[PATCH v2] arch, mm: promote DEBUG_WX to CHECK_WX
Anshuman Khandual
anshuman.khandual at arm.com
Sun Sep 27 22:54:40 PDT 2026
On Sat, Sep 26, 2026 at 12:29:29PM +0300, Mike Rapoport (Microsoft) wrote:
> Verification that the kernel does not have writable + executable
> mappings is about detecting security risks rather than a pure debug
> feature.
>
> Major distribution configurations enable it in their kernels as well as
> defconfigs of most architectures that have ARCH_HAS_DEBUG_WX.
>
> Rename relevant generic configuration options to use CHECK_WX and move
> their definitions from mm/Kconfig.debug to mm/Kconfig.
>
> Rename *debug_checkwx() funcitons and macros to *pgtable_checkwx().
A small nit - pgtable_ckeck_wx() might be better and also consistent with
renamed config CHECK_WX ?
>
> For arm that does not widely enable it, only rename its variants of the
> config options.
>
> Enabling CHECK_WX adds a few kilobytes to the kernel binary and while
> the added size can be slightly reduced with churny updates of
> architecture implementations of ptdump, the core functionality takes
> most of the added size. It cannot be moved to .init.text because the
> verification has to happen after init sections are freed.
>
> With this, make generic CHECK_WX default to STRICT_KERNEL_RWX while
> still leaving users targeting small kernels the possibility to opt-out.
Although the commit message clearly spells out "promote" DEBUG_WX but still
wondering would it be better to split this change into two patches instead.
- Rename DEBUG_WX as CHECK_WX including all depenencies and helpers
- Change CHECK_WX behaviour like defaulting with STRICT_KERNEL_RWX which
was not the case earlier
>
> Suggested-by: Dave Hansen <dave.hansen at linux.intel.com>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt at kernel.org>
> ---
> Changes in v2:
> - add rename of *debug_checkwx() to *pgtable_checkwx()
> - Link to v1: https://patch.msgid.link/20260925-direct-map-verify-wx-v1-1-7fd2f7d6d23b@kernel.org
> ---
> arch/arm/Kconfig.debug | 2 +-
> arch/arm/configs/aspeed_g4_defconfig | 2 +-
> arch/arm/configs/aspeed_g5_defconfig | 2 +-
> arch/arm/configs/shmobile_defconfig | 2 +-
> arch/arm/include/asm/ptdump.h | 6 +++---
> arch/arm/mm/init.c | 2 +-
> arch/arm64/Kconfig | 2 +-
> arch/powerpc/Kconfig | 2 +-
> arch/powerpc/configs/ppc64_defconfig | 2 +-
> arch/powerpc/mm/ptdump/ptdump.c | 2 +-
> arch/riscv/Kconfig | 2 +-
> arch/s390/Kconfig | 2 +-
> arch/s390/configs/debug_defconfig | 2 +-
> arch/s390/configs/defconfig | 2 +-
> arch/s390/mm/dump_pagetables.c | 2 +-
> arch/x86/Kconfig | 2 +-
> arch/x86/configs/x86_64_defconfig | 2 +-
> arch/x86/include/asm/pgtable.h | 6 +++---
> arch/x86/mm/pti.c | 2 +-
> include/linux/ptdump.h | 4 ++--
> init/main.c | 2 +-
> kernel/configs/debug.config | 2 +-
> mm/Kconfig | 41 ++++++++++++++++++++++++++++++++++++
> mm/Kconfig.debug | 39 ----------------------------------
> 24 files changed, 68 insertions(+), 66 deletions(-)
>
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 366f162e147d..abcf14f10276 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -17,7 +17,7 @@ config ARM_PTDUMP_DEBUGFS
> kernel.
