arch/x86/mm/kmemcheck/opcode.c

   1 #include <linux/types.h>
   2
   3 #include "opcode.h"
   4
   5 static bool opcode_is_prefix(uint8_t b)
   6 {
   7         return
   8                 /* Group 1 */
   9                 b == 0xf0 || b == 0xf2 || b == 0xf3
  10                 /* Group 2 */
  11                 || b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26
  12                 || b == 0x64 || b == 0x65
  13                 /* Group 3 */
  14                 || b == 0x66
  15                 /* Group 4 */
  16                 || b == 0x67;
  17 }
  18
  19 #ifdef CONFIG_X86_64
  20 static bool opcode_is_rex_prefix(uint8_t b)
  21 {
  22         return (b & 0xf0) == 0x40;
  23 }
  24 #else
  25 static bool opcode_is_rex_prefix(uint8_t b)
  26 {
  27         return false;
  28 }
  29 #endif
  30
  31 #define REX_W (1 << 3)
  32
  33 /*
  34  * This is a VERY crude opcode decoder. We only need to find the size of the
  35  * load/store that caused our #PF and this should work for all the opcodes
  36  * that we care about. Moreover, the ones who invented this instruction set
  37  * should be shot.
  38  */
  39 void kmemcheck_opcode_decode(const uint8_t *op, unsigned int *size)
  40 {
  41         /* Default operand size */
  42         int operand_size_override = 4;
  43
  44         /* prefixes */
  45         for (; opcode_is_prefix(*op); ++op) {
  46                 if (*op == 0x66)
  47                         operand_size_override = 2;
  48         }
  49
  50         /* REX prefix */
  51         if (opcode_is_rex_prefix(*op)) {
  52                 uint8_t rex = *op;
  53
  54                 ++op;
  55                 if (rex & REX_W) {
  56                         switch (*op) {
  57                         case 0x63:
  58                                 *size = 4;
  59                                 return;
  60                         case 0x0f:
  61                                 ++op;
  62
  63                                 switch (*op) {
  64                                 case 0xb6:
  65                                 case 0xbe:
  66                                         *size = 1;
  67                                         return;
  68                                 case 0xb7:
  69                                 case 0xbf:
  70                                         *size = 2;
  71                                         return;
  72                                 }
  73
  74                                 break;
  75                         }
  76
  77                         *size = 8;
  78                         return;
  79                 }
  80         }
  81
  82         /* escape opcode */
  83         if (*op == 0x0f) {
  84                 ++op;
  85
  86                 /*
  87                  * This is move with zero-extend and sign-extend, respectively;
  88                  * we don't have to think about 0xb6/0xbe, because this is
  89                  * already handled in the conditional below.
  90                  */
  91                 if (*op == 0xb7 || *op == 0xbf)
  92                         operand_size_override = 2;
  93         }
  94
  95         *size = (*op & 1) ? operand_size_override : 1;
  96 }
  97
  98 const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op)
  99 {
 100         /* skip prefixes */
 101         while (opcode_is_prefix(*op))
 102                 ++op;
 103         if (opcode_is_rex_prefix(*op))
 104                 ++op;
 105         return op;
 106 }