Problem With Cross-Compiling Cryptography for Android

[benfogle]

Problem With Cross-Compiling Cryptography for Android

[benfogle]

Can you give me a little bit more information about your build to help me reproduce the issue? What is:

• The architecture (arm?)
• The NDK version (21d?)
• The platform you are targeting.

The architecture is x86, the NDK version r21d (21.3.6528147), the platform is Android 26, Python version 3.5.3.

[benfogle]

When I try to reproduce this, I get the following:

(cross) $ pip install cryptography
Collecting cryptography==2.8
  Using cached https://files.pythonhosted.org/packages/45/73/d18a8884de8bffdcda475728008b5b13be7fbef40a2acc81a0d5d524175d/cryptography-2.8-cp34-abi3-manylinux1_x86_64.whl
Requirement already satisfied: six>=1.4.1 in ./cenv/cross/lib/python3.5/site-packages (from cryptography==2.8)
Requirement already satisfied: cffi!=1.11.3,>=1.8 in ./cenv/cross/lib/python3.5/site-packages (from cryptography==2.8)
Requirement already satisfied: pycparser in ./cenv/cross/lib/python3.5/site-packages (from cffi!=1.11.3,>=1.8->cryptography==2.8)
Installing collected packages: cryptography
Successfully installed cryptography-2.8
You are using pip version 9.0.1, however version 20.3.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

So it looks like pip isn't recognizing the difference between x86-linux-gnu and x86-linux-android, and it's grabbing the prebuilt Linux wheel from PyPi. This is something I'll need to look into, but in the mean time, you can work around it with:

$ pip install --no-binary=cryptography cryptography

(FYI: I found that upgrading pip caused some strange errors, so you might want to hold off.)

Thank you for the help! I used the recommended pip command and it seems to work. Now there is a different problem though:

from cryptography.hazmat.bindings._constant_time import lib
  File "<python>/importlib/_bootstrap.py", line 978, in _find_and_load
  File "<python>/importlib/_bootstrap.py", line 967, in _find_and_load_unlocked
  File "<python>/importlib/_bootstrap.py", line 666, in _load_unlocked
  File "<python>/importlib/_bootstrap.py", line 577, in module_from_spec
  File "<python>/importlib/_bootstrap_external.py", line 914, in create_module
  File "<python>/importlib/_bootstrap.py", line 222, in _call_with_frames_removed
ImportError: dlopen failed: cannot locate symbol "memset" referenced by "/data/tmp/lib/python3.5/site-packages/cryptography/hazmat/bindings/_constant_time.abi3.so"...

[benfogle]

I'm having trouble getting to a point that I can reproduce that error. Can you send me the output of readelf -lS --dyn-syms _constant_time.abi3.so?

There are 30 section headers, starting at offset 0x3d54:

Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
  [ 1] .interp           PROGBITS        00000114 000114 00003d 00   A  0   0  1
  [ 2] .dynsym           DYNSYM          00000154 000154 000120 10   A  3   1  4
  [ 3] .dynstr           STRTAB          00000274 000274 000119 00   A  0   0  1
  [ 4] .hash             HASH            00000390 000390 000094 04   A  2   0  4
  [ 5] .rel.dyn          REL             00000424 000424 000038 08   A  2   0  4
  [ 6] .rel.plt          REL             0000045c 00045c 000060 08  AI  2   7  4
  [ 7] .plt              PROGBITS        000004c0 0004c0 0000d0 04  AX  0   0 16
  [ 8] .text             PROGBITS        00000590 000590 000691 00  AX  0   0 16
  [ 9] .rodata           PROGBITS        00000c30 000c30 000093 00 AMS  0   0 16
  [10] .eh_frame         PROGBITS        00000cc4 000cc4 000040 00   A  0   0  4
  [11] .data.rel.ro      PROGBITS        00001f08 000f08 000054 00  WA  0   0  4
  [12] .dynamic          DYNAMIC         00001f5c 000f5c 000098 08  WA  3   0  4
  [13] .got              PROGBITS        00001ff4 000ff4 000000 00  WA  0   0  4
  [14] .got.plt          PROGBITS        00001ff4 000ff4 00003c 00  WA  0   0  4
  [15] .data             PROGBITS        00002030 001030 000024 00  WA  0   0  4
  [16] .bss              NOBITS          00002054 001054 000070 00  WA  0   0  4
  [17] .debug_str        PROGBITS        00000000 001054 000653 01  MS  0   0  1
  [18] .debug_loc        PROGBITS        00000000 0016a7 000672 00      0   0  1
  [19] .debug_abbrev     PROGBITS        00000000 001d19 0001f3 00      0   0  1
  [20] .debug_info       PROGBITS        00000000 001f0c 0009c8 00      0   0  1
  [21] .debug_ranges     PROGBITS        00000000 0028d4 0000b0 00      0   0  1
  [22] .debug_macinfo    PROGBITS        00000000 002984 000001 00      0   0  1
  [23] .comment          PROGBITS        00000000 002985 0000b6 01  MS  0   0  1
  [24] .debug_frame      PROGBITS        00000000 002a3c 0000f8 00      0   0  4
  [25] .debug_line       PROGBITS        00000000 002b34 000564 00      0   0  1
  [26] .note.gnu.go[...] NOTE            00000000 003098 00001c 00      0   0  4
  [27] .symtab           SYMTAB          00000000 0030b4 000980 10     28 135  4
  [28] .strtab           STRTAB          00000000 003a34 000205 00      0   0  1
  [29] .shstrtab         STRTAB          00000000 003c39 000118 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  p (processor specific)

Elf file type is DYN (Shared object file)
Entry point 0x0
There are 7 program headers, starting at offset 52

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x00000034 0x00000034 0x000e0 0x000e0 R   0x4
  INTERP         0x000114 0x00000114 0x00000114 0x0003d 0x0003d R   0x1
      [Requesting program interpreter: ~/Android/Sdk/ndk/21.3.6528147/sysroot/usr/include]
  LOAD           0x000000 0x00000000 0x00000000 0x00d04 0x00d04 R E 0x1000
  LOAD           0x000f08 0x00001f08 0x00001f08 0x0014c 0x001bc RW  0x1000
  DYNAMIC        0x000f5c 0x00001f5c 0x00001f5c 0x00098 0x00098 RW  0x4
  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x10
  GNU_RELRO      0x000f08 0x00001f08 0x00001f08 0x000f8 0x000f8 RW  0x4

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .interp 
   02     .interp .dynsym .dynstr .hash .rel.dyn .rel.plt .plt .text .rodata .eh_frame 
   03     .data.rel.ro .dynamic .got .got.plt .data .bss 
   04     .dynamic 
   05     
   06     .data.rel.ro .dynamic .got 

Symbol table '.dynsym' contains 18 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 00000590   273 FUNC    GLOBAL DEFAULT    8 Cryptography_con[...]
     2: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyArg_UnpackTuple
     3: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyErr_Occurred
     4: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyEval_RestoreThread
     5: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyEval_SaveThread
     6: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyImport_ImportModule
     7: 000006b0   191 FUNC    GLOBAL DEFAULT    8 PyInit__constant_time
     8: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyLong_FromLong
     9: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyLong_FromVoidPtr
    10: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyObject_CallMethod
    11: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyObject_Free
    12: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND PyObject_Malloc
    13: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND _Py_Dealloc
    14: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND memset
    15: 00002054     0 NOTYPE  GLOBAL DEFAULT  ABS _edata
    16: 00002054     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start
    17: 000020c4     0 NOTYPE  GLOBAL DEFAULT  ABS _end

[benfogle]

I'm not sure I can reproduce this, and it's certainly very odd that memset can't be found. It should be part of libc.

Maybe it's related to this?

Thank you for the help, I will give that a look.