> If in doubt, say "N"
>
> -config ARM_DEBUG_WX
> +config ARM_CHECK_WX
> bool "Warn on W+X mappings at boot"
> depends on MMU
> select ARM_PTDUMP_CORE
> diff --git a/arch/arm/configs/aspeed_g4_defconfig b/arch/arm/configs/aspeed_g4_defconfig
> index f86dd4ce7d0d..2c9d5a644ae9 100644
> --- a/arch/arm/configs/aspeed_g4_defconfig
> +++ b/arch/arm/configs/aspeed_g4_defconfig
> @@ -249,7 +249,7 @@ CONFIG_DEBUG_INFO_REDUCED=y
> CONFIG_GDB_SCRIPTS=y
> CONFIG_STRIP_ASM_SYMS=y
> CONFIG_DEBUG_FS=y
> -CONFIG_ARM_DEBUG_WX=y
> +CONFIG_ARM_CHECK_WX=y
> CONFIG_SCHED_STACK_END_CHECK=y
> CONFIG_PANIC_ON_OOPS=y
> CONFIG_PANIC_TIMEOUT=-1
> diff --git a/arch/arm/configs/aspeed_g5_defconfig b/arch/arm/configs/aspeed_g5_defconfig
> index 45b937419dbd..1327a09e163a 100644
> --- a/arch/arm/configs/aspeed_g5_defconfig
> +++ b/arch/arm/configs/aspeed_g5_defconfig
> @@ -300,7 +300,7 @@ CONFIG_DEBUG_INFO_REDUCED=y
> CONFIG_GDB_SCRIPTS=y
> CONFIG_STRIP_ASM_SYMS=y
> CONFIG_DEBUG_FS=y
> -CONFIG_ARM_DEBUG_WX=y
> +CONFIG_ARM_CHECK_WX=y
> CONFIG_SCHED_STACK_END_CHECK=y
> CONFIG_PANIC_ON_OOPS=y
> CONFIG_PANIC_TIMEOUT=-1
> diff --git a/arch/arm/configs/shmobile_defconfig b/arch/arm/configs/shmobile_defconfig
> index 6f9696e9fe17..cc22e22b989e 100644
> --- a/arch/arm/configs/shmobile_defconfig
> +++ b/arch/arm/configs/shmobile_defconfig
> @@ -225,4 +225,4 @@ CONFIG_CMA_SIZE_MBYTES=64
> CONFIG_PRINTK_TIME=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_DEBUG_FS=y
> -CONFIG_ARM_DEBUG_WX=y
> +CONFIG_ARM_CHECK_WX=y
> diff --git a/arch/arm/include/asm/ptdump.h b/arch/arm/include/asm/ptdump.h
> index 46a4575146ee..3c5245220ecf 100644
> --- a/arch/arm/include/asm/ptdump.h
> +++ b/arch/arm/include/asm/ptdump.h
> @@ -32,10 +32,10 @@ void ptdump_check_wx(void);
>
> #endif /* CONFIG_ARM_PTDUMP_CORE */
>
> -#ifdef CONFIG_ARM_DEBUG_WX
> -#define arm_debug_checkwx() ptdump_check_wx()
> +#ifdef CONFIG_ARM_CHECK_WX
> +#define arm_pgtable_checkwx() ptdump_check_wx()
> #else
> -#define arm_debug_checkwx() do { } while (0)
> +#define arm_pgtable_checkwx() do { } while (0)
> #endif
>
> #endif /* __ASM_PTDUMP_H */
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 0cc1bf04686d..c515faf22eeb 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -403,7 +403,7 @@ static int __mark_rodata_ro(void *unused)
> void mark_rodata_ro(void)
> {
> stop_machine(__mark_rodata_ro, NULL, NULL);
> - arm_debug_checkwx();
> + arm_pgtable_checkwx();
> }
>
> #else
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b5a51b0ef944..7e120fb21c58 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -11,7 +11,7 @@ config ARM64
> select ACPI_MCFG if (ACPI && PCI)
> select ACPI_SPCR_TABLE if ACPI
> select ACPI_PPTT if ACPI
> - select ARCH_HAS_DEBUG_WX
> + select ARCH_HAS_CHECK_WX
> select ARCH_BINFMT_ELF_EXTRA_PHDRS
> select ARCH_BINFMT_ELF_STATE
