tor-browser

BaseElf.cpp (6427B)

---

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "BaseElf.h"
#include "Elfxx.h"
#include "Logging.h"
#include "mozilla/IntegerPrintfMacros.h"
#include "mozilla/RefPtr.h"

using namespace Elf;

unsigned long BaseElf::Hash(const char* symbol) {
 const unsigned char* sym = reinterpret_cast<const unsigned char*>(symbol);
 unsigned long h = 0, g;
 while (*sym) {
   h = (h << 4) + *sym++;
   g = h & 0xf0000000;
   h ^= g;
   h ^= g >> 24;
 }
 return h;
}

void* BaseElf::GetSymbolPtr(const char* symbol) const {
 return GetSymbolPtr(symbol, Hash(symbol));
}

void* BaseElf::GetSymbolPtr(const char* symbol, unsigned long hash) const {
 const Sym* sym = GetSymbol(symbol, hash);
 void* ptr = nullptr;
 if (sym && sym->st_shndx != SHN_UNDEF) ptr = GetPtr(sym->st_value);
 DEBUG_LOG("BaseElf::GetSymbolPtr(%p [\"%s\"], \"%s\") = %p",
           reinterpret_cast<const void*>(this), GetPath(), symbol, ptr);
 return ptr;
}

const Sym* BaseElf::GetSymbol(const char* symbol, unsigned long hash) const {
 /* Search symbol with the buckets and chains tables.
  * The hash computed from the symbol name gives an index in the buckets
  * table. The corresponding value in the bucket table is an index in the
  * symbols table and in the chains table.
  * If the corresponding symbol in the symbols table matches, we're done.
  * Otherwise, the corresponding value in the chains table is a new index
  * in both tables, which corresponding symbol is tested and so on and so
  * forth */
 size_t bucket = hash % buckets.numElements();
 for (size_t y = buckets[bucket]; y != STN_UNDEF; y = chains[y]) {
   if (strcmp(symbol, strtab.GetStringAt(symtab[y].st_name))) continue;
   return &symtab[y];
 }
 return nullptr;
}

bool BaseElf::Contains(void* addr) const { return base.Contains(addr); }

#ifdef __ARM_EABI__
const void* BaseElf::FindExidx(int* pcount) const {
 if (arm_exidx) {
   *pcount = arm_exidx.numElements();
   return arm_exidx;
 }
 *pcount = 0;
 return nullptr;
}
#endif

already_AddRefed<LibHandle> LoadedElf::Create(const char* path,
                                             void* base_addr) {
 DEBUG_LOG("LoadedElf::Create(\"%s\", %p) = ...", path, base_addr);

 uint8_t mapped;
 /* If the page is not mapped, mincore returns an error. If base_addr is
  * nullptr, as would happen if the corresponding binary is prelinked with
  * the prelink look (but not with the android apriori tool), no page being
  * mapped there (right?), mincore returns an error, too, which makes
  * prelinked libraries on glibc unsupported. This is not an interesting
  * use case for now, so don't try supporting that case.
  */
 if (mincore(const_cast<void*>(base_addr), PageSize(), &mapped))
   return nullptr;

 RefPtr<LoadedElf> elf = new LoadedElf(path);

 const Ehdr* ehdr = Ehdr::validate(base_addr);
 if (!ehdr) return nullptr;

 Addr min_vaddr = (Addr)-1;  // We want to find the lowest and biggest
 Addr max_vaddr = 0;         // virtual address used by this Elf.
 const Phdr* dyn = nullptr;
#ifdef __ARM_EABI__
 const Phdr* arm_exidx_phdr = nullptr;
#endif

 Array<Phdr> phdrs(reinterpret_cast<const char*>(ehdr) + ehdr->e_phoff,
                   ehdr->e_phnum);
 for (auto phdr = phdrs.begin(); phdr < phdrs.end(); ++phdr) {
   switch (phdr->p_type) {
     case PT_LOAD:
       if (phdr->p_vaddr < min_vaddr) min_vaddr = phdr->p_vaddr;
       if (max_vaddr < phdr->p_vaddr + phdr->p_memsz)
         max_vaddr = phdr->p_vaddr + phdr->p_memsz;
       break;
     case PT_DYNAMIC:
       dyn = &*phdr;
       break;
#ifdef __ARM_EABI__
     case PT_ARM_EXIDX:
       /* We cannot initialize arm_exidx here
          because we don't have a base yet */
       arm_exidx_phdr = &*phdr;
       break;
#endif
   }
 }

 /* If the lowest PT_LOAD virtual address in headers is not 0, then the ELF
  * is either prelinked or a non-PIE executable. The former case is not
  * possible, because base_addr would be nullptr and the mincore test above
  * would already have made us return.
  * For a non-PIE executable, PT_LOADs contain absolute addresses, so in
  * practice, this means min_vaddr should be equal to base_addr. max_vaddr
  * can thus be adjusted accordingly.
  */
 if (min_vaddr != 0) {
   void* min_vaddr_ptr =
       reinterpret_cast<void*>(static_cast<uintptr_t>(min_vaddr));
   if (min_vaddr_ptr != base_addr) {
     LOG("%s: %p != %p", elf->GetPath(), min_vaddr_ptr, base_addr);
     return nullptr;
   }
   max_vaddr -= min_vaddr;
 }
 if (!dyn) {
   LOG("%s: No PT_DYNAMIC segment found", elf->GetPath());
   return nullptr;
 }

 elf->base.Assign(base_addr, max_vaddr);

 if (!elf->InitDyn(dyn)) return nullptr;

#ifdef __ARM_EABI__
 if (arm_exidx_phdr)
   elf->arm_exidx.InitSize(elf->GetPtr(arm_exidx_phdr->p_vaddr),
                           arm_exidx_phdr->p_memsz);
#endif

 DEBUG_LOG("LoadedElf::Create(\"%s\", %p) = %p", path, base_addr,
           static_cast<void*>(elf));

 ElfLoader::Singleton.Register(elf);
 return elf.forget();
}

bool LoadedElf::InitDyn(const Phdr* pt_dyn) {
 Array<Dyn> dyns;
 dyns.InitSize(GetPtr<Dyn>(pt_dyn->p_vaddr), pt_dyn->p_filesz);

 size_t symnum = 0;
 for (auto dyn = dyns.begin(); dyn < dyns.end() && dyn->d_tag; ++dyn) {
   switch (dyn->d_tag) {
     case DT_HASH: {
       DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_HASH", uintptr_t(dyn->d_un.d_val));
       const Elf::Word* hash_table_header = GetPtr<Elf::Word>(dyn->d_un.d_ptr);
       symnum = hash_table_header[1];
       buckets.Init(&hash_table_header[2], hash_table_header[0]);
       chains.Init(&*buckets.end());
     } break;
     case DT_STRTAB:
       DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_STRTAB", uintptr_t(dyn->d_un.d_val));
       strtab.Init(GetPtr(dyn->d_un.d_ptr));
       break;
     case DT_SYMTAB:
       DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_SYMTAB", uintptr_t(dyn->d_un.d_val));
       symtab.Init(GetPtr(dyn->d_un.d_ptr));
       break;
   }
 }
 if (!buckets || !symnum) {
   ERROR("%s: Missing or broken DT_HASH", GetPath());
 } else if (!strtab) {
   ERROR("%s: Missing DT_STRTAB", GetPath());
 } else if (!symtab) {
   ERROR("%s: Missing DT_SYMTAB", GetPath());
 } else {
   return true;
 }
 return false;
}