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_TABLE_CHECK 66 bool "Check for invalid mappings in user page tables" 67 depends on ARCH_SUPPORTS_PAGE_TABLE_CHECK 68 select PAGE_EXTENSION 69 help 70 Check that anonymous page is not being mapped twice with read write 71 permissions. Check that anonymous and file pages are not being 72 erroneously shared. Since the checking is performed at the time 73 entries are added and removed to user page tables, leaking, corruption 74 and double mapping problems are detected synchronously. 75 76 If unsure say "n". 77 78config PAGE_TABLE_CHECK_ENFORCED 79 bool "Enforce the page table checking by default" 80 depends on PAGE_TABLE_CHECK 81 help 82 Always enable page table checking. By default the page table checking 83 is disabled, and can be optionally enabled via page_table_check=on 84 kernel parameter. This config enforces that page table check is always 85 enabled. 86 87 If unsure say "n". 88 89config PAGE_POISONING 90 bool "Poison pages after freeing" 91 help 92 Fill the pages with poison patterns after free_pages() and verify 93 the patterns before alloc_pages. The filling of the memory helps 94 reduce the risk of information leaks from freed data. This does 95 have a potential performance impact if enabled with the 96 "page_poison=1" kernel boot option. 97 98 Note that "poison" here is not the same thing as the "HWPoison" 99 for CONFIG_MEMORY_FAILURE. This is software poisoning only. 100 101 If you are only interested in sanitization of freed pages without 102 checking the poison pattern on alloc, you can boot the kernel with 103 "init_on_free=1" instead of enabling this. 104 105 If unsure, say N 106 107config DEBUG_PAGE_REF 108 bool "Enable tracepoint to track down page reference manipulation" 109 depends on DEBUG_KERNEL 110 depends on TRACEPOINTS 111 help 112 This is a feature to add tracepoint for tracking down page reference 113 manipulation. This tracking is useful to diagnose functional failure 114 due to migration failures caused by page reference mismatches. Be 115 careful when enabling this feature because it adds about 30 KB to the 116 kernel code. However the runtime performance overhead is virtually 117 nil until the tracepoints are actually enabled. 118 119config DEBUG_RODATA_TEST 120 bool "Testcase for the marking rodata read-only" 121 depends on STRICT_KERNEL_RWX 122 help 123 This option enables a testcase for the setting rodata read-only. 124 125config ARCH_HAS_DEBUG_WX 126 bool 127 128config DEBUG_WX 129 bool "Warn on W+X mappings at boot" 130 depends on ARCH_HAS_DEBUG_WX 131 depends on MMU 132 select PTDUMP_CORE 133 help 134 Generate a warning if any W+X mappings are found at boot. 135 136 This is useful for discovering cases where the kernel is leaving W+X 137 mappings after applying NX, as such mappings are a security risk. 138 139 Look for a message in dmesg output like this: 140 141 <arch>/mm: Checked W+X mappings: passed, no W+X pages found. 142 143 or like this, if the check failed: 144 145 <arch>/mm: Checked W+X mappings: failed, <N> W+X pages found. 146 147 Note that even if the check fails, your kernel is possibly 148 still fine, as W+X mappings are not a security hole in 149 themselves, what they do is that they make the exploitation 150 of other unfixed kernel bugs easier. 151 152 There is no runtime or memory usage effect of this option 153 once the kernel has booted up - it's a one time check. 154 155 If in doubt, say "Y". 156 157config GENERIC_PTDUMP 158 bool 159 160config PTDUMP_CORE 161 bool 162 163config PTDUMP_DEBUGFS 164 bool "Export kernel pagetable layout to userspace via debugfs" 165 depends on DEBUG_KERNEL 166 depends on DEBUG_FS 167 depends on GENERIC_PTDUMP 168 select PTDUMP_CORE 169 help 170 Say Y here if you want to show the kernel pagetable layout in a 171 debugfs file. This information is only useful for kernel developers 172 who are working in architecture specific areas of the kernel. 173 It is probably not a good idea to enable this feature in a production 174 kernel. 175 176 If in doubt, say N. 177