git.zerfleddert.de Git - rsbs2/blob - rsb-crc.c

   1 #include <stdio.h>
   2
   3 #define POLY 0x04c11db7
   4
   5 /* Theory of operation:
   6  * (arm-elf-objdump -b binary -m arm -M reg-names-raw -D RSB_S2_SINGLE.bin)
   7  * Addresses: 0x4c4, 0x55ae0, 0x59734
   8  *
   9  * 440: push  {r4, r5, r6, r7, r8, r9, r10, r11, r14}
  10  * 444: mov   r11, r0
  11  * 448: mov   r10, r1
  12  * 44c: mov   r14, r2
  13  * 450: mov   r6, #0    ; 0x0
  14  * 454: b     0x4a0
  15  * 458: add   r3, r6, r10
  16  * 45c: ldrb  r3, [r3]
  17  * 460: lsl   r3, r3, #24
  18  * 464: eor   r11, r11, r3
  19  * 468: mov   r5, #8    ; 0x8
  20  * 46c: and   r3, r11, #-2147483648     ; 0x80000000
  21  * 470: cmp   r3, #0    ; 0x0
  22  * 474: beq   0x48c
  23  * 478: lsl   r3, r11, #1
  24  * 47c: ldr   r12, [pc, #64]    ; 0x4c4
  25  * 480: eor   r0, r3, r12
  26  * 484: mov   r11, r0
  27  * 488: b     0x490
  28  * 48c: lsl   r11, r11, #1
  29  * 490: sub   r5, r5, #1        ; 0x1
  30  * 494: cmp   r5, #0            ; 0x0
  31  * 498: bne   0x46c
  32  * 49c: add   r6, r6, #1        ; 0x1
  33  * 4a0: cmp   r6, r14
  34  * 4a4: blt   0x458
  35  * 4a8: mov   r0, r11
  36  * 4ac: pop   {r4, r5, r6, r7, r8, r9, r10, r11, r15}
  37  * 4c4: DATA: 0x04c11db7
  38  */
  39
  40 unsigned int rsb_crc(unsigned int r11_crc, unsigned char *r10_buf, unsigned int r14_len) {
  41         unsigned int r6_pos = 0;
  42         unsigned int r3_data;
  43         int r5_bit;
  44
  45         while (r6_pos < r14_len) {
  46                 r3_data = (*(r6_pos+r10_buf)) << 24;
  47                 r11_crc = r11_crc ^ r3_data;
  48
  49                 r5_bit = 8;
  50
  51                 do {
  52                         r3_data = r11_crc & 0x80000000;
  53
  54                         if (r3_data != 0) {
  55                                 r3_data = r11_crc << 1;
  56                                 r11_crc = r3_data ^ POLY;
  57                         } else {
  58                                 r11_crc = r11_crc << 1;
  59                         }
  60                         r5_bit--;
  61                 } while (r5_bit);
  62
  63                 r6_pos++;
  64         }
  65
  66         return r11_crc;
  67 }
  68
  69 /* Second broken algorithm:
  70  *
  71  * 55a30: push    {r3, r4, r5, r6, r7, r8, r9, r14}
  72  * 55a34: bl      0x55a3c
  73  * 55a38: pop     {r3, r4, r5, r6, r7, r8, r9, r15}
  74  * 55a3c: mov     r8, #1  ; 0x1
  75  * 55a40: mov     r3, #-1073741824        ; 0xc0000000
  76  * 55a44: cmp     r0, r3
  77  * 55a48: ble     0x55ad8
  78  * 55a4c: mov     r3, #32 ; 0x20
  79  * 55a50: ldr     r4, [r3, r0]!
  80  * 55a54: mov     r8, #2  ; 0x2
  81  * 55a58: ldr     r5, [r3, #4]
  82  * 55a5c: cmp     r5, r2
  83  * 55a60: bne     0x55ad8
  84  * 55a64: mov     r8, #3  ; 0x3
  85  * 55a68: cmp     r1, r4
  86  * 55a6c: movscs  r5, #0  ; 0x0
  87  * 55a70: movscc  r5, #1  ; 0x1
  88  * 55a74: bne     0x55ad8
  89  * 55a78: mov     r8, #4  ; 0x4
  90  * 55a7c: mov     r3, r0
  91  * 55a80: add     r4, r0, r4
  92  * 55a84: mvn     r5, #0  ; 0x0
  93  * 55a88: ldr     r7, [pc, #80]   ; 0x55ae0
  94  * 55a8c: cmp     r3, r4
  95  * 55a90: bcs     0x55ac8
  96  * 55a94: bic     r9, r3, #3      ; 0x3
  97  * 55a98: ldr     r6, [r9]
  98  * 55a9c: and     r9, r3, #3      ; 0x3
  99  * 55aa0: lsl     r9, r9, #3
 100  * 55aa4: lsr     r6, r6, r9
 101  * 55aa8: eor     r5, r5, r6, lsl #24
 102  * 55aac: mov     r6, #8  ; 0x8
 103  * 55ab0: lsls    r5, r5, #1
 104  * 55ab4: eorcs   r5, r5, r7
 105  * 55ab8: subs    r6, r6, #1      ; 0x1
 106  * 55abc: bne     0x55ab0
 107  * 55ac0: add     r3, r3, #1      ; 0x1
 108  * 55ac4: b       0x55a8c
 109  * 55ac8: mvn     r5, r5
 110  * 55acc: ldr     r3, [r4]
 111  * 55ad0: subs    r3, r3, r5
 112  * 55ad4: moveq   r8, #0  ; 0x0
 113  * 55ad8: mov     r0, r8
 114  * 55adc: mov     r15, r14
 115  * 55ae0: DATA:   0x04c11db7
 116  */
 117
 118 unsigned int rsb_crc2(unsigned char *r0_buf, unsigned int r1_buflen, unsigned int r2_magic, unsigned int *crc_out) {
 119         unsigned int r4_len;
 120         unsigned int file_crc;
 121
 122         r4_len = *(unsigned int*)(r0_buf + 0x20);
 123
 124         if (*((unsigned int*)(r0_buf + 0x24)) != r2_magic)
 125                 return 2; /* MAGIC does not match */
 126
 127         if (r1_buflen < r4_len)
 128                 return 3; /* image to small */
 129
 130         *crc_out = ~rsb_crc(~0x0, r0_buf, r4_len);
 131
 132         file_crc = *((unsigned int*)(r0_buf + r4_len));
 133
 134         if (file_crc != *crc_out)
 135                 return 4;
 136
 137         return 0;
 138 }