[PATCH] arm64: always enable DEBUG_RODATA and remove the Kconfig option

Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
make these protections a fundamental security feature rather than an
opt-in. This also results in a minor code simplification.

For those rare cases when users wish to disable this protection (e.g.
for debugging), this can be done by passing 'rodata=off' on the command
line.

As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
tradeoff, and does not affect correctness, this is left user-selectable.
DEBUG_MODULE_RONX is also left user-selectable until the core code
provides a boot-time option to disable the protection for debugging
use-cases.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kees Cook <redacted>
Cc: Laura Abbott <redacted>
Cc: Will Deacon <redacted>
---
 arch/arm64/Kconfig       |  3 +++
 arch/arm64/Kconfig.debug | 10 ----------
 arch/arm64/kernel/insn.c |  2 +-
 3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index bc3f00f..43d6134 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -122,6 +122,9 @@ 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

diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 0cc758c..b661fe7 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug

@@ -49,16 +49,6 @@ config DEBUG_SET_MODULE_RONX
 
 	  If in doubt, say Y.
 
-config DEBUG_RODATA
-	bool "Make kernel text and rodata read-only"
-	default y
-	help
-	  If this is set, kernel 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"

diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index 63f9432..178488f 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c

@@ -96,7 +96,7 @@ static void __kprobes *patch_map(void *addr, int fixmap)
 
 	if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
 		page = vmalloc_to_page(addr);
-	else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
+	else if (!module)
 		page = pfn_to_page(PHYS_PFN(__pa(addr)));
 	else
 		return addr;

-- 
2.7.4

On 25 August 2016 at 18:23, Mark Rutland [off-list ref] wrote:

Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
make these protections a fundamental security feature rather than an
opt-in. This also results in a minor code simplification.

For those rare cases when users wish to disable this protection (e.g.
for debugging), this can be done by passing 'rodata=off' on the command
line.

As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
tradeoff, and does not affect correctness, this is left user-selectable.
DEBUG_MODULE_RONX is also left user-selectable until the core code
provides a boot-time option to disable the protection for debugging
use-cases.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

Acked-by: Ard Biesheuvel <redacted>

About time!

On Thu, Aug 25, 2016 at 12:23 PM, Mark Rutland [off-list ref] wrote:

Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
make these protections a fundamental security feature rather than an
opt-in. This also results in a minor code simplification.

For those rare cases when users wish to disable this protection (e.g.
for debugging), this can be done by passing 'rodata=off' on the command
line.

As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
tradeoff, and does not affect correctness, this is left user-selectable.
DEBUG_MODULE_RONX is also left user-selectable until the core code
provides a boot-time option to disable the protection for debugging
use-cases.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kees Cook <redacted>
Cc: Laura Abbott <redacted>
Cc: Will Deacon <redacted>

Awesome!

Acked-by: Kees Cook <redacted>

-Kees

-- 
Kees Cook
Nexus Security

On 08/25/2016 09:23 AM, Mark Rutland wrote:

Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
make these protections a fundamental security feature rather than an
opt-in. This also results in a minor code simplification.

For those rare cases when users wish to disable this protection (e.g.
for debugging), this can be done by passing 'rodata=off' on the command
line.

As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
tradeoff, and does not affect correctness, this is left user-selectable.
DEBUG_MODULE_RONX is also left user-selectable until the core code
provides a boot-time option to disable the protection for debugging
use-cases.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kees Cook <redacted>
Cc: Laura Abbott <redacted>
Cc: Will Deacon <redacted>

Excellent!

Acked-by: Laura Abbott <redacted>

On Thu, Aug 25, 2016 at 05:23:23PM +0100, Mark Rutland wrote:

Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
make these protections a fundamental security feature rather than an
opt-in. This also results in a minor code simplification.

For those rare cases when users wish to disable this protection (e.g.
for debugging), this can be done by passing 'rodata=off' on the command
line.

As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
tradeoff, and does not affect correctness, this is left user-selectable.
DEBUG_MODULE_RONX is also left user-selectable until the core code
provides a boot-time option to disable the protection for debugging
use-cases.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kees Cook <redacted>
Cc: Laura Abbott <redacted>
Cc: Will Deacon <redacted>
---
 arch/arm64/Kconfig       |  3 +++
 arch/arm64/Kconfig.debug | 10 ----------
 arch/arm64/kernel/insn.c |  2 +-
 3 files changed, 4 insertions(+), 11 deletions(-)

This is a very popular patch.

Applied for 4.9. Perhaps it makes up for all the unpopular patches I've
applied in the past.

Will