From 74afda4016a7437e6e425c3370e4b93b47be8ddf Mon Sep 17 00:00:00 2001 From: Kristina Martsenko Date: Fri, 13 Mar 2020 14:35:03 +0530 Subject: [PATCH] arm64: compile the kernel with ptrauth return address signing Compile all functions with two ptrauth instructions: PACIASP in the prologue to sign the return address, and AUTIASP in the epilogue to authenticate the return address (from the stack). If authentication fails, the return will cause an instruction abort to be taken, followed by an oops and killing the task. This should help protect the kernel against attacks using return-oriented programming. As ptrauth protects the return address, it can also serve as a replacement for CONFIG_STACKPROTECTOR, although note that it does not protect other parts of the stack. The new instructions are in the HINT encoding space, so on a system without ptrauth they execute as NOPs. CONFIG_ARM64_PTR_AUTH now not only enables ptrauth for userspace and KVM guests, but also automatically builds the kernel with ptrauth instructions if the compiler supports it. If there is no compiler support, we do not warn that the kernel was built without ptrauth instructions. GCC 7 and 8 support the -msign-return-address option, while GCC 9 deprecates that option and replaces it with -mbranch-protection. Support both options. Clang uses an external assembler hence this patch makes sure that the correct parameters (-march=armv8.3-a) are passed down to help it recognize the ptrauth instructions. Ftrace function tracer works properly with Ptrauth only when patchable-function-entry feature is present and is ensured by the Kconfig dependency. Cc: Catalin Marinas Cc: Will Deacon Cc: Masahiro Yamada Reviewed-by: Kees Cook Reviewed-by: Vincenzo Frascino # not co-dev parts Co-developed-by: Vincenzo Frascino Signed-off-by: Vincenzo Frascino Signed-off-by: Kristina Martsenko [Amit: Cover leaf function, comments, Ftrace Kconfig] Signed-off-by: Amit Daniel Kachhap Signed-off-by: Catalin Marinas --- arch/arm64/Kconfig | 24 +++++++++++++++++++++++- arch/arm64/Makefile | 11 +++++++++++ 2 files changed, 34 insertions(+), 1 deletion(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 115ceea..155041a 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1499,6 +1499,8 @@ config ARM64_PTR_AUTH bool "Enable support for pointer authentication" default y depends on !KVM || ARM64_VHE + depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC + 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 @@ -1506,11 +1508,17 @@ config ARM64_PTR_AUTH and other attacks. This option enables these instructions at EL0 (i.e. for userspace). - Choosing this option will cause the kernel to initialise secret keys 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. However, KVM guest also require VHE mode and hence @@ -1522,6 +1530,20 @@ config ARM64_PTR_AUTH but with the feature disabled. On such a system, this option should not be selected. + This feature works with FUNCTION_GRAPH_TRACER option only if + DYNAMIC_FTRACE_WITH_REGS is enabled. + +config CC_HAS_BRANCH_PROT_PAC_RET + # GCC 9 or later, clang 8 or later + def_bool $(cc-option,-mbranch-protection=pac-ret+leaf) + +config CC_HAS_SIGN_RETURN_ADDRESS + # GCC 7, 8 + def_bool $(cc-option,-msign-return-address=all) + +config AS_HAS_PAC + def_bool $(as-option,-Wa$(comma)-march=armv8.3-a) + endmenu menu "ARMv8.5 architectural features" diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index dca1a97..f15f92b 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -65,6 +65,17 @@ stack_protector_prepare: prepare0 include/generated/asm-offsets.h)) endif +ifeq ($(CONFIG_ARM64_PTR_AUTH),y) +branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf +# -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the +# compiler to generate them and consequently to break the single image contract +# we pass it only