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 select PAGE_POISONING_NO_SANITY if HIBERNATION 68 help 69 Fill the pages with poison patterns after free_pages() and verify 70 the patterns before alloc_pages. The filling of the memory helps 71 reduce the risk of information leaks from freed data. This does 72 have a potential performance impact if enabled with the 73 "page_poison=1" kernel boot option. 74 75 Note that "poison" here is not the same thing as the "HWPoison" 76 for CONFIG_MEMORY_FAILURE. This is software poisoning only. 77 78 If unsure, say N 79 80config PAGE_POISONING_NO_SANITY 81 depends on PAGE_POISONING 82 bool "Only poison, don't sanity check" 83 help 84 Skip the sanity checking on alloc, only fill the pages with 85 poison on free. This reduces some of the overhead of the 86 poisoning feature. 87 88 If you are only interested in sanitization, say Y. Otherwise 89 say N. 90 91config PAGE_POISONING_ZERO 92 bool "Use zero for poisoning instead of debugging value" 93 depends on PAGE_POISONING 94 help 95 Instead of using the existing poison value, fill the pages with 96 zeros. This makes it harder to detect when errors are occurring 97 due to sanitization but the zeroing at free means that it is 98 no longer necessary to write zeros when GFP_ZERO is used on 99 allocation. 100 101 If unsure, say N 102 103config DEBUG_PAGE_REF 104 bool "Enable tracepoint to track down page reference manipulation" 105 depends on DEBUG_KERNEL 106 depends on TRACEPOINTS 107 help 108 This is a feature to add tracepoint for tracking down page reference 109 manipulation. This tracking is useful to diagnose functional failure 110 due to migration failures caused by page reference mismatches. Be 111 careful when enabling this feature because it adds about 30 KB to the 112 kernel code. However the runtime performance overhead is virtually 113 nil until the tracepoints are actually enabled. 114 115config DEBUG_RODATA_TEST 116 bool "Testcase for the marking rodata read-only" 117 depends on STRICT_KERNEL_RWX 118 help 119 This option enables a testcase for the setting rodata read-only. 120 121config ARCH_HAS_DEBUG_WX 122 bool 123 124config DEBUG_WX 125 bool "Warn on W+X mappings at boot" 126 depends on ARCH_HAS_DEBUG_WX 127 depends on MMU 128 select PTDUMP_CORE 129 help 130 Generate a warning if any W+X mappings are found at boot. 131 132 This is useful for discovering cases where the kernel is leaving W+X 133 mappings after applying NX, as such mappings are a security risk. 134 135 Look for a message in dmesg output like this: 136 137 <arch>/mm: Checked W+X mappings: passed, no W+X pages found. 138 139 or like this, if the check failed: 140 141 <arch>/mm: Checked W+X mappings: failed, <N> W+X pages found. 142 143 Note that even if the check fails, your kernel is possibly 144 still fine, as W+X mappings are not a security hole in 145 themselves, what they do is that they make the exploitation 146 of other unfixed kernel bugs easier. 147 148 There is no runtime or memory usage effect of this option 149 once the kernel has booted up - it's a one time check. 150 151 If in doubt, say "Y". 152 153config GENERIC_PTDUMP 154 bool 155 156config PTDUMP_CORE 157 bool 158 159config PTDUMP_DEBUGFS 160 bool "Export kernel pagetable layout to userspace via debugfs" 161 depends on DEBUG_KERNEL 162 depends on DEBUG_FS 163 depends on GENERIC_PTDUMP 164 select PTDUMP_CORE 165 help 166 Say Y here if you want to show the kernel pagetable layout in a 167 debugfs file. This information is only useful for kernel developers 168 who are working in architecture specific areas of the kernel. 169 It is probably not a good idea to enable this feature in a production 170 kernel. 171 172 If in doubt, say N. 173