1# SPDX-License-Identifier: GPL-2.0-only
2config PAGE_EXTENSION
3	bool "Extend memmap on extra space for more information on page"
4	help
5	  Extend memmap on extra space for more information on page. This
6	  could be used for debugging features that need to insert extra
7	  field for every page. This extension enables us to save memory
8	  by not allocating this extra memory according to boottime
9	  configuration.
10
11config DEBUG_PAGEALLOC
12	bool "Debug page memory allocations"
13	depends on DEBUG_KERNEL
14	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
15	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
16	help
17	  Unmap pages from the kernel linear mapping after free_pages().
18	  Depending on runtime enablement, this results in a small or large
19	  slowdown, but helps to find certain types of memory corruption.
20
21	  Also, the state of page tracking structures is checked more often as
22	  pages are being allocated and freed, as unexpected state changes
23	  often happen for same reasons as memory corruption (e.g. double free,
24	  use-after-free). The error reports for these checks can be augmented
25	  with stack traces of last allocation and freeing of the page, when
26	  PAGE_OWNER is also selected and enabled on boot.
27
28	  For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
29	  fill the pages with poison patterns after free_pages() and verify
30	  the patterns before alloc_pages(). Additionally, this option cannot
31	  be enabled in combination with hibernation as that would result in
32	  incorrect warnings of memory corruption after a resume because free
33	  pages are not saved to the suspend image.
34
35	  By default this option will have a small overhead, e.g. by not
36	  allowing the kernel mapping to be backed by large pages on some
37	  architectures. Even bigger overhead comes when the debugging is
38	  enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
39	  command line parameter.
40
41config DEBUG_PAGEALLOC_ENABLE_DEFAULT
42	bool "Enable debug page memory allocations by default?"
43	depends on DEBUG_PAGEALLOC
44	help
45	  Enable debug page memory allocations by default? This value
46	  can be overridden by debug_pagealloc=off|on.
47
48config PAGE_OWNER
49	bool "Track page owner"
50	depends on DEBUG_KERNEL && STACKTRACE_SUPPORT
51	select DEBUG_FS
52	select STACKTRACE
53	select STACKDEPOT
54	select PAGE_EXTENSION
55	help
56	  This keeps track of what call chain is the owner of a page, may
57	  help to find bare alloc_page(s) leaks. Even if you include this
58	  feature on your build, it is disabled in default. You should pass
59	  "page_owner=on" to boot parameter in order to enable it. Eats
60	  a fair amount of memory if enabled. See tools/vm/page_owner_sort.c
61	  for user-space helper.
62
63	  If unsure, say N.
64
65config PAGE_POISONING
66	bool "Poison pages after freeing"
67	help
68	  Fill the pages with poison patterns after free_pages() and verify
69	  the patterns before alloc_pages. The filling of the memory helps
70	  reduce the risk of information leaks from freed data. This does
71	  have a potential performance impact if enabled with the
72	  "page_poison=1" kernel boot option.
73
74	  Note that "poison" here is not the same thing as the "HWPoison"
75	  for CONFIG_MEMORY_FAILURE. This is software poisoning only.
76
77	  If you are only interested in sanitization of freed pages without
78	  checking the poison pattern on alloc, you can boot the kernel with
79	  "init_on_free=1" instead of enabling this.
80
81	  If unsure, say N
82
83config DEBUG_PAGE_REF
84	bool "Enable tracepoint to track down page reference manipulation"
85	depends on DEBUG_KERNEL
86	depends on TRACEPOINTS
87	help
88	  This is a feature to add tracepoint for tracking down page reference
89	  manipulation. This tracking is useful to diagnose functional failure
90	  due to migration failures caused by page reference mismatches.  Be
91	  careful when enabling this feature because it adds about 30 KB to the
92	  kernel code.  However the runtime performance overhead is virtually
93	  nil until the tracepoints are actually enabled.
94
95config DEBUG_RODATA_TEST
96    bool "Testcase for the marking rodata read-only"
97    depends on STRICT_KERNEL_RWX
98	help
99      This option enables a testcase for the setting rodata read-only.
100
101config ARCH_HAS_DEBUG_WX
102	bool
103
104config DEBUG_WX
105	bool "Warn on W+X mappings at boot"
106	depends on ARCH_HAS_DEBUG_WX
107	depends on MMU
108	select PTDUMP_CORE
109	help
110	  Generate a warning if any W+X mappings are found at boot.
111
112	  This is useful for discovering cases where the kernel is leaving W+X
113	  mappings after applying NX, as such mappings are a security risk.
114
115	  Look for a message in dmesg output like this:
116
117	    <arch>/mm: Checked W+X mappings: passed, no W+X pages found.
118
119	  or like this, if the check failed:
120
121	    <arch>/mm: Checked W+X mappings: failed, <N> W+X pages found.
122
123	  Note that even if the check fails, your kernel is possibly
124	  still fine, as W+X mappings are not a security hole in
125	  themselves, what they do is that they make the exploitation
126	  of other unfixed kernel bugs easier.
127
128	  There is no runtime or memory usage effect of this option
129	  once the kernel has booted up - it's a one time check.
130
131	  If in doubt, say "Y".
132
133config GENERIC_PTDUMP
134	bool
135
136config PTDUMP_CORE
137	bool
138
139config PTDUMP_DEBUGFS
140	bool "Export kernel pagetable layout to userspace via debugfs"
141	depends on DEBUG_KERNEL
142	depends on DEBUG_FS
143	depends on GENERIC_PTDUMP
144	select PTDUMP_CORE
145	help
146	  Say Y here if you want to show the kernel pagetable layout in a
147	  debugfs file. This information is only useful for kernel developers
148	  who are working in architecture specific areas of the kernel.
149	  It is probably not a good idea to enable this feature in a production
150	  kernel.
151
152	  If in doubt, say N.
153