# SPDX-License-Identifier: GPL-2.0-only
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menu "Kernel hardening options"
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config GCC_PLUGIN_STRUCTLEAK
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bool
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help
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While the kernel is built with warnings enabled for any missed
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stack variable initializations, this warning is silenced for
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anything passed by reference to another function, under the
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occasionally misguided assumption that the function will do
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the initialization. As this regularly leads to exploitable
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flaws, this plugin is available to identify and zero-initialize
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such variables, depending on the chosen level of coverage.
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This plugin was originally ported from grsecurity/PaX. More
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information at:
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* https://grsecurity.net/
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* https://pax.grsecurity.net/
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menu "Memory initialization"
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config CC_HAS_AUTO_VAR_INIT_PATTERN
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def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
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config CC_HAS_AUTO_VAR_INIT_ZERO_BARE
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def_bool $(cc-option,-ftrivial-auto-var-init=zero)
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config CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER
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# Clang 16 and later warn about using the -enable flag, but it
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# is required before then.
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def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)
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depends on !CC_HAS_AUTO_VAR_INIT_ZERO_BARE
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config CC_HAS_AUTO_VAR_INIT_ZERO
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def_bool CC_HAS_AUTO_VAR_INIT_ZERO_BARE || CC_HAS_AUTO_VAR_INIT_ZERO_ENABLER
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choice
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prompt "Initialize kernel stack variables at function entry"
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default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
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default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
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default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
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default INIT_STACK_NONE
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help
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This option enables initialization of stack variables at
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function entry time. This has the possibility to have the
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greatest coverage (since all functions can have their
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variables initialized), but the performance impact depends
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on the function calling complexity of a given workload's
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syscalls.
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This chooses the level of coverage over classes of potentially
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uninitialized variables. The selected class of variable will be
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initialized before use in a function.
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config INIT_STACK_NONE
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bool "no automatic stack variable initialization (weakest)"
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help
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Disable automatic stack variable initialization.
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This leaves the kernel vulnerable to the standard
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classes of uninitialized stack variable exploits
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and information exposures.
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config GCC_PLUGIN_STRUCTLEAK_USER
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bool "zero-init structs marked for userspace (weak)"
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depends on GCC_PLUGINS
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select GCC_PLUGIN_STRUCTLEAK
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help
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Zero-initialize any structures on the stack containing
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a __user attribute. This can prevent some classes of
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uninitialized stack variable exploits and information
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exposures, like CVE-2013-2141:
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https://git.kernel.org/linus/b9e146d8eb3b9eca
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config GCC_PLUGIN_STRUCTLEAK_BYREF
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bool "zero-init structs passed by reference (strong)"
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depends on GCC_PLUGINS
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depends on !(KASAN && KASAN_STACK)
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select GCC_PLUGIN_STRUCTLEAK
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help
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Zero-initialize any structures on the stack that may
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be passed by reference and had not already been
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explicitly initialized. This can prevent most classes
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of uninitialized stack variable exploits and information
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exposures, like CVE-2017-1000410:
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https://git.kernel.org/linus/06e7e776ca4d3654
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As a side-effect, this keeps a lot of variables on the
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stack that can otherwise be optimized out, so combining
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this with CONFIG_KASAN_STACK can lead to a stack overflow
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and is disallowed.
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config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
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bool "zero-init everything passed by reference (very strong)"
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depends on GCC_PLUGINS
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depends on !(KASAN && KASAN_STACK)
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select GCC_PLUGIN_STRUCTLEAK
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help
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Zero-initialize any stack variables that may be passed
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by reference and had not already been explicitly
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initialized. This is intended to eliminate all classes
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of uninitialized stack variable exploits and information
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exposures.
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As a side-effect, this keeps a lot of variables on the
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stack that can otherwise be optimized out, so combining
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this with CONFIG_KASAN_STACK can lead to a stack overflow
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and is disallowed.
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config INIT_STACK_ALL_PATTERN
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bool "pattern-init everything (strongest)"
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depends on CC_HAS_AUTO_VAR_INIT_PATTERN
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help
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Initializes everything on the stack (including padding)
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with a specific debug value. This is intended to eliminate
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all classes of uninitialized stack variable exploits and
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information exposures, even variables that were warned about
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having been left uninitialized.
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Pattern initialization is known to provoke many existing bugs
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related to uninitialized locals, e.g. pointers receive
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non-NULL values, buffer sizes and indices are very big. The
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pattern is situation-specific; Clang on 64-bit uses 0xAA
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repeating for all types and padding except float and double
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which use 0xFF repeating (-NaN). Clang on 32-bit uses 0xFF
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repeating for all types and padding.
