe_direct_exec = true;
 280                 }
 281         }
 282 
 283         flush_icache_range((unsigned long)code,
 284                            (unsigned long)(&code[TMPL_END_IDX]));
 285 
 286         /* Set op->optinsn.insn means prepared. */
 287         op->optinsn.insn = code;
 288         return 0;
 289 }
 290 
 291 void __kprobes arch_optimize_kprobes(struct list_head *oplist)
 292 {
 293         struct optimized_kprobe *op, *tmp;
 294 
 295         list_for_each_entry_safe(op, tmp, oplist, list) {
 296                 unsigned long insn;
 297                 WARN_ON(kprobe_disabled(&op->kp));
 298 
 299                 /*
 300                  * Backup instructions which will be replaced
 301                  * by jump address
 302                  */
 303                 memcpy(op->optinsn.copied_insn, op->kp.addr,
 304                                 RELATIVEJUMP_SIZE);
 305 
 306                 insn = arm_gen_branch((unsigned long)op->kp.addr,
 307                                 (unsigned long)op->optinsn.insn);
 308                 BUG_ON(insn == 0);
 309 
 310                 /*
 311                  * Make it a conditional branch if replaced insn
 312                  * is consitional
 313                  */
 314                 insn = (__mem_to_opcode_arm(
 315                           op->optinsn.copied_insn[0]) & 0xf0000000) |
 316                         (insn & 0x0fffffff);
 317 
 318                 /*
 319                  * Similar to __arch_disarm_kprobe, operations which
 320                  * removing breakpoints must be wrapped by stop_machine
 321                  * to avoid racing.
 322                  */
 323                 kprobes_remove_breakpoint(op->kp.addr, insn);
 324 
 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 /*
 335  * Recover original instructions and breakpoints from relative jumps.
 336  * Caller must call with locking kprobe_mutex.
 337  */
 338 void arch_unoptimize_kprobes(struct list_head *oplist,
 339                             struct list_head *done_list)
 340 {
 341         struct optimized_kprobe *op, *tmp;
 342 
 343         list_for_each_entry_safe(op, tmp, oplist, list) {
 344                 arch_unoptimize_kprobe(op);
 345                 list_move(&op->list, done_list);
 346         }
 347 }
 348 
 349 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 350                                 unsigned long addr)
 351 {
 352         return ((unsigned long)op->kp.addr <= addr &&
 353                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 354 }
 355 
 356 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 357 {
 358         __arch_remove_optimized_kprobe(op, 1);
 359 }