android_kernel_xiaomi_sm7250/security/Kconfig.hardening

# SPDX-License-Identifier: GPL-2.0-only
menu "Kernel hardening options"

config GCC_PLUGIN_STRUCTLEAK
	bool
	help
	  While the kernel is built with warnings enabled for any missed
	  stack variable initializations, this warning is silenced for
	  anything passed by reference to another function, under the
	  occasionally misguided assumption that the function will do
	  the initialization. As this regularly leads to exploitable
	  flaws, this plugin is available to identify and zero-initialize
	  such variables, depending on the chosen level of coverage.

	  This plugin was originally ported from grsecurity/PaX. More
	  information at:
	   * https://grsecurity.net/
	   * https://pax.grsecurity.net/

menu "Memory initialization"

config CC_HAS_AUTO_VAR_INIT_PATTERN
	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)

config CC_HAS_AUTO_VAR_INIT_ZERO_BARE
	def_bool $(cc-option,-ftrivial-auto-var-init=zero)

config CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER
	# Clang 16 and later warn about using the -enable flag, but it
	# is required before then.
	def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)
	depends on !CC_HAS_AUTO_VAR_INIT_ZERO_BARE

config CC_HAS_AUTO_VAR_INIT_ZERO
	def_bool CC_HAS_AUTO_VAR_INIT_ZERO_BARE || CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER

choice
	prompt "Initialize kernel stack variables at function entry"
	default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
	default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
	default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
	default INIT_STACK_NONE
	help
	  This option enables initialization of stack variables at
	  function entry time. This has the possibility to have the
	  greatest coverage (since all functions can have their
	  variables initialized), but the performance impact depends
	  on the function calling complexity of a given workload's
	  syscalls.

	  This chooses the level of coverage over classes of potentially
	  uninitialized variables. The selected class of variable will be
	  initialized before use in a function.

	config INIT_STACK_NONE
		bool "no automatic stack variable initialization (weakest)"
		help
		  Disable automatic stack variable initialization.
		  This leaves the kernel vulnerable to the standard
		  classes of uninitialized stack variable exploits
		  and information exposures.

	config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
		bool "zero-init everything passed by reference (very strong)"
		depends on GCC_PLUGINS
		select GCC_PLUGIN_STRUCTLEAK
		help
		  Zero-initialize any stack variables that may be passed
		  by reference and had not already been explicitly
		  initialized. This is intended to eliminate all classes
		  of uninitialized stack variable exploits and information
		  exposures.

		  As a side-effect, this keeps a lot of variables on the
		  stack that can otherwise be optimized out, so combining
		  this with CONFIG_KASAN_STACK can lead to a stack overflow
		  and is disallowed.

	config INIT_STACK_ALL_PATTERN
		bool "pattern-init everything (strongest)"
		depends on CC_HAS_AUTO_VAR_INIT_PATTERN
		help
		  Initializes everything on the stack (including padding)
		  with a specific debug value. This is intended to eliminate
		  all classes of uninitialized stack variable exploits and
		  information exposures, even variables that were warned about
		  having been left uninitialized.

		  Pattern initialization is known to provoke many existing bugs
		  related to uninitialized locals, e.g. pointers receive
		  non-NULL values, buffer sizes and indices are very big. The
		  pattern is situation-specific; Clang on 64-bit uses 0xAA
		  repeating for all types and padding except float and double
		  which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
		  repeating for all types and padding.

	config INIT_STACK_ALL_ZERO
		bool "zero-init everything (strongest and safest)"
		depends on CC_HAS_AUTO_VAR_INIT_ZERO
		help
		  Initializes everything on the stack (including padding)
		  with a zero value. This is intended to eliminate all
		  classes of uninitialized stack variable exploits and
		  information exposures, even variables that were warned
		  about having been left uninitialized.

		  Zero initialization provides safe defaults for strings
		  (immediately NUL-terminated), pointers (NULL), indices
		  (index 0), and sizes (0 length), so it is therefore more
		  suitable as a production security mitigation than pattern
		  initialization.

endchoice

config GCC_PLUGIN_STRUCTLEAK_VERBOSE
	bool "Report forcefully initialized variables"
	depends on GCC_PLUGIN_STRUCTLEAK
	depends on !COMPILE_TEST	# too noisy
	help
	  This option will cause a warning to be printed each time the
	  structleak plugin finds a variable it thinks needs to be
	  initialized. Since not all existing initializers are detected
	  by the plugin, this can produce false positive warnings.

config INIT_ON_ALLOC_DEFAULT_ON
	bool "Enable heap memory zeroing on allocation by default"
	help
	  This has the effect of setting "init_on_alloc=1" on the kernel
	  command line. This can be disabled with "init_on_alloc=0".
	  When "init_on_alloc" is enabled, all page allocator and slab
	  allocator memory will be zeroed when allocated, eliminating
	  many kinds of "uninitialized heap memory" flaws, especially
	  heap content exposures. The performance impact varies by
	  workload, but most cases see <1% impact. Some synthetic
	  workloads have measured as high as 7%.

config INIT_ON_FREE_DEFAULT_ON
	bool "Enable heap memory zeroing on free by default"
	help
	  This has the effect of setting "init_on_free=1" on the kernel
	  command line. This can be disabled with "init_on_free=0".
	  Similar to "init_on_alloc", when "init_on_free" is enabled,
	  all page allocator and slab allocator memory will be zeroed
	  when freed, eliminating many kinds of "uninitialized heap memory"
	  flaws, especially heap content exposures. The primary difference
	  with "init_on_free" is that data lifetime in memory is reduced,
	  as anything freed is wiped immediately, making live forensics or
	  cold boot memory attacks unable to recover freed memory contents.
	  The performance impact varies by workload, but is more expensive
	  than "init_on_alloc" due to the negative cache effects of
	  touching "cold" memory areas. Most cases see 3-5% impact. Some
	  synthetic workloads have measured as high as 8%.

endmenu

endmenu