arm64: Add ARM64_PTR_AUTH_KERNEL config option

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@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210613092632.93591-2-daniel.kiss@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9f1d8566bbf95c9e56c2f284482edab5d9d92cb7..489e3e42320f1c0f65e51b669089fd0346b249ea 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1481,12 +1481,6 @@ 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 >= 23301 || (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
@@ -1498,13 +1492,6 @@ 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.
@@ -1515,6 +1502,24 @@ 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
+       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 >= 23301 || (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.
 
@@ -1606,7 +1611,7 @@ 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 b52481f0605d8e43010d41de5810b53101c47a0b..3b5b1c480449cb83bad48ff46ba5ac630a64751b 100644 (file)
--- 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 0cb34ccb6e7330757118d727a230d934ce050d36..03420b89c60296c691133075aa8d4112f4d60e19 100644 (file)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -46,6 +46,8 @@ int main(void)
   DEFINE(THREAD_SCTLR_USER,    offsetof(struct task_struct, thread.sctlr_user));
 #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 0e8254d0cf0ba83b6e0a40d515e972aed30498d9..a164896dc6d4c3c376efa2742ea98c33880fc935 100644 (file)
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -463,7 +463,7 @@ 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);
@@ -477,8 +477,8 @@ 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");