# 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" 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.