touch-packages team mailing list archive

[Seth Arnold <1452115@xxxxxxxxxxxxxxxxxx>]

We didn't enable PIE for the python interpreters for performance
reasons.

We're currently investigating turning PIE on by default for x86-64 and
other architectures that will likely handle it well. The performance
impact will be one of the deciding factors in determining if we enable
PIE for the python interpreter.

We're not likely to backport the PIE support to existing releases
because newer versions of GCC help reduce the performance penalty of
PIE compilation.

Thanks

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https://bugs.launchpad.net/bugs/1452115

Title:
  Python interpreter binary is not compiled as PIE

Status in python2.7 package in Ubuntu:
  Confirmed
Status in python3.4 package in Ubuntu:
  Confirmed

Bug description:
  The python2.7 binary (installed at /usr/bin/python2.7; package version
  2.7.6-8) is not compiled as a position independent executable (PIE).
  It appears that the python compilation process is somewhat arcane and
  the hardening wrapper probably doesn't do the trick for it.

  This is incredibly dangerous as it means that any vulnerability within
  a native module (e.g. ctypes-based), or within python itself will
  expose an incredibly large amount of known memory contents at known
  addresses (including a large number of dangerous instruction
  groupings). This enables ROP-based (https://en.wikipedia.org/wiki
  /Return-oriented_programming) to abuse the interpreter itself to
  bypass non-executable page protections.

  I have put together an example vulnerable C shared object (with a buffer overflow) accessed via python through the ctypes interface as an example. This uses a single ROP "gadget" on top of using the known PLT location for system(3) (https://en.wikipedia.org/wiki/Return-to-libc_attack) to call "id". The example code is accessible at:
  - https://gist.github.com/ChaosData/ae6076cb1c3cc7b0a367

  I'm not exactly familiar enough with the python build process to say
  where exactly an -fPIE needs to be injected into a script/makefile,
  but I feel that given the perceived general preference for ctypes-
  based modules over python written ones, as the native code
  implementations tend to be more performant, this feels like a large
  security hole within the system. Given the nature of this "issue," I'm
  not 100% sure of where it is best reported, but from what I can tell,
  this conflicts with the Ubuntu hardening features and is definitely
  exploitable should a native module contain a sufficiently exploitable
  vulnerability that allows for control of the instruction register.

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