blob_loader.c

#include <sys/mman.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <stdint.h>

typedef uint8_t  u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;
typedef int8_t   s8;
typedef int16_t  s16;
typedef int32_t  s32;
typedef int64_t  s64;

typedef u8* ptr;

ptr start_addr;
ptr end_addr;

void load_err(char* msg) {

  fprintf(stderr, "LOADER ERROR: %s\n", msg);
  abort();

}

u8 load_blob(ptr addr, s32 fd) {

  struct stat st;
  fstat(fd, &st);
  s32 size = st.st_size;

  addr = mmap(addr, size, PROT_READ | PROT_WRITE | PROT_EXEC,
              MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (addr == MAP_FAILED)
    return 1;

  read(fd, addr, size);

  start_addr = addr;
  end_addr = addr + size;
  
  return 0;

}

u8 load_memory_blob(ptr addr, ptr blob, s32 size) {

  addr = mmap(addr, size, PROT_READ | PROT_WRITE | PROT_EXEC,
              MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (addr == MAP_FAILED)
    return 1;

  memcpy(addr, blob, size);
  start_addr = addr;
  end_addr = addr + size;
  
  return 0;

}

u8 load_memory_blob_inplace(ptr addr, s32 size) {

  ptr align = (ptr)((unsigned long)addr &~ (sysconf(_SC_PAGESIZE) -1));
  s32 align_size = size + (addr - align);

  if (mprotect(align, align_size, PROT_READ | PROT_WRITE | PROT_EXEC) == -1)
    return 1;
  
  start_addr = addr;
  end_addr = addr + size;
  
  return 0;

}


#ifdef __x86_64__
ptr hook_place_jump(ptr addr, ptr dest_cb) {

  size_t instr_len = 5;
  u32 displ = dest_cb - (addr + instr_len);

  addr[0] = 0xe9; // relative near jmp
  *(u32*)&addr[1] = displ;

  return addr + instr_len;

}
#elif __i386__
ptr hook_place_jump(ptr addr, ptr dest_cb) {

  size_t instr_len = 5;
  u32 displ = dest_cb - (addr + instr_len);

  addr[0] = 0xe9; // relative near jmp
  *(u32*)&addr[1] = displ;
  
  return addr + instr_len;

}
#elif __arm__
ptr hook_place_jump(ptr addr, ptr dest_cb) {

  size_t instr_len = 4;
  u32 displ = (dest_cb - addr) / instr_len;

  *(u32*)&addr[0] = displ;
  arr[3] = 0x14; // b jump
  
  return addr + instr_len;

}
#elif __aarch64__
ptr hook_place_jump(ptr addr, ptr dest_cb) {

  size_t instr_len = 4;
  u32 displ = (dest_cb - addr) / instr_len;

  *(u32*)&addr[0] = displ;
  addr[3] = 0x14; // b jump
  
  return addr + instr_len;

}
#else
#error "This arhcitecture is not supported!"
#endif