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# 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 DEBUG_SLAB
bool "Debug slab memory allocations"
depends on DEBUG_KERNEL && SLAB
help
Say Y here to have the kernel do limited verification on memory
allocation as well as poisoning memory on free to catch use of freed
memory. This can make kmalloc/kfree-intensive workloads much slower.
config SLUB_DEBUG
default y
bool "Enable SLUB debugging support" if EXPERT
depends on SLUB && SYSFS
select STACKDEPOT if STACKTRACE_SUPPORT
help
SLUB has extensive debug support features. Disabling these can
result in significant savings in code size. This also disables
SLUB sysfs support. /sys/slab will not exist and there will be
no support for cache validation etc.
config SLUB_DEBUG_ON
bool "SLUB debugging on by default"
depends on SLUB && 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 "slub_debug" parameter on boot.
There is no support for more fine grained debug control like
possible with slub_debug=xxx. SLUB debugging may be switched
off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
"slub_debug=-".
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_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.
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