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Check user page table entries at the time they are added and removed. Allows to synchronously catch memory corruption issues related to double mapping. When a pte for an anonymous page is added into page table, we verify that this pte does not already point to a file backed page, and vice versa if this is a file backed page that is being added we verify that this page does not have an anonymous mapping We also enforce that read-only sharing for anonymous pages is allowed (i.e. cow after fork). All other sharing must be for file pages. Page table check allows to protect and debug cases where "struct page" metadata became corrupted for some reason. For example, when refcnt or mapcount become invalid. Link: https://lkml.kernel.org/r/20211221154650.1047963-4-pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Rientjes <rientjes@google.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Greg Thelen <gthelen@google.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Hugh Dickins <hughd@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jiri Slaby <jirislaby@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kees Cook <keescook@chromium.org> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Mike Rapoport <rppt@kernel.org> Cc: Muchun Song <songmuchun@bytedance.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sami Tolvanen <samitolvanen@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Wei Xu <weixugc@google.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
177 lines
6.4 KiB
Plaintext
177 lines
6.4 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config PAGE_EXTENSION
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bool "Extend memmap on extra space for more information on page"
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help
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Extend memmap on extra space for more information on page. This
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could be used for debugging features that need to insert extra
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field for every page. This extension enables us to save memory
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by not allocating this extra memory according to boottime
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configuration.
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config DEBUG_PAGEALLOC
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bool "Debug page memory allocations"
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depends on DEBUG_KERNEL
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depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
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select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
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help
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Unmap pages from the kernel linear mapping after free_pages().
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Depending on runtime enablement, this results in a small or large
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slowdown, but helps to find certain types of memory corruption.
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Also, the state of page tracking structures is checked more often as
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pages are being allocated and freed, as unexpected state changes
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often happen for same reasons as memory corruption (e.g. double free,
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use-after-free). The error reports for these checks can be augmented
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with stack traces of last allocation and freeing of the page, when
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PAGE_OWNER is also selected and enabled on boot.
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For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
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fill the pages with poison patterns after free_pages() and verify
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the patterns before alloc_pages(). Additionally, this option cannot
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be enabled in combination with hibernation as that would result in
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incorrect warnings of memory corruption after a resume because free
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pages are not saved to the suspend image.
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By default this option will have a small overhead, e.g. by not
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allowing the kernel mapping to be backed by large pages on some
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architectures. Even bigger overhead comes when the debugging is
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enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
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command line parameter.
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config DEBUG_PAGEALLOC_ENABLE_DEFAULT
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bool "Enable debug page memory allocations by default?"
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depends on DEBUG_PAGEALLOC
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help
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Enable debug page memory allocations by default? This value
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can be overridden by debug_pagealloc=off|on.
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config PAGE_OWNER
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bool "Track page owner"
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depends on DEBUG_KERNEL && STACKTRACE_SUPPORT
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select DEBUG_FS
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select STACKTRACE
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select STACKDEPOT
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select PAGE_EXTENSION
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help
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This keeps track of what call chain is the owner of a page, may
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help to find bare alloc_page(s) leaks. Even if you include this
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feature on your build, it is disabled in default. You should pass
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"page_owner=on" to boot parameter in order to enable it. Eats
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a fair amount of memory if enabled. See tools/vm/page_owner_sort.c
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for user-space helper.
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If unsure, say N.
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config PAGE_TABLE_CHECK
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bool "Check for invalid mappings in user page tables"
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depends on ARCH_SUPPORTS_PAGE_TABLE_CHECK
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select PAGE_EXTENSION
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help
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Check that anonymous page is not being mapped twice with read write
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permissions. Check that anonymous and file pages are not being
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erroneously shared. Since the checking is performed at the time
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entries are added and removed to user page tables, leaking, corruption
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and double mapping problems are detected synchronously.
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If unsure say "n".
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config PAGE_TABLE_CHECK_ENFORCED
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bool "Enforce the page table checking by default"
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depends on PAGE_TABLE_CHECK
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help
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Always enable page table checking. By default the page table checking
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is disabled, and can be optionally enabled via page_table_check=on
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kernel parameter. This config enforces that page table check is always
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enabled.
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If unsure say "n".
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config PAGE_POISONING
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bool "Poison pages after freeing"
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help
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Fill the pages with poison patterns after free_pages() and verify
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the patterns before alloc_pages. The filling of the memory helps
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reduce the risk of information leaks from freed data. This does
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have a potential performance impact if enabled with the
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"page_poison=1" kernel boot option.
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Note that "poison" here is not the same thing as the "HWPoison"
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for CONFIG_MEMORY_FAILURE. This is software poisoning only.
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If you are only interested in sanitization of freed pages without
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checking the poison pattern on alloc, you can boot the kernel with
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"init_on_free=1" instead of enabling this.
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If unsure, say N
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config DEBUG_PAGE_REF
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bool "Enable tracepoint to track down page reference manipulation"
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depends on DEBUG_KERNEL
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depends on TRACEPOINTS
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help
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This is a feature to add tracepoint for tracking down page reference
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manipulation. This tracking is useful to diagnose functional failure
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due to migration failures caused by page reference mismatches. Be
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careful when enabling this feature because it adds about 30 KB to the
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kernel code. However the runtime performance overhead is virtually
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nil until the tracepoints are actually enabled.
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config DEBUG_RODATA_TEST
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bool "Testcase for the marking rodata read-only"
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depends on STRICT_KERNEL_RWX
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help
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This option enables a testcase for the setting rodata read-only.
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config ARCH_HAS_DEBUG_WX
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bool
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config DEBUG_WX
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bool "Warn on W+X mappings at boot"
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depends on ARCH_HAS_DEBUG_WX
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depends on MMU
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select PTDUMP_CORE
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help
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Generate a warning if any W+X mappings are found at boot.
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This is useful for discovering cases where the kernel is leaving W+X
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mappings after applying NX, as such mappings are a security risk.
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Look for a message in dmesg output like this:
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<arch>/mm: Checked W+X mappings: passed, no W+X pages found.
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or like this, if the check failed:
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<arch>/mm: Checked W+X mappings: failed, <N> W+X pages found.
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Note that even if the check fails, your kernel is possibly
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still fine, as W+X mappings are not a security hole in
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themselves, what they do is that they make the exploitation
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of other unfixed kernel bugs easier.
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There is no runtime or memory usage effect of this option
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once the kernel has booted up - it's a one time check.
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If in doubt, say "Y".
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config GENERIC_PTDUMP
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bool
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config PTDUMP_CORE
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bool
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config PTDUMP_DEBUGFS
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bool "Export kernel pagetable layout to userspace via debugfs"
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depends on DEBUG_KERNEL
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depends on DEBUG_FS
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depends on GENERIC_PTDUMP
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select PTDUMP_CORE
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help
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Say Y here if you want to show the kernel pagetable layout in a
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debugfs file. This information is only useful for kernel developers
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who are working in architecture specific areas of the kernel.
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It is probably not a good idea to enable this feature in a production
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kernel.
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If in doubt, say N.
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