@@ -1537,6 +1537,10 @@ config ARM64_PTR_AUTH
This feature works with FUNCTION_GRAPH_TRACER option only if
DYNAMIC_FTRACE_WITH_REGS is enabled.
+config CC_HAS_BRANCH_PROT_NONE
+ # GCC 9 or later, clang 8 or later
+ def_bool $(cc-option,-mbranch-protection=none)
+
config CC_HAS_BRANCH_PROT_PAC_RET
# GCC 9 or later, clang 8 or later
def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
@@ -65,6 +65,10 @@ stack_protector_prepare: prepare0
include/generated/asm-offsets.h))
endif
+# Ensure that if the compiler supports branch protection we default it
+# off, this will be overridden if we are using branch protection.
+branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_NONE) := -mbranch-protection=none
+
ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
@@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa
# we pass it only to the assembler. This option is utilized only in case of non
# integrated assemblers.
branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a
-KBUILD_CFLAGS += $(branch-prot-flags-y)
endif
+KBUILD_CFLAGS += $(branch-prot-flags-y)
+
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
CHECKFLAGS += -D__AARCH64EB__
Compilers with branch protection support can be configured to enable it by default, it is likely that distributions will do this as part of deploying branch protection system wide. As well as the slight overhead from having some extra NOPs for unused branch protection features this can cause more serious problems when the kernel is providing pointer authentication to userspace but not built for pointer authentication itself. In that case our switching of keys for userspace can affect the kernel unexpectedly, causing pointer authentication instructions in the kernel to corrupt addresses. To ensure that we get consistent and reliable behaviour always explicitly initialise the branch protection mode, ensuring that the kernel is built the same way regardless of the compiler defaults. Fixes: 7503197562567 (arm64: add basic pointer authentication support) Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com> Signed-off-by: Mark Brown <broonie@kernel.org> Cc: stable@vger.kernel.org --- arch/arm64/Kconfig | 4 ++++ arch/arm64/Makefile | 7 ++++++- 2 files changed, 10 insertions(+), 1 deletion(-)