> select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 2580e27e4328..7c1fe5b4cd41 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -130,7 +130,7 @@ config PPC
> select ARCH_HAS_CURRENT_STACK_POINTER
> select ARCH_HAS_DEBUG_VIRTUAL
> select ARCH_HAS_DEBUG_VM_PGTABLE
> - select ARCH_HAS_DEBUG_WX if STRICT_KERNEL_RWX
> + select ARCH_HAS_CHECK_WX if STRICT_KERNEL_RWX
> select ARCH_HAS_DEVMEM_IS_ALLOWED
> select ARCH_HAS_DMA_MAP_DIRECT if PPC_PSERIES
> select ARCH_HAS_DMA_OPS if PPC64
> diff --git a/arch/powerpc/configs/ppc64_defconfig b/arch/powerpc/configs/ppc64_defconfig
> index 1eb8e3457e8b..5c33f0bba0e3 100644
> --- a/arch/powerpc/configs/ppc64_defconfig
> +++ b/arch/powerpc/configs/ppc64_defconfig
> @@ -393,7 +393,7 @@ CONFIG_MAGIC_SYSRQ=y
> CONFIG_PAGE_OWNER=y
> CONFIG_PAGE_POISONING=y
> CONFIG_DEBUG_RODATA_TEST=y
> -CONFIG_DEBUG_WX=y
> +CONFIG_CHECK_WX=y
> CONFIG_DEBUG_STACK_USAGE=y
> CONFIG_DEBUG_VM=y
> # CONFIG_DEBUG_VM_PGTABLE is not set
> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
> index 0d499aebee72..3451351b756b 100644
> --- a/arch/powerpc/mm/ptdump/ptdump.c
> +++ b/arch/powerpc/mm/ptdump/ptdump.c
> @@ -191,7 +191,7 @@ static void note_prot_wx(struct pg_state *st, unsigned long addr)
> if (!pte_write(pte) || !pte_exec(pte))
> return;
>
> - WARN_ONCE(IS_ENABLED(CONFIG_DEBUG_WX),
> + WARN_ONCE(IS_ENABLED(CONFIG_CHECK_WX),
> "powerpc/mm: Found insecure W+X mapping at address %p/%pS\n",
> (void *)st->start_address, (void *)st->start_address);
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index d6c2dbf8455c..05e33d4d5efa 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -29,7 +29,7 @@ config RISCV
> select ARCH_HAS_CURRENT_STACK_POINTER
> select ARCH_HAS_DEBUG_VIRTUAL if MMU
> select ARCH_HAS_DEBUG_VM_PGTABLE
> - select ARCH_HAS_DEBUG_WX
> + select ARCH_HAS_CHECK_WX
> select ARCH_HAS_DELAY_TIMER
> select ARCH_HAS_ELF_CORE_EFLAGS if BINFMT_ELF && ELF_CORE
> select ARCH_HAS_FAST_MULTIPLIER
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 4b51bc6e8948..11b76f2b0f80 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -92,7 +92,7 @@ config S390
> select ARCH_HAS_CURRENT_STACK_POINTER
> select ARCH_HAS_DEBUG_VIRTUAL
> select ARCH_HAS_DEBUG_VM_PGTABLE
> - select ARCH_HAS_DEBUG_WX
> + select ARCH_HAS_CHECK_WX
> select ARCH_HAS_DEVMEM_IS_ALLOWED
> select ARCH_HAS_DMA_OPS if PCI
> select ARCH_HAS_ELF_RANDOMIZE
> diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig
> index 3dae71474333..68d53c0bc8db 100644
> --- a/arch/s390/configs/debug_defconfig
> +++ b/arch/s390/configs/debug_defconfig
> @@ -841,7 +841,7 @@ CONFIG_DEBUG_PAGEALLOC=y
> CONFIG_SLUB_DEBUG_ON=y
> CONFIG_PAGE_OWNER=y
> CONFIG_DEBUG_RODATA_TEST=y
> -CONFIG_DEBUG_WX=y
> +CONFIG_CHECK_WX=y
> CONFIG_PTDUMP_DEBUGFS=y
> CONFIG_DEBUG_OBJECTS=y
> CONFIG_DEBUG_OBJECTS_SELFTEST=y
> diff --git a/arch/s390/configs/defconfig b/arch/s390/configs/defconfig