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config INIT_STACK_ALL_ZERO
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bool "zero-init everything (strongest and safest)"
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depends on CC_HAS_AUTO_VAR_INIT_ZERO
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help
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Initializes everything on the stack (including padding)
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with a zero value. This is intended to eliminate all
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classes of uninitialized stack variable exploits and
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information exposures, even variables that were warned
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about having been left uninitialized.
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Zero initialization provides safe defaults for strings
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(immediately NUL-terminated), pointers (NULL), indices
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(index 0), and sizes (0 length), so it is therefore more
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suitable as a production security mitigation than pattern
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initialization.
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endchoice
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config GCC_PLUGIN_STRUCTLEAK_VERBOSE
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bool "Report forcefully initialized variables"
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depends on GCC_PLUGIN_STRUCTLEAK
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depends on !COMPILE_TEST # too noisy
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help
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This option will cause a warning to be printed each time the
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structleak plugin finds a variable it thinks needs to be
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initialized. Since not all existing initializers are detected
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by the plugin, this can produce false positive warnings.
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config GCC_PLUGIN_STACKLEAK
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bool "Poison kernel stack before returning from syscalls"
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depends on GCC_PLUGINS
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depends on HAVE_ARCH_STACKLEAK
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help
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This option makes the kernel erase the kernel stack before
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returning from system calls. This has the effect of leaving
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the stack initialized to the poison value, which both reduces
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the lifetime of any sensitive stack contents and reduces
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potential for uninitialized stack variable exploits or information
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exposures (it does not cover functions reaching the same stack
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depth as prior functions during the same syscall). This blocks
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most uninitialized stack variable attacks, with the performance
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impact being driven by the depth of the stack usage, rather than
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the function calling complexity.
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The performance impact on a single CPU system kernel compilation
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sees a 1% slowdown, other systems and workloads may vary and you
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are advised to test this feature on your expected workload before
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deploying it.
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This plugin was ported from grsecurity/PaX. More information at:
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* https://grsecurity.net/
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* https://pax.grsecurity.net/
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config STACKLEAK_TRACK_MIN_SIZE
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int "Minimum stack frame size of functions tracked by STACKLEAK"
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default 100
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range 0 4096
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depends on GCC_PLUGIN_STACKLEAK
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help
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The STACKLEAK gcc plugin instruments the kernel code for tracking
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the lowest border of the kernel stack (and for some other purposes).
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It inserts the stackleak_track_stack() call for the functions with
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a stack frame size greater than or equal to this parameter.
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If unsure, leave the default value 100.
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config STACKLEAK_METRICS
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bool "Show STACKLEAK metrics in the /proc file system"
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depends on GCC_PLUGIN_STACKLEAK
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depends on PROC_FS
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help
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If this is set, STACKLEAK metrics for every task are available in
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the /proc file system. In particular, /proc/<pid>/stack_depth
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shows the maximum kernel stack consumption for the current and
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previous syscalls. Although this information is not precise, it
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can be useful for estimating the STACKLEAK performance impact for
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your workloads.
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config STACKLEAK_RUNTIME_DISABLE
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bool "Allow runtime disabling of kernel stack erasing"
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depends on GCC_PLUGIN_STACKLEAK
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help
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This option provides 'stack_erasing' sysctl, which can be used in
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runtime to control kernel stack erasing for kernels built with
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CONFIG_GCC_PLUGIN_STACKLEAK.
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config INIT_ON_ALLOC_DEFAULT_ON
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bool "Enable heap memory zeroing on allocation by default"
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help
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This has the effect of setting "init_on_alloc=1" on the kernel
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command line. This can be disabled with "init_on_alloc=0".
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When "init_on_alloc" is enabled, all page allocator and slab
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allocator memory will be zeroed when allocated, eliminating
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many kinds of "uninitialized heap memory" flaws, especially
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heap content exposures. The performance impact varies by
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workload, but most cases see <1% impact. Some synthetic
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workloads have measured as high as 7%.
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config INIT_ON_FREE_DEFAULT_ON
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bool "Enable heap memory zeroing on free by default"
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help
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This has the effect of setting "init_on_free=1" on the kernel
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command line. This can be disabled with "init_on_free=0".
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Similar to "init_on_alloc", when "init_on_free" is enabled,
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all page allocator and slab allocator memory will be zeroed
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when freed, eliminating many kinds of "uninitialized heap memory"
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flaws, especially heap content exposures. The primary difference
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with "init_on_free" is that data lifetime in memory is reduced,
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as anything freed is wiped immediately, making live forensics or
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cold boot memory attacks unable to recover freed memory contents.
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The performance impact varies by workload, but is more expensive
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than "init_on_alloc" due to the negative cache effects of
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touching "cold" memory areas. Most cases see 3-5% impact. Some
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synthetic workloads have measured as high as 8%.
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endmenu
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endmenu
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