linux/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 SLUB_DEBUG
	default y
	bool "Enable SLUB debugging support" if EXPERT
	depends on SYSFS && !SLUB_TINY
	select STACKDEPOT if STACKTRACE_SUPPORT
	help
	  SLUB has extensive debug support features. Disabling these can
	  result in significant savings in code size. While /sys/kernel/slab
	  will still exist (with SYSFS enabled), it will not provide e.g. cache
	  validation.

config SLUB_DEBUG_ON
	bool "SLUB debugging on by default"
	depends on SLUB_DEBUG
	select STACKDEPOT_ALWAYS_INIT if STACKTRACE_SUPPORT
	default n
	help
	  Boot with debugging on by default. SLUB boots by default with
	  the runtime debug capabilities switched off. Enabling this is
	  equivalent to specifying the "slab_debug" parameter on boot.
	  There is no support for more fine grained debug control like
	  possible with slab_debug=xxx. SLUB debugging may be switched
	  off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
	  "slab_debug=-".

config SLUB_RCU_DEBUG
	bool "Enable UAF detection in TYPESAFE_BY_RCU caches (for KASAN)"
	depends on SLUB_DEBUG
	# SLUB_RCU_DEBUG should build fine without KASAN, but is currently useless
	# without KASAN, so mark it as a dependency of KASAN for now.
	depends on KASAN
	default KASAN_GENERIC || KASAN_SW_TAGS
	help
	  Make SLAB_TYPESAFE_BY_RCU caches behave approximately as if the cache
	  was not marked as SLAB_TYPESAFE_BY_RCU and every caller used
	  kfree_rcu() instead.

	  This is intended for use in combination with KASAN, to enable KASAN to
	  detect use-after-free accesses in such caches.
	  (KFENCE is able to do that independent of this flag.)

	  This might degrade performance.
	  Unfortunately this also prevents a very specific bug pattern from
	  triggering (insufficient checks against an object being recycled
	  within the RCU grace period); so this option can be turned off even on
	  KASAN builds, in case you want to test for such a bug.

	  If you're using this for testing bugs / fuzzing and care about
	  catching all the bugs WAY more than performance, you might want to
	  also turn on CONFIG_RCU_STRICT_GRACE_PERIOD.

	  WARNING:
	  This is designed as a debugging feature, not a security feature.
	  Objects are sometimes recycled without RCU delay under memory pressure.

	  If unsure, say N.

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/mm/page_owner_sort.c
	  for user-space helper.

	  If unsure, say N.

config PAGE_TABLE_CHECK
	bool "Check for invalid mappings in user page tables"
	depends on ARCH_SUPPORTS_PAGE_TABLE_CHECK
	depends on EXCLUSIVE_SYSTEM_RAM
	select PAGE_EXTENSION
	help
	  Check that anonymous page is not being mapped twice with read write
	  permissions. Check that anonymous and file pages are not being
	  erroneously shared. Since the checking is performed at the time
	  entries are added and removed to user page tables, leaking, corruption
	  and double mapping problems are detected synchronously.

	  If unsure say "n".

config PAGE_TABLE_CHECK_ENFORCED
	bool "Enforce the page table checking by default"
	depends on PAGE_TABLE_CHECK
	help
	  Always enable page table checking.  By default the page table checking
	  is disabled, and can be optionally enabled via page_table_check=on
	  kernel parameter. This config enforces that page table check is always
	  enabled.

	  If unsure say "n".

config PAGE_POISONING
	bool "Poison pages after freeing"
	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 you are only interested in sanitization of freed pages without
	  checking the poison pattern on alloc, you can boot the kernel with
	  "init_on_free=1" instead of enabling this.

	  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.

config HAVE_DEBUG_KMEMLEAK
	bool

config DEBUG_KMEMLEAK
	bool "Kernel memory leak detector"
	depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK
	select DEBUG_FS
	select STACKTRACE if STACKTRACE_SUPPORT
	select KALLSYMS
	select CRC32
	select STACKDEPOT
	select STACKDEPOT_ALWAYS_INIT if !DEBUG_KMEMLEAK_DEFAULT_OFF
	help
	  Say Y here if you want to enable the memory leak
	  detector. The memory allocation/freeing is traced in a way
	  similar to the Boehm's conservative garbage collector, the
	  difference being that the orphan objects are not freed but
	  only shown in /sys/kernel/debug/kmemleak. Enabling this
	  feature will introduce an overhead to memory
	  allocations. See Documentation/dev-tools/kmemleak.rst for more
	  details.

	  Enabling SLUB_DEBUG may increase the chances of finding leaks
	  due to the slab objects poisoning.

	  In order to access the kmemleak file, debugfs needs to be
	  mounted (usually at /sys/kernel/debug).

config DEBUG_KMEMLEAK_MEM_POOL_SIZE
	int "Kmemleak memory pool size"
	depends on DEBUG_KMEMLEAK
	range 200 1000000
	default 16000
	help
	  Kmemleak must track all the memory allocations to avoid
	  reporting false positives. Since memory may be allocated or
	  freed before kmemleak is fully initialised, use a static pool
	  of metadata objects to track such callbacks. After kmemleak is
	  fully initialised, this memory pool acts as an emergency one
	  if slab allocations fail.

config DEBUG_KMEMLEAK_DEFAULT_OFF
	bool "Default kmemleak to off"
	depends on DEBUG_KMEMLEAK
	help
	  Say Y here to disable kmemleak by default. It can then be enabled
	  on the command line via kmemleak=on.

config DEBUG_KMEMLEAK_AUTO_SCAN
	bool "Enable kmemleak auto scan thread on boot up"
	default y
	depends on DEBUG_KMEMLEAK
	help
	  Depending on the cpu, kmemleak scan may be cpu intensive and can
	  stall user tasks at times. This option enables/disables automatic
	  kmemleak scan at boot up.

	  Say N here to disable kmemleak auto scan thread to stop automatic
	  scanning. Disabling this option disables automatic reporting of
	  memory leaks.

	  If unsure, say Y.

config PER_VMA_LOCK_STATS
	bool "Statistics for per-vma locks"
	depends on PER_VMA_LOCK
	help
	  Say Y here to enable success, retry and failure counters of page
	  faults handled under protection of per-vma locks. When enabled, the
	  counters are exposed in /proc/vmstat. This information is useful for
	  kernel developers to evaluate effectiveness of per-vma locks and to
	  identify pathological cases. Counting these events introduces a small
	  overhead in the page fault path.

	  If in doubt, say N.