…ty-check.py

5ca90f8 scripts: add MACHO lazy bindings check to security-check.py (fanquake)

Pull request description:

  This is a slightly belated follow up to bitcoin#17686 and some discussion with Cory. It's not entirely clear if we should make this change due to the way the macOS dynamic loader appears to work. However I'm opening this for some discussion. Also related to bitcoin#17768.

  #### Issue:
  [`LD64`](https://opensource.apple.com/source/ld64/) doesn't set the [MH_BINDATLOAD](https://opensource.apple.com/source/xnu/xnu-6153.11.26/EXTERNAL_HEADERS/mach-o/loader.h.auto.html) bit in the header of MACHO executables, when building with `-bind_at_load`. This is in contradiction to the [documentation](https://opensource.apple.com/source/ld64/ld64-450.3/doc/man/man1/ld.1.auto.html):
  ```bash
  -bind_at_load
       Sets a bit in the mach header of the resulting binary which tells dyld to
       bind all symbols when the binary is loaded, rather than lazily.
  ```

  The [`ld` in Apples cctools](https://opensource.apple.com/source/cctools/cctools-927.0.2/ld/layout.c.auto.html) does set the bit, however the [cctools-port](https://github.com/tpoechtrager/cctools-port/) that we use for release builds, bundles `LD64`.

  However; even if the linker hasn't set that bit, the dynamic loader ([`dyld`](https://opensource.apple.com/source/dyld/)) doesn't seem to ever check for it, and from what I understand, it looks at a different part of the header when determining whether to lazily load symbols.

  Note that our release binaries are currently working as expected, and no lazy loading occurs.

  #### Example:

  Using a small program, we can observe the behaviour of the dynamic loader.

  Conducted using:
  ```bash
  clang++ --version
  Apple clang version 11.0.0 (clang-1100.0.33.17)
  Target: x86_64-apple-darwin18.7.0

  ld -v
  @(#)PROGRAM:ld  PROJECT:ld64-530
  BUILD 18:57:17 Dec 13 2019
  LTO support using: LLVM version 11.0.0, (clang-1100.0.33.17) (static support for 23, runtime is 23)
  TAPI support using: Apple TAPI version 11.0.0 (tapi-1100.0.11)
  ```

  ```cpp
  #include <iostream>
  int main() {
  	std::cout << "Hello World!\n";
  	return 0;
  }
  ```

  Compile and check the MACHO header:
  ```bash
  clang++ test.cpp -o test
  otool -vh test
  ...
  Mach header
        magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
  MH_MAGIC_64  X86_64        ALL LIB64     EXECUTE    16       1424   NOUNDEFS DYLDLINK TWOLEVEL WEAK_DEFINES BINDS_TO_WEAK PIE

  # Run and dump dynamic loader bindings:
  DYLD_PRINT_BINDINGS=1 DYLD_PRINT_TO_FILE=no_bind.txt ./test
  Hello World!
  ```

  Recompile with `-bind_at_load`. Note still no `BINDATLOAD` flag:
  ```bash
  clang++ test.cpp -o test -Wl,-bind_at_load
  otool -vh test
  Mach header
        magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
  MH_MAGIC_64  X86_64        ALL LIB64     EXECUTE    16       1424   NOUNDEFS DYLDLINK TWOLEVEL WEAK_DEFINES BINDS_TO_WEAK PIE
  ...
  DYLD_PRINT_BINDINGS=1 DYLD_PRINT_TO_FILE=bind.txt ./test
  Hello World!
  ```

  If we diff the outputs, you can see that `dyld` doesn't perform any lazy bindings when the binary is compiled with `-bind_at_load`, even if the `BINDATLOAD` flag is not set:
  ```diff
  @@ -1,11 +1,27 @@
  +dyld: bind: test:0x103EDF030 = libc++.1.dylib:__ZNKSt3__16locale9use_facetERNS0_2idE, *0x103EDF030 = 0x7FFF70C9FA58
  +dyld: bind: test:0x103EDF038 = libc++.1.dylib:__ZNKSt3__18ios_base6getlocEv, *0x103EDF038 = 0x7FFF70CA12C2
  +dyld: bind: test:0x103EDF068 = libc++.1.dylib:__ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE6sentryC1ERS3_, *0x103EDF068 = 0x7FFF70CA12B6
  +dyld: bind: test:0x103EDF070 = libc++.1.dylib:__ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE6sentryD1Ev, *0x103EDF070 = 0x7FFF70CA1528
  +dyld: bind: test:0x103EDF080 = libc++.1.dylib:__ZNSt3__16localeD1Ev, *0x103EDF080 = 0x7FFF70C9FAE6
  <trim>
  -dyld: lazy bind: test:0x10D4AC0C8 = libsystem_platform.dylib:_strlen, *0x10D4AC0C8 = 0x7FFF73C5C6E0
  -dyld: lazy bind: test:0x10D4AC068 = libc++.1.dylib:__ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE6sentryC1ERS3_, *0x10D4AC068 = 0x7FFF70CA12B6
  -dyld: lazy bind: test:0x10D4AC038 = libc++.1.dylib:__ZNKSt3__18ios_base6getlocEv, *0x10D4AC038 = 0x7FFF70CA12C2
  -dyld: lazy bind: test:0x10D4AC030 = libc++.1.dylib:__ZNKSt3__16locale9use_facetERNS0_2idE, *0x10D4AC030 = 0x7FFF70C9FA58
  -dyld: lazy bind: test:0x10D4AC080 = libc++.1.dylib:__ZNSt3__16localeD1Ev, *0x10D4AC080 = 0x7FFF70C9FAE6
  -dyld: lazy bind: test:0x10D4AC070 = libc++.1.dylib:__ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE6sentryD1Ev, *0x10D4AC070 = 0x7FFF70CA1528
  ```

