mm/Kconfig.debug

# SPDX-License-Identifier: GPL-2.0-only
config PAGE_EXTENSION
	bool "Extend memmap on extra space for more information on page"
	help
	  Extend memmap on extra space for more information on page. This
	  could be used for debugging features that need to insert extra
	  field for every page. This extension enables us to save memory
	  by not allocating this extra memory according to boottime
	  configuration.

config DEBUG_PAGEALLOC
	bool "Debug page memory allocations"
	depends on DEBUG_KERNEL
	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
	help
	  Unmap pages from the kernel linear mapping after free_pages().
	  Depending on runtime enablement, this results in a small or large
	  slowdown, but helps to find certain types of memory corruption.

	  Also, the state of page tracking structures is checked more often as
	  pages are being allocated and freed, as unexpected state changes
	  often happen for same reasons as memory corruption (e.g. double free,
	  use-after-free). The error reports for these checks can be augmented
	  with stack traces of last allocation and freeing of the page, when
	  PAGE_OWNER is also selected and enabled on boot.

	  For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
	  fill the pages with poison patterns after free_pages() and verify
	  the patterns before alloc_pages(). Additionally, this option cannot
	  be enabled in combination with hibernation as that would result in
	  incorrect warnings of memory corruption after a resume because free
	  pages are not saved to the suspend image.

	  By default this option will have a small overhead, e.g. by not
	  allowing the kernel mapping to be backed by large pages on some
	  architectures. Even bigger overhead comes when the debugging is
	  enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
	  command line parameter.

config DEBUG_PAGEALLOC_ENABLE_DEFAULT
	bool "Enable debug page memory allocations by default?"
	depends on DEBUG_PAGEALLOC
	help
	  Enable debug page memory allocations by default? This value
	  can be overridden by debug_pagealloc=off|on.

config PAGE_OWNER
	bool "Track page owner"
	depends on DEBUG_KERNEL && STACKTRACE_SUPPORT
	select DEBUG_FS
	select STACKTRACE
	select STACKDEPOT
	select PAGE_EXTENSION
	help
	  This keeps track of what call chain is the owner of a page, may
	  help to find bare alloc_page(s) leaks. Even if you include this
	  feature on your build, it is disabled in default. You should pass
	  "page_owner=on" to boot parameter in order to enable it. Eats
	  a fair amount of memory if enabled. See tools/vm/page_owner_sort.c
	  for user-space helper.

	  If unsure, say N.

config PAGE_POISONING
	bool "Poison pages after freeing"
	select PAGE_POISONING_NO_SANITY if HIBERNATION
	help
	  Fill the pages with poison patterns after free_pages() and verify
	  the patterns before alloc_pages. The filling of the memory helps
	  reduce the risk of information leaks from freed data. This does
	  have a potential performance impact if enabled with the
	  "page_poison=1" kernel boot option.

	  Note that "poison" here is not the same thing as the "HWPoison"
	  for CONFIG_MEMORY_FAILURE. This is software poisoning only.

	  If unsure, say N

config PAGE_POISONING_NO_SANITY
	depends on PAGE_POISONING
	bool "Only poison, don't sanity check"
	help
	   Skip the sanity checking on alloc, only fill the pages with
	   poison on free. This reduces some of the overhead of the
	   poisoning feature.

	   If you are only interested in sanitization, say Y. Otherwise
	   say N.

config PAGE_POISONING_ZERO
	bool "Use zero for poisoning instead of debugging value"
	depends on PAGE_POISONING
	help
	   Instead of using the existing poison value, fill the pages with
	   zeros. This makes it harder to detect when errors are occurring
	   due to sanitization but the zeroing at free means that it is
	   no longer necessary to write zeros when GFP_ZERO is used on
	   allocation.

	   If unsure, say N

config DEBUG_PAGE_REF
	bool "Enable tracepoint to track down page reference manipulation"
	depends on DEBUG_KERNEL
	depends on TRACEPOINTS
	help
	  This is a feature to add tracepoint for tracking down page reference
	  manipulation. This tracking is useful to diagnose functional failure
	  due to migration failures caused by page reference mismatches.  Be
	  careful when enabling this feature because it adds about 30 KB to the
	  kernel code.  However the runtime performance overhead is virtually
	  nil until the tracepoints are actually enabled.

config DEBUG_RODATA_TEST
    bool "Testcase for the marking rodata read-only"
    depends on STRICT_KERNEL_RWX
	help
      This option enables a testcase for the setting rodata read-only.

config ARCH_HAS_DEBUG_WX
	bool

config DEBUG_WX
	bool "Warn on W+X mappings at boot"
	depends on ARCH_HAS_DEBUG_WX
	depends on MMU
	select PTDUMP_CORE
	help
	  Generate a warning if any W+X mappings are found at boot.

	  This is useful for discovering cases where the kernel is leaving W+X
	  mappings after applying NX, as such mappings are a security risk.

	  Look for a message in dmesg output like this:

	    <arch>/mm: Checked W+X mappings: passed, no W+X pages found.

	  or like this, if the check failed:

	    <arch>/mm: Checked W+X mappings: failed, <N> W+X pages found.

	  Note that even if the check fails, your kernel is possibly
	  still fine, as W+X mappings are not a security hole in
	  themselves, what they do is that they make the exploitation
	  of other unfixed kernel bugs easier.

	  There is no runtime or memory usage effect of this option
	  once the kernel has booted up - it's a one time check.

	  If in doubt, say "Y".

config GENERIC_PTDUMP
	bool

config PTDUMP_CORE
	bool

config PTDUMP_DEBUGFS
	bool "Export kernel pagetable layout to userspace via debugfs"
	depends on DEBUG_KERNEL
	depends on DEBUG_FS
	depends on GENERIC_PTDUMP
	select PTDUMP_CORE
	help
	  Say Y here if you want to show the kernel pagetable layout in a
	  debugfs file. This information is only useful for kernel developers
	  who are working in architecture specific areas of the kernel.
	  It is probably not a good idea to enable this feature in a production
	  kernel.

	  If in doubt, say N.