arch: Move CONFIG_DEBUG_RODATA and CONFIG_SET_MODULE_RONX to be common

There are multiple architectures that support CONFIG_DEBUG_RODATA and
CONFIG_SET_MODULE_RONX. These options also now have the ability to be
turned off at runtime. Move these to an architecture independent
location and make these options def_bool y for almost all of those
arches.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

Documentation/security/self-protection.txt

@@ -56,6 +56,12 @@ CONFIG_DEBUG_SET_MODULE_RONX, which seek to make sure that code is not
 writable, data is not executable, and read-only data is neither writable
 nor executable.
 
+Most architectures have these options on by default and not user selectable.
+For some architectures like arm that wish to have these be selectable,
+the architecture Kconfig can select ARCH_OPTIONAL_KERNEL_RWX to enable
+a Kconfig prompt. CONFIG_ARCH_OPTIONAL_KERNEL_RWX_DEFAULT determines
+the default setting when ARCH_OPTIONAL_KERNEL_RWX is enabled.
+
 #### Function pointers and sensitive variables must not be writable
 
 Vast areas of kernel memory contain function pointers that are looked

arch/Kconfig

@@ -781,4 +781,38 @@ config VMAP_STACK
 	  the stack to map directly to the KASAN shadow map using a formula
 	  that is incorrect if the stack is in vmalloc space.
 
+config ARCH_OPTIONAL_KERNEL_RWX
+	def_bool n
+
+config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
+	def_bool n
+
+config ARCH_HAS_STRICT_KERNEL_RWX
+	def_bool n
+
+config DEBUG_RODATA
+	bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
+	depends on ARCH_HAS_STRICT_KERNEL_RWX
+	default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
+	help
+	  If this is set, kernel text and rodata memory will be made read-only,
+	  and non-text memory will be made non-executable. This provides
+	  protection against certain security exploits (e.g. executing the heap
+	  or modifying text)
+
+	  These features are considered standard security practice these days.
+	  You should say Y here in almost all cases.
+
+config ARCH_HAS_STRICT_MODULE_RWX
+	def_bool n
+
+config DEBUG_SET_MODULE_RONX
+	bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
+	depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
+	default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
+	help
+	  If this is set, module text and rodata memory will be made read-only,
+	  and non-text memory will be made non-executable. This provides
+	  protection against certain security exploits (e.g. writing to text)
+
 source "kernel/gcov/Kconfig"

arch/arm/Kconfig

@@ -4,10 +4,14 @@ config ARM
 	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
+	select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL
+	select ARCH_HAS_STRICT_MODULE_RWX if MMU
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAVE_CUSTOM_GPIO_H
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_MIGHT_HAVE_PC_PARPORT
+	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF

arch/arm/Kconfig.debug

@@ -1738,17 +1738,6 @@ config PID_IN_CONTEXTIDR
 	  additional instructions during context switch. Say Y here only if you
 	  are planning to use hardware trace tools with this kernel.
 
-config DEBUG_SET_MODULE_RONX
-	bool "Set loadable kernel module data as NX and text as RO"
-	depends on MODULES && MMU
-	---help---
-	  This option helps catch unintended modifications to loadable
-	  kernel module's text and read-only data. It also prevents execution
-	  of module data. Such protection may interfere with run-time code
-	  patching and dynamic kernel tracing - and they might also protect
-	  against certain classes of kernel exploits.
-	  If in doubt, say "N".
-
 source "drivers/hwtracing/coresight/Kconfig"
 
 endmenu

arch/arm/mm/Kconfig

@@ -1051,18 +1051,6 @@ config ARCH_SUPPORTS_BIG_ENDIAN
 	  This option specifies the architecture can support big endian
 	  operation.
 
