VitaShell/elf.c

/*
  VitaShell
  Copyright (C) 2015-2018, TheFloW

  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "main.h"
#include "elf.h"

//! Module Information
typedef struct {
  uint16_t attr;  //!< Attribute
  uint16_t ver;  //!< Version
  char name[27];  //!< Name
  uint8_t type;  //!< Type
  void *gp;  //!< Global Pointer
  uint32_t expTop;  //!< Offset of the top of export table
  uint32_t expBtm;  //!< Offset of the bottom of export table
  uint32_t impTop;  //!< Offset of the top of import table
  uint32_t impBtm;  //!< Offset of the bottom of import table
  uint32_t nid;  //!< NID
  uint32_t unk[3];  //!< Unknown
  uint32_t start;  //!< Offset of module_start function
  uint32_t stop;  //!< Offset of module_stop function
  uint32_t exidxTop;  //!< Offset of the top of exidx section
  uint32_t exidxBtm;  //!< Offset of the bottom of exidx section
  uint32_t extabTop;  //!< Offset of the top of extab section
  uint32_t extabBtm;  //!< Offset of the bottom of extab section
} SceModuleInfo;

typedef struct {
  uint16_t size;
  uint16_t lib_version;
  uint16_t attribute;
  uint16_t num_functions;
  uint16_t num_vars;
  uint16_t num_tls_vars;
  uint32_t reserved1;
  uint32_t module_nid;
  char *lib_name;
  uint32_t reserved2;
  uint32_t func_nid_table;
  uint32_t func_entry_table;
  uint32_t var_nid_table;
  uint32_t var_entry_table;
  uint32_t tls_nid_table;
  uint32_t tls_entry_table;
} SceImportsTable2xx;

typedef struct {
  uint16_t size;
  uint16_t lib_version;
  uint16_t attribute;
  uint16_t num_functions;
  uint16_t num_vars;
  uint16_t unknown1;
  uint32_t module_nid;
  char *lib_name;
  uint32_t func_nid_table;
  uint32_t func_entry_table;
  uint32_t var_nid_table;
  uint32_t var_entry_table;
} SceImportsTable3xx;

void convertToImportsTable3xx(SceImportsTable2xx *import_2xx, SceImportsTable3xx *import_3xx) {
  memset(import_3xx, 0, sizeof(SceImportsTable3xx));

  if (import_2xx->size == sizeof(SceImportsTable2xx)) {
    import_3xx->size = import_2xx->size;
    import_3xx->lib_version = import_2xx->lib_version;
    import_3xx->attribute = import_2xx->attribute;
    import_3xx->num_functions = import_2xx->num_functions;
    import_3xx->num_vars = import_2xx->num_vars;
    import_3xx->module_nid = import_2xx->module_nid;
    import_3xx->lib_name = import_2xx->lib_name;
    import_3xx->func_nid_table = import_2xx->func_nid_table;
    import_3xx->func_entry_table = import_2xx->func_entry_table;
    import_3xx->var_nid_table = import_2xx->var_nid_table;
    import_3xx->var_entry_table = import_2xx->var_entry_table;
  } else if (import_2xx->size == sizeof(SceImportsTable3xx)) {
    memcpy(import_3xx, import_2xx, sizeof(SceImportsTable3xx));
  }
}

int checkForUnsafeImports(void *buffer) {
  Elf32_Ehdr *ehdr = (Elf32_Ehdr *)buffer;
  Elf32_Phdr *phdr = (Elf32_Phdr *)((uint32_t)buffer + ehdr->e_phoff);

  if (ehdr->e_ident[EI_MAG0] != ELFMAG0 ||
      ehdr->e_ident[EI_MAG1] != ELFMAG1 ||
      ehdr->e_ident[EI_MAG2] != ELFMAG2 ||
      ehdr->e_ident[EI_MAG3] != ELFMAG3) {
    return VITASHELL_ERROR_INVALID_MAGIC;
  }

  uint32_t segment = ehdr->e_entry >> 30;
  uint32_t offset = ehdr->e_entry & 0x3FFFFFFF;

  uint32_t text_addr = (uint32_t)buffer + phdr[segment].p_offset;

  SceModuleInfo *mod_info = (SceModuleInfo *)(text_addr + offset);

  int has_dangerous_nids = 0;
  int has_unsafe_libraries = 0;

  uint32_t i = mod_info->impTop;
  while (i < mod_info->impBtm) {
    SceImportsTable3xx import;
    convertToImportsTable3xx((void *)text_addr + i, &import);

    char *libname = (char *)(text_addr + import.lib_name - phdr[segment].p_vaddr);
    uint32_t *func_nid_table = (uint32_t *)(text_addr + import.func_nid_table - phdr[segment].p_vaddr);

    if (strcmp(libname, "SceVshBridge") == 0) {
      int j;
      for (j = 0; j < import.num_functions; j++) {
        // Check for dangerous _vshIoMount/vshIoUmount
        if (func_nid_table[j] == 0x3C522C35 || func_nid_table[j] == 0x35BC26AC) {
          has_dangerous_nids = 1;
          break;
        }
      }
    } else if (strcmp(libname, "ScePromoterUtil") == 0 || strcmp(libname, "SceShellSvc") == 0) {
      has_unsafe_libraries = 1;
    }

    i += import.size;
  }

  if (has_dangerous_nids)
    return 2; // Really not safe bro
  
  if (has_unsafe_libraries)
    return 1; // Unsafe, but won't kill you

  return 0; // Safe
}

char *uncompressBuffer(const Elf32_Ehdr *ehdr, const Elf32_Phdr *phdr, const segment_info *segment,
         const char *buffer) {
  if (ehdr->e_ident[EI_MAG0] != ELFMAG0 ||
      ehdr->e_ident[EI_MAG1] != ELFMAG1 ||
      ehdr->e_ident[EI_MAG2] != ELFMAG2 ||
      ehdr->e_ident[EI_MAG3] != ELFMAG3) {
    return NULL;
  }

  int i;
  // sum all segment size
  uint32_t total_sz = 0;
  for (i = 0; i < ehdr->e_phnum; i++) {
    total_sz += (phdr + i)->p_filesz;
  }

  char *out = malloc(total_sz);
  if (out == NULL) {
    return NULL;
  }

  // uncompress each segments
  char *buf = out;
  for (i = 0; i < ehdr->e_phnum; i++) {
    uint64_t offset = (segment + i)->offset - segment->offset;
    uint32_t size = (phdr + i)->p_filesz;

    if ((segment + i)->compression == 1) {
      memcpy(buf, buffer + offset, (segment + i)->length);
      buf += size;
      continue;
    }
    uLongf buf_len = size;
    int ret = uncompress((Bytef *)buf, &buf_len, (const Bytef *)buffer + offset, (segment + i)->length);
    if (ret != Z_OK) {
      free(out);
      return NULL;
    }
    buf += size;
  }
  return out;
}