  Note: `dyld` also has a `DYLD_BIND_AT_LAUNCH=1` environment variable, that when set, will force any lazy bindings to be non-lazy:
  ```bash
  dyld: forced lazy bind: test:0x10BEC8068 = libc++.1.dylib:__ZNSt3__113basic_ostream
  ```

  #### Thoughts:
  After looking at the dyld source, I can't find any checks for `MH_BINDATLOAD`. You can see the flags it does check for, such as MH_PIE or MH_BIND_TO_WEAK [here](https://opensource.apple.com/source/dyld/dyld-732.8/src/ImageLoaderMachO.cpp.auto.html).

  It seems that the lazy binding of any symbols depends on whether or not [lazy_bind_size](https://opensource.apple.com/source/xnu/xnu-6153.11.26/EXTERNAL_HEADERS/mach-o/loader.h.auto.html) from the `LC_DYLD_INFO_ONLY` load command is > 0. Which was mentioned in [bitcoin#17686](bitcoin#17686 (comment)).

  #### Changes:
  This PR is one of [Corys commits](theuni@7b6ba26), that I've rebased and modified to make build. I've also included an addition to the `security-check.py` script to check for the flag.

  However, given the above, I'm not entirely sure this patch is the correct approach. If the linker no-longer inserts it, and the dynamic loader doesn't look for it, there might be little benefit to setting it. Or, maybe this is an oversight from Apple and needs some upstream discussion. Looking for some thoughts / Concept ACK/NACK.

  One alternate approach we could take is to drop the patch and modify security-check.py to look for `lazy_bind_size` == 0 in the `LC_DYLD_INFO_ONLY` load command, using `otool -l`.

ACKs for top commit:
  theuni:
    ACK 5ca90f8

Tree-SHA512: 444022ea9d19ed74dd06dc2ab3857a9c23fbc2f6475364e8552d761b712d684b3a7114d144f20de42328d1a99403b48667ba96885121392affb2e05b834b6e1c

I didn't add the relevant test in bitcoin#18295.

8334ee3 scripts: add MACHO LAZY_BINDINGS test to test-security-check.py (fanquake)
7b99c74 scripts: add MACHO Canary check to security-check.py (fanquake)

Pull request description:

  7b99c74 uses `otool -Iv` to check for `___stack_chk_fail` in the macOS binaries. Similar to the [ELF check](https://github.com/bitcoin/bitcoin/blob/master/contrib/devtools/security-check.py#L105). Note that looking for a triple underscore prefixed function (as opposed to two for ELF) is correct for the macOS binaries. i.e:
  ```bash
  otool -Iv bitcoind | grep chk
  0x00000001006715b8   509 ___memcpy_chk
  0x00000001006715be   510 ___snprintf_chk
  0x00000001006715c4   511 ___sprintf_chk
  0x00000001006715ca   512 ___stack_chk_fail
  0x00000001006715d6   517 ___vsnprintf_chk
  0x0000000100787898   513 ___stack_chk_guard
  ```

  8334ee3 is a follow up to #18295 and adds test cases to `test-security-check.py` that for some reason I didn't add at the time. I'll sort out #18434 so that we can run these tests in the CI.

ACKs for top commit:
  practicalswift:
    ACK 8334ee3: Mitigations are important. Important things are worth asserting :)
  jonasschnelli:
    utACK 8334ee3.

Tree-SHA512: 1aa5ded34bbd187eddb112b27278deb328bfc21ac82316b20fab6ad894f223b239a76b53dab0ac1770d194c1760fcc40d4da91ec09959ba4fc8eadedb173936a

I didn't add the relevant test in bitcoin#18295.