1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef CRAZY_LINKER_ELF_RELRO_H
6 #define CRAZY_LINKER_ELF_RELRO_H
7 
8 #include "crazy_linker_ashmem.h"
9 #include "crazy_linker_memory_mapping.h"
10 #include "crazy_linker_system.h"
11 #include "elf_traits.h"
12 
13 namespace crazy {
14 
15 class ElfView;
16 
17 // A class used to model a shared RELRO section backed by an Ashmem region.
18 // The region is always owned by the SharedRelro, unless DetachFd() is called.
19 // The SharedRelro may or may not be mapped into the process.
20 class SharedRelro {
21  public:
22   // Create a new SharedRelro. Note that the object becomes the owner of
23   // |ashmem_fd|, unless DetachFd() is called after this.
SharedRelro()24   SharedRelro() : start_(0), size_(0), ashmem_() {}
25 
~SharedRelro()26   ~SharedRelro() {}
27 
start()28   size_t start() const { return start_; }
end()29   size_t end() const { return start_ + size_; }
size()30   size_t size() const { return size_; }
fd()31   int fd() const { return ashmem_.fd(); }
32 
33   // Return the ashmem region's file descriptor, and detach it from the object.
34   // After this call, fd() will always return -1.
DetachFd()35   int DetachFd() { return ashmem_.Release(); }
36 
37   // Allocate a new ashmem region of |relro_size| bytes for |library_name|.
38   // This operation doesn't change the process' mappings. On error, return
39   // false and set |error| message.
40   bool Allocate(size_t relro_size, const char* library_name, Error* error);
41 
42   // Copy the content of the current process' RELRO into the ashmem region.
43   // |relro_start| is the RELRO address (page-aligned).
44   // |relro_size| is the RELRO size in bytes (page-aligned), and must match
45   // the allocation size passed to Allocate().
46   // On failure, return false and set |error| message.
47   bool CopyFrom(size_t relro_start, size_t relro_size, Error* error);
48 
49   // Copy the contents of the current process' RELRO into the ashmem region
50   // but adjust any relocation targets within it to correspond to a new
51   // |load_address|. |view| must point to a mapped ELF binary for the current
52   // library. |relro_start| corresponds to the address of the current
53   // process' RELRO, i.e. is not relocated.
54   bool CopyFromRelocated(const ElfView* view,
55                          size_t load_address,
56                          size_t relro_start,
57                          size_t relro_size,
58                          Error* error);
59 
60   // Force the section to be read-only.
61   bool ForceReadOnly(Error* error);
62 
63   // Map the ashmem region's pages into the current process, doing a comparison
64   // to avoid corrupting parts of the RELRO section that are different in this
65   // one (e.g. due to symbolic relocations to randomized system libraries).
66   // This operation is _not_ atomic, i.e. no other thread should try to execute
67   // code that reads from the RELRO region during this call.
68   // On failure, return false and set |error| message.
69   // This operation does not transfer ownership of |ashmem_fd| to the object.
70   bool InitFrom(size_t relro_start,
71                 size_t relro_size,
72                 int ashmem_fd,
73                 Error* error);
74 
75  private:
76   size_t start_;
77   size_t size_;
78   AshmemRegion ashmem_;
79 };
80 
81 }  // namespace crazy
82 
83 #endif  // CRAZY_LINKER_ELF_RELRO_H
84