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[Mathew Hodson <mathew.hodson@xxxxxxxxx>]

** Tags removed: verification-needed
** Tags added: verification-needed-utopic

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https://bugs.launchpad.net/bugs/1415481

Title:
  default mmap_min_addr for arm64 prevents running arm32 applications

Status in procps package in Ubuntu:
  Fix Released
Status in procps source package in Trusty:
  Fix Committed
Status in procps source package in Utopic:
  Fix Committed

Bug description:
  [ SRU Justification ]
  Executing 32-bit arm binaries as user fails on arm64.  Turns out, this is bad.

  [ Test Case ]
  Grab a 32-bit binary (either multiarch via armhf, or compile a quick static hello) and try to run it.  Also, check /proc/sys/vm/mmap_min_addr is set to 32k instead of 64k after boot.

  [ Regression Potential ]
  Shouldn't be any issue with 4k pagesize kernels, and this was already the default on 32-bit ARM for the same reasons.  It could, potentially, mean that the zero page is no longer entirely protected from mmap when running a 64k pagesize kernel, however we don't currently ship such a kernel, preferring instead to have 32-bit compatibility.

  [ Original Bug Report ]
  Executing 32-bit arm binaries as user fails on arm64:

  # file hello
  hello: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV),
  statically linked, for GNU/Linux 2.6.32,
  BuildID[sha1]=c37a3b366d645eee600963a535370fa0bad9b2c0, not stripped
  # ./hello
  hello world
  # su - linaro
  $ /root/hello
  Segmentation fault

  Root cause was identified to /etc/sysctl.d/10-zeropage.conf, which is
  set on arm64 to 65536. To run legacy binaries, this should be set to
  32768 like on armhf anr armel.

  Reference discussion:

  http://lists.infradead.org/pipermail/linux-arm-
  kernel/2015-January/320454.html

  Affects trusty, utopic and vivid

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