[PATCH v3 1/2] arm64: Add ARM64_PTR_AUTH_KERNEL config option

[Daniel Kiss]

This patch add the ARM64_PTR_AUTH_KERNEL config and deals with the
build aspect of it.

Userspace support has no dependency on the toolchain therefore all
toolchain checks and build flags are controlled the new config
option.
The default config behavior will not be changed.

Signed-off-by: Daniel Kiss <daniel.kiss at arm.com>
---
 arch/arm64/Kconfig              | 33 +++++++++++++++++++--------------
 arch/arm64/Makefile             |  2 +-
 arch/arm64/kernel/asm-offsets.c |  2 ++
 drivers/misc/lkdtm/bugs.c       |  6 +++---
 4 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f39568b28ec1..c1268cdd6964 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1474,12 +1474,6 @@ menu "ARMv8.3 architectural features"
 config ARM64_PTR_AUTH
 	bool "Enable support for pointer authentication"
 	default y
-	depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC
-	# Modern compilers insert a .note.gnu.property section note for PAC
-	# which is only understood by binutils starting with version 2.33.1.
-	depends on LD_IS_LLD || LD_VERSION >= 233010000 || (CC_IS_GCC && GCC_VERSION < 90100)
-	depends on !CC_IS_CLANG || AS_HAS_CFI_NEGATE_RA_STATE
-	depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
 	help
 	  Pointer authentication (part of the ARMv8.3 Extensions) provides
 	  instructions for signing and authenticating pointers against secret
@@ -1491,13 +1485,6 @@ config ARM64_PTR_AUTH
 	  for each process at exec() time, with these keys being
 	  context-switched along with the process.
 
-	  If the compiler supports the -mbranch-protection or
-	  -msign-return-address flag (e.g. GCC 7 or later), then this option
-	  will also cause the kernel itself to be compiled with return address
-	  protection. In this case, and if the target hardware is known to
-	  support pointer authentication, then CONFIG_STACKPROTECTOR can be
-	  disabled with minimal loss of protection.
-
 	  The feature is detected at runtime. If the feature is not present in
 	  hardware it will not be advertised to userspace/KVM guest nor will it
 	  be enabled.
@@ -1508,6 +1495,24 @@ config ARM64_PTR_AUTH
 	  but with the feature disabled. On such a system, this option should
 	  not be selected.
 
+config ARM64_PTR_AUTH_KERNEL
+	bool "Use pointer authentication for kernel"
+	default y
+	depends on ARM64_PTR_AUTH
+	depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC
+	# Modern compilers insert a .note.gnu.property section note for PAC
+	# which is only understood by binutils starting with version 2.33.1.
+	depends on LD_IS_LLD || LD_VERSION >= 233010000 || (CC_IS_GCC && GCC_VERSION < 90100)
+	depends on !CC_IS_CLANG || AS_HAS_CFI_NEGATE_RA_STATE
+	depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
+	help
+	  If the compiler supports the -mbranch-protection or
+	  -msign-return-address flag (e.g. GCC 7 or later), then this option
+	  will cause the kernel itself to be compiled with return address
+	  protection. In this case, and if the target hardware is known to
+	  support pointer authentication, then CONFIG_STACKPROTECTOR can be
+	  disabled with minimal loss of protection.
+
 	  This feature works with FUNCTION_GRAPH_TRACER option only if
 	  DYNAMIC_FTRACE_WITH_REGS is enabled.
 
@@ -1599,7 +1604,7 @@ config ARM64_BTI_KERNEL
 	bool "Use Branch Target Identification for kernel"
 	default y
 	depends on ARM64_BTI
-	depends on ARM64_PTR_AUTH
+	depends on ARM64_PTR_AUTH_KERNEL
 	depends on CC_HAS_BRANCH_PROT_PAC_RET_BTI
 	# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94697
 	depends on !CC_IS_GCC || GCC_VERSION >= 100100
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 90309208bb28..a50b5e8231a7 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -70,7 +70,7 @@ endif
 # off, this will be overridden if we are using branch protection.
 branch-prot-flags-y += $(call cc-option,-mbranch-protection=none)
 
-ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
+ifeq ($(CONFIG_ARM64_PTR_AUTH_KERNEL),y)
 branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
 # We enable additional protection for leaf functions as there is some
 # narrow potential for ROP protection benefits and no substantial
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 301784463587..21c9f98f868d 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -45,6 +45,8 @@ int main(void)
   DEFINE(THREAD_CPU_CONTEXT,	offsetof(struct task_struct, thread.cpu_context));
 #ifdef CONFIG_ARM64_PTR_AUTH
   DEFINE(THREAD_KEYS_USER,	offsetof(struct task_struct, thread.keys_user));
+#endif
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
   DEFINE(THREAD_KEYS_KERNEL,	offsetof(struct task_struct, thread.keys_kernel));
 #endif
 #ifdef CONFIG_ARM64_MTE
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 110f5a8538e9..b5b809b3e1ef 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -446,7 +446,7 @@ void lkdtm_DOUBLE_FAULT(void)
 #ifdef CONFIG_ARM64
 static noinline void change_pac_parameters(void)
 {
-	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) {
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
 		/* Reset the keys of current task */
 		ptrauth_thread_init_kernel(current);
 		ptrauth_thread_switch_kernel(current);
@@ -460,8 +460,8 @@ noinline void lkdtm_CORRUPT_PAC(void)
 #define CORRUPT_PAC_ITERATE	10
 	int i;
 
-	if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH))
-		pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH\n");
+	if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL))
+		pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n");
 
 	if (!system_supports_address_auth()) {
 		pr_err("FAIL: CPU lacks pointer authentication feature\n");
-- 
2.25.1