Android: Add chrome-specific dynamic linker.

base/android/linker/crazy_linker/src/crazy_linker_elf_loader.cpp

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "crazy_linker_elf_loader.h"
+
+#include <limits.h>  // For PAGE_SIZE and PAGE_MASK
+
+#include "crazy_linker_debug.h"
+#include "linker_phdr.h"
+
+#define PAGE_START(x)  ((x) & PAGE_MASK)
+#define PAGE_OFFSET(x) ((x) & ~PAGE_MASK)
+#define PAGE_END(x)    PAGE_START((x) + (PAGE_SIZE-1))
+
+namespace crazy {
+
+#define MAYBE_MAP_FLAG(x,from,to)    (((x) & (from)) ? (to) : 0)
+#define PFLAGS_TO_PROT(x)            (MAYBE_MAP_FLAG((x), PF_X, PROT_EXEC) | \
+                                      MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
+                                      MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
+
+ElfLoader::ElfLoader()
+  : fd_(),
+    path_(NULL),
+    phdr_num_(0),
+    phdr_mmap_(NULL),
+    phdr_table_(NULL),
+    phdr_size_(0),
+    file_offset_(0),
+    wanted_load_address_(0),
+    load_start_(NULL),
+    load_size_(0),
+    load_bias_(0),
+    loaded_phdr_(NULL) {
+}
+
+ElfLoader::~ElfLoader() {
+  if (phdr_mmap_) {
+    // Deallocate the temporary program header copy.
+    munmap(phdr_mmap_, phdr_size_);
+  }
+}
+
+bool ElfLoader::LoadAt(const char* lib_path,
+                       off_t       file_offset,
+                       uintptr_t   wanted_address,
+                       Error*      error) {
+
+  LOG("%s: lib_path='%s', file_offset=%p, load_address=%p\n",
+      __FUNCTION__, lib_path, file_offset, wanted_address);
+
+  // Check that the load address is properly page-aligned.
+  if (wanted_address != PAGE_START(wanted_address)) {
+    error->Format("Load address is not page aligned (%08x)",
+                    wanted_address);
+    return false;
+  }
+  wanted_load_address_ = reinterpret_cast<void*>(wanted_address);
+
+  // Check that the file offset is also properly page-aligned.
+  if (file_offset != PAGE_START(file_offset)) {
+    error->Format("File offset is not page aligned (%08x)",
+                  file_offset);
+    return false;
+  }
+  file_offset_ = file_offset;
+
+  // Open the file.
+  if (!fd_.OpenReadOnly(lib_path)) {
+    error->Format("Can't open file: %s", strerror(errno));
+    return false;
+  }
+
+  if (file_offset && fd_.SeekTo(file_offset) < 0) {
+    error->Format("Can't seek to file offset %08x: %s",
+                  file_offset, strerror(errno));
+    return false;
+  }
+
+  path_ = lib_path;
+
+  if (!ReadElfHeader(error) ||
+      !ReadProgramHeader(error) ||
+      !ReserveAddressSpace(error)) {
+    return false;
+  }
+
+  if (!LoadSegments(error) || !FindPhdr(error)) {
+    // An error occured, cleanup the address space by un-mapping the
+    // range that was reserved by ReserveAddressSpace().
+    if (load_start_ && load_size_)
+      munmap(load_start_, load_size_);
+
+    return false;
+  }
+
+  return true;
+}
+
+bool ElfLoader::ReadElfHeader(Error* error) {
+  int ret = fd_.Read(&header_, sizeof(header_));
+  if (ret < 0) {
+    error->Format("Can't read file: %s", strerror(errno));
+    return false;
+  }
+  if (ret != static_cast<int>(sizeof(header_))) {
+    error->Set("File too small to be ELF");
+    return false;
+  }
+
+  if (header_.e_ident[EI_MAG0] != ELFMAG0 ||
+      header_.e_ident[EI_MAG1] != ELFMAG1 ||
+      header_.e_ident[EI_MAG2] != ELFMAG2 ||
+      header_.e_ident[EI_MAG3] != ELFMAG3) {
+    error->Set("Bad ELF magic");
+    return false;
+  }
+
+  if (header_.e_ident[EI_CLASS] != ELFCLASS32) {
+    error->Format("Not a 32-bit class: %d",
+                    header_.e_ident[EI_CLASS]);
+    return false;
+  }
+  if (header_.e_ident[EI_DATA] != ELFDATA2LSB) {
+    error->Format("Not little-endian class: %d",
+                    header_.e_ident[EI_DATA]);
+    return false;
+  }
+
+  if (header_.e_type != ET_DYN) {
+    error->Format("Not a shared library type: %d",
+                    header_.e_type);
+    return false;
+  }
+
+  if (header_.e_version != EV_CURRENT) {
+    error->Format("Unexpected ELF version: %d",
+                    header_.e_version);
+    return false;
+  }
+
+  if (header_.e_machine != ELF_MACHINE) {
+    error->Format("Unexpected ELF machine type: %d",
+                    header_.e_machine);
+    return false;
+  }
+
+  return true;
+}
+
+// Loads the program header table from an ELF file into a read-only private
+// anonymous mmap-ed block.