> index 6f5722634b4d..8e5cfc695121 100644
> --- a/arch/s390/configs/defconfig
> +++ b/arch/s390/configs/defconfig
> @@ -820,7 +820,7 @@ CONFIG_DEBUG_INFO_DWARF4=y
> CONFIG_GDB_SCRIPTS=y
> CONFIG_DEBUG_SECTION_MISMATCH=y
> CONFIG_MAGIC_SYSRQ=y
> -CONFIG_DEBUG_WX=y
> +CONFIG_CHECK_WX=y
> CONFIG_PTDUMP_DEBUGFS=y
> CONFIG_DEBUG_MEMORY_INIT=y
> CONFIG_PANIC_ON_OOPS=y
> diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
> index 89badbe72ae7..a23a0bd4d8a8 100644
> --- a/arch/s390/mm/dump_pagetables.c
> +++ b/arch/s390/mm/dump_pagetables.c
> @@ -86,7 +86,7 @@ static void note_prot_wx(struct pg_state *st, unsigned long addr)
> */
> if (addr == PAGE_SIZE && (nospec_uses_trampoline() || !cpu_has_bear()))
> return;
> - WARN_ONCE(IS_ENABLED(CONFIG_DEBUG_WX),
> + WARN_ONCE(IS_ENABLED(CONFIG_CHECK_WX),
> "s390/mm: Found insecure W+X mapping at address %pS\n",
> (void *)st->start_address);
> st->wx_pages += (addr - st->start_address) / PAGE_SIZE;
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 15fd9ec5ecac..170cfcb06174 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -110,7 +110,7 @@ config X86
> select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
> select ARCH_HAS_SYSCALL_WRAPPER
> select ARCH_HAS_UBSAN
> - select ARCH_HAS_DEBUG_WX
> + select ARCH_HAS_CHECK_WX
> select ARCH_HAS_ZONE_DMA_SET if EXPERT
> select ARCH_HAVE_NMI_SAFE_CMPXCHG
> select ARCH_HAVE_EXTRA_ELF_NOTES
> diff --git a/arch/x86/configs/x86_64_defconfig b/arch/x86/configs/x86_64_defconfig
> index 269f7d808be4..e6896aeb77d8 100644
> --- a/arch/x86/configs/x86_64_defconfig
> +++ b/arch/x86/configs/x86_64_defconfig
> @@ -263,7 +263,7 @@ CONFIG_SECURITY_SELINUX_BOOTPARAM=y
> CONFIG_PRINTK_TIME=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_MAGIC_SYSRQ=y
> -CONFIG_DEBUG_WX=y
> +CONFIG_CHECK_WX=y
> CONFIG_DEBUG_STACK_USAGE=y
> CONFIG_SCHEDSTATS=y
> CONFIG_BLK_DEV_IO_TRACE=y
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index d551120a7c88..ef0252a09c28 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -41,10 +41,10 @@ void ptdump_walk_user_pgd_level_checkwx(void);
> #define pgprot_encrypted(prot) __pgprot(cc_mkenc(pgprot_val(prot)))
> #define pgprot_decrypted(prot) __pgprot(cc_mkdec(pgprot_val(prot)))
>
> -#ifdef CONFIG_DEBUG_WX
> -#define debug_checkwx_user() ptdump_walk_user_pgd_level_checkwx()
> +#ifdef CONFIG_CHECK_WX
> +#define pgtable_checkwx_user() ptdump_walk_user_pgd_level_checkwx()
> #else
> -#define debug_checkwx_user() do { } while (0)
> +#define pgtable_checkwx_user() do { } while (0)
> #endif
>
> extern spinlock_t pgd_lock;
> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> index 598f553cc871..31055ee6f1de 100644
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -688,5 +688,5 @@ void pti_finalize(void)
> pti_clone_entry_text(true);
> pti_clone_kernel_text();
>
> - debug_checkwx_user();