-config DEBUG_RODATA
-	bool "Make kernel text and rodata read-only"
-	depends on MMU && !XIP_KERNEL
-	default y if CPU_V7
-	help
-	  If this is set, kernel text and rodata memory will be made
-	  read-only, and non-text kernel memory will be made non-executable.
-	  The tradeoff is that each region is padded to section-size (1MiB)
-	  boundaries (because their permissions are different and splitting
-	  the 1M pages into 4K ones causes TLB performance problems), which
-	  can waste memory.
-
 config DEBUG_ALIGN_RODATA
 	bool "Make rodata strictly non-executable"
 	depends on DEBUG_RODATA

arch/arm64/Kconfig

@@ -13,6 +13,8 @@ config ARM64
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_SG_CHAIN
+	select ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_HAS_STRICT_MODULE_RWX
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_SUPPORTS_ATOMIC_RMW
@@ -123,9 +125,6 @@ config ARCH_PHYS_ADDR_T_64BIT
 config MMU
 	def_bool y
 
-config DEBUG_RODATA
-	def_bool y
-
 config ARM64_PAGE_SHIFT
 	int
 	default 16 if ARM64_64K_PAGES

arch/arm64/Kconfig.debug

@@ -71,17 +71,6 @@ config DEBUG_WX
 
 	  If in doubt, say "Y".
 
-config DEBUG_SET_MODULE_RONX
-	bool "Set loadable kernel module data as NX and text as RO"
-	depends on MODULES
-	default y
-	help
-	  Is this is set, kernel module text and rodata will be made read-only.
-	  This is to help catch accidental or malicious attempts to change the
-	  kernel's executable code.
-
-	  If in doubt, say Y.
-
 config DEBUG_ALIGN_RODATA
 	depends on DEBUG_RODATA
 	bool "Align linker sections up to SECTION_SIZE"

arch/parisc/Kconfig

@@ -8,6 +8,7 @@ config PARISC
 	select HAVE_SYSCALL_TRACEPOINTS
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_HAS_ELF_RANDOMIZE
+	select ARCH_HAS_STRICT_KERNEL_RWX
 	select RTC_CLASS
 	select RTC_DRV_GENERIC
 	select INIT_ALL_POSSIBLE

arch/parisc/Kconfig.debug

@@ -5,15 +5,4 @@ source "lib/Kconfig.debug"
 config TRACE_IRQFLAGS_SUPPORT
 	def_bool y
 
-config DEBUG_RODATA
-       bool "Write protect kernel read-only data structures"
-       depends on DEBUG_KERNEL
-       default y
-       help
-         Mark the kernel read-only data as write-protected in the pagetables,
-         in order to catch accidental (and incorrect) writes to such const
-         data. This option may have a slight performance impact because a
-         portion of the kernel code won't be covered by a TLB anymore.
-         If in doubt, say "N".
-
 endmenu

arch/s390/Kconfig

@@ -62,9 +62,6 @@ config PCI_QUIRKS
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
 
-config DEBUG_RODATA
-	def_bool y
-
 config S390
 	def_bool y
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
@@ -73,6 +70,8 @@ config S390
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_SG_CHAIN
+	select ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_HAS_STRICT_MODULE_RWX
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select ARCH_INLINE_READ_LOCK

arch/s390/Kconfig.debug

@@ -17,7 +17,4 @@ config S390_PTDUMP
 	  kernel.
 	  If in doubt, say "N"
 
-config DEBUG_SET_MODULE_RONX
-	def_bool y
-	depends on MODULES
 endmenu

arch/x86/Kconfig

@@ -54,6 +54,8 @@ config X86
 	select ARCH_HAS_MMIO_FLUSH
 	select ARCH_HAS_PMEM_API		if X86_64
 	select ARCH_HAS_SG_CHAIN
+	select ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_HAS_STRICT_MODULE_RWX
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select ARCH_MIGHT_HAVE_ACPI_PDC		if ACPI
@@ -309,9 +311,6 @@ config ARCH_SUPPORTS_UPROBES
 config FIX_EARLYCON_MEM
 	def_bool y
 
-config DEBUG_RODATA
-	def_bool y
-
 config PGTABLE_LEVELS
 	int
 	default 4 if X86_64

arch/x86/Kconfig.debug

@@ -109,17 +109,6 @@ config DEBUG_WX
 
 	  If in doubt, say "Y".
 
-config DEBUG_SET_MODULE_RONX
-	bool "Set loadable kernel module data as NX and text as RO"
-	depends on MODULES
-	---help---
-	  This option helps catch unintended modifications to loadable
-	  kernel module's text and read-only data. It also prevents execution
-	  of module data. Such protection may interfere with run-time code
-	  patching and dynamic kernel tracing - and they might also protect
-	  against certain classes of kernel exploits.
-	  If in doubt, say "N".
-
 config DEBUG_NX_TEST
 	tristate "Testcase for the NX non-executable stack feature"
 	depends on DEBUG_KERNEL && m