+bool ElfLoader::ReadProgramHeader(Error* error) {
+  phdr_num_ = header_.e_phnum;
+
+  // Like the kernel, only accept program header tables smaller than 64 KB.
+  if (phdr_num_ < 1 || phdr_num_ > 65536/sizeof(ELF::Phdr)) {
+    error->Format("Invalid program header count: %d", phdr_num_);
+    return false;
+  }
+
+  ELF::Addr page_min = PAGE_START(header_.e_phoff);
+  ELF::Addr page_max =
+      PAGE_END(header_.e_phoff + (phdr_num_ * sizeof(ELF::Phdr)));
+  ELF::Addr page_offset = PAGE_OFFSET(header_.e_phoff);
+
+  phdr_size_ = page_max - page_min;
+
+  void* mmap_result = fd_.Map(NULL,
+                              phdr_size_,
+                              PROT_READ,
+                              MAP_PRIVATE,
+                              page_min + file_offset_);
+  if (mmap_result == MAP_FAILED) {
+    error->Format("Phdr mmap failed: %s", strerror(errno));
+    return false;
+  }
+
+  phdr_mmap_ = mmap_result;
+  phdr_table_ = reinterpret_cast<ELF::Phdr*>(
+      reinterpret_cast<char*>(mmap_result) + page_offset);
+  return true;
+}
+
+// Reserve a virtual address range big enough to hold all loadable
+// segments of a program header table. This is done by creating a
+// private anonymous mmap() with PROT_NONE.
+//
+// This will use the wanted_load_address_ value,
+bool ElfLoader::ReserveAddressSpace(Error* error) {
+  ELF::Addr min_vaddr;
+  load_size_ =
+      phdr_table_get_load_size(phdr_table_, phdr_num_, &min_vaddr, NULL);
+  if (load_size_ == 0) {
+    error->Set("No loadable segments");
+    return false;
+  }
+
+  uint8_t* addr = reinterpret_cast<uint8_t*>(min_vaddr);
+  int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
+
+  // Support loading at a fixed address.
+  if (wanted_load_address_) {
+    addr = static_cast<uint8_t*>(wanted_load_address_);
+    mmap_flags |= MAP_FIXED;
+  }
+
+  LOG("%s: address=%p size=%p\n", __FUNCTION__, addr, load_size_);
+  void* start = mmap(addr, load_size_, PROT_NONE, mmap_flags, -1, 0);
+  if (start == MAP_FAILED) {
+    error->Format("Could not reserve %d bytes of address space",
+                    load_size_);
+    return false;
+  }
+
+  load_start_ = start;
+  load_bias_ = reinterpret_cast<ELF::Addr>(start) - min_vaddr;
+  return true;
+}
+
+// Returns the address of the program header table as it appears in the loaded
+// segments in memory. This is in contrast with 'phdr_table_' which
+// is temporary and will be released before the library is relocated.
+bool ElfLoader::FindPhdr(Error* error) {
+  const ELF::Phdr* phdr_limit = phdr_table_ + phdr_num_;
+
+  // If there is a PT_PHDR, use it directly.
+  for (const ELF::Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+    if (phdr->p_type == PT_PHDR) {
+      return CheckPhdr(load_bias_ + phdr->p_vaddr, error);
+    }
+  }
+
+  // Otherwise, check the first loadable segment. If its file offset
+  // is 0, it starts with the ELF header, and we can trivially find the
+  // loaded program header from it.