> + pgtable_checkwx_user();
> }
> diff --git a/include/linux/ptdump.h b/include/linux/ptdump.h
> index 240bd3bff18d..af18d1459b2f 100644
> --- a/include/linux/ptdump.h
> +++ b/include/linux/ptdump.h
> @@ -31,9 +31,9 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
> void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd);
> bool ptdump_check_wx(void);
>
> -static inline void debug_checkwx(void)
> +static inline void pgtable_checkwx(void)
> {
> - if (IS_ENABLED(CONFIG_DEBUG_WX))
> + if (IS_ENABLED(CONFIG_CHECK_WX))
> ptdump_check_wx();
> }
>
> diff --git a/init/main.c b/init/main.c
> index 31f2bf54976a..a87a3d52f3e2 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1535,7 +1535,7 @@ static void mark_readonly(void)
> flush_module_init_free_work();
> jump_label_init_ro();
> mark_rodata_ro();
> - debug_checkwx();
> + pgtable_checkwx();
> rodata_test();
> } else if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
> pr_info("Kernel memory protection disabled.\n");
> diff --git a/kernel/configs/debug.config b/kernel/configs/debug.config
> index 307c97ac5fa9..ac878669c193 100644
> --- a/kernel/configs/debug.config
> +++ b/kernel/configs/debug.config
> @@ -50,7 +50,7 @@ CONFIG_DEBUG_NET=y
> # CONFIG_DEBUG_PAGEALLOC is not set
> # CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF is not set
> # CONFIG_DEBUG_RODATA_TEST is not set
> -# CONFIG_DEBUG_WX is not set
> +# CONFIG_CHECK_WX is not set
> # CONFIG_KFENCE is not set
> # CONFIG_PAGE_POISONING is not set
> # CONFIG_SLUB_STATS is not set
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 604c58199acb..ffbc641cc31f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1511,6 +1511,47 @@ config LAZY_MMU_MODE_KUNIT_TEST
>
> If unsure, say N.
>
> +config ARCH_HAS_CHECK_WX
> + bool
> +
> +config CHECK_WX
> + bool "Warn on W+X mappings at boot"
> + default STRICT_KERNEL_RWX
> + depends on ARCH_HAS_CHECK_WX
> + depends on ARCH_HAS_PTDUMP
> + depends on MMU
> + select PTDUMP
> + 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 ARCH_HAS_PTDUMP
> + bool
> +
> +config PTDUMP
> + bool
> +
> +
> source "mm/damon/Kconfig"
>
> endmenu
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 15dca19dd07d..75b44e4a6e36 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -180,45 +180,6 @@ config DEBUG_RODATA_TEST
> 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 ARCH_HAS_PTDUMP
> - depends on MMU
> - select PTDUMP
> - 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 ARCH_HAS_PTDUMP
> - bool
> -
> -config PTDUMP
> - bool
> -
> config PTDUMP_DEBUGFS
> bool "Export kernel pagetable layout to userspace via debugfs"
> depends on DEBUG_KERNEL
>
> ---
> base-commit: 93f51579e7df248780214094418f205253383cc5
> change-id: 20260925-direct-map-verify-wx-b81bda879781
>
> --
> Sincerely yours,
> Mike.
>
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