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