+  for (const ELF::Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+    if (phdr->p_type == PT_LOAD) {
+      if (phdr->p_offset == 0) {
+        ELF::Addr  elf_addr = load_bias_ + phdr->p_vaddr;
+        const ELF::Ehdr* ehdr = (const ELF::Ehdr*)(void*)elf_addr;
+        ELF::Addr  offset = ehdr->e_phoff;
+        return CheckPhdr((ELF::Addr)ehdr + offset, error);
+      }
+      break;
+    }
+  }
+
+  error->Set("Can't find loaded program header");
+  return false;
+}
+
+// Ensures that our program header is actually within a loadable
+// segment. This should help catch badly-formed ELF files that
+// would cause the linker to crash later when trying to access it.
+bool ElfLoader::CheckPhdr(ELF::Addr loaded, Error* error) {
+  const ELF::Phdr* phdr_limit = phdr_table_ + phdr_num_;
+  ELF::Addr loaded_end = loaded + (phdr_num_ * sizeof(ELF::Phdr));
+  for (ELF::Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+    if (phdr->p_type != PT_LOAD) {
+      continue;
+    }
+    ELF::Addr seg_start = phdr->p_vaddr + load_bias_;
+    ELF::Addr seg_end = phdr->p_filesz + seg_start;
+    if (seg_start <= loaded && loaded_end <= seg_end) {
+      loaded_phdr_ = reinterpret_cast<const ELF::Phdr*>(loaded);
+      return true;
+    }
+  }
+  error->Format("Loaded program header %x not in loadable segment",
+                  loaded);
+  return false;
+}
+
+// Map all loadable segments in process' address space.
+// This assumes you already called phdr_table_reserve_memory to
+// reserve the address space range for the library.
+bool ElfLoader::LoadSegments(Error* error) {
+  for (size_t i = 0; i < phdr_num_; ++i) {
+    const ELF::Phdr* phdr = &phdr_table_[i];
+
+    if (phdr->p_type != PT_LOAD) {
+      continue;
+    }
+
+    // Segment addresses in memory.
+    ELF::Addr seg_start = phdr->p_vaddr + load_bias_;
+    ELF::Addr seg_end   = seg_start + phdr->p_memsz;
+
+    ELF::Addr seg_page_start = PAGE_START(seg_start);
+    ELF::Addr seg_page_end   = PAGE_END(seg_end);
+
+    ELF::Addr seg_file_end   = seg_start + phdr->p_filesz;
+
+    // File offsets.
+    ELF::Addr file_start = phdr->p_offset;
+    ELF::Addr file_end   = file_start + phdr->p_filesz;
+
+    ELF::Addr file_page_start = PAGE_START(file_start);
+    ELF::Addr file_length = file_end - file_page_start;
+
+    LOG("%s: file_offset=%p file_length=%p start_address=%p end_address=%p\n",
+        __FUNCTION__, file_offset_ + file_page_start,
+        file_length, seg_page_start, seg_page_start + PAGE_END(file_length));
+
+    if (file_length != 0) {
+      void* seg_addr = fd_.Map((void*)seg_page_start,
+                               file_length,
+                               PFLAGS_TO_PROT(phdr->p_flags),
+                               MAP_FIXED|MAP_PRIVATE,
+                               file_page_start + file_offset_);
+      if (seg_addr == MAP_FAILED) {
+        error->Format("Could not map segment %d: %s", i, strerror(errno));
+        return false;
+      }
+    }
+
+    // if the segment is writable, and does not end on a page boundary,
+    // zero-fill it until the page limit.
+    if ((phdr->p_flags & PF_W) != 0 && PAGE_OFFSET(seg_file_end) > 0) {
+      memset((void*)seg_file_end, 0, PAGE_SIZE - PAGE_OFFSET(seg_file_end));
+    }
+
+    seg_file_end = PAGE_END(seg_file_end);
+
+    // seg_file_end is now the first page address after the file
+    // content. If seg_end is larger, we need to zero anything
+    // between them. This is done by using a private anonymous
+    // map for all extra pages.
+    if (seg_page_end > seg_file_end) {
+      void* zeromap = mmap((void*)seg_file_end,
+                           seg_page_end - seg_file_end,
+                           PFLAGS_TO_PROT(phdr->p_flags),
+                           MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
+                           -1,
+                           0);
+      if (zeromap == MAP_FAILED) {
+        error->Format("Could not zero-fill gap: %s", strerror(errno));
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+}  // namespace crazy