IABSD.fr/src/libexec/ld.so/SPECS.randomdata

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• Author : mortimer
  Date : 2018-06-01 03:27:59
  Hash : 8b424531
  Message : Bump ELF_RANDOMIZE_LIMIT to 1MB. ok deraadt@

• libexec/ld.so/SPECS.randomdata

• $OpenBSD: SPECS.randomdata,v 1.3 2018/06/01 03:27:59 mortimer Exp $
  
  This document describes the OpenBSD operating system supplement for
  adding "random data" sections to the ELF ABI.  These sections can be
  useful for holding values like GCC's stack-smashing protector cookies
  and offer additional benefits like ensuring the data is initialized
  before any constructor methods are called and allowing the dynamic
  linker to mark the memory as read-only after initialization.
  
  
  Program Header
  
  OpenBSD defines the following operating system-specific segment type:
  
    Name                  Value
    PT_OPENBSD_RANDOMIZE  0x65a3dbe6
  
  
    PT_OPENBSD_RANDOMIZE
  
      The array element specifies the location and size of a random data
      section.  The system will initialize the specified memory range
      with random data.  The memory range must be separately mapped
      (e.g., by use of a PT_LOAD segment).
  
  
  Special Sections
  
  OpenBSD defines the following operating system-specific special
  sections:
  
    Name                 Type          Attributes
    .openbsd.randomdata  SHT_PROGBITS  SHF_ALLOC
  
  
    .openbsd.randomdata
  
      This section holds the random data section.
  
  
  Implementation Notes
  
  On OpenBSD, PT_OPENBSD_RANDOMIZE segments are handled alongside
  PT_LOAD segments: the kernel handles initializing random data segments
  in executables and program interpreters (i.e., ld.so), while ld.so
  handles initializing them in shared libraries.  Additionally, the
  kernel limits the total number of PT_OPENBSD_RANDOMIZE segment bytes
  in an executable or interpreter to 1048576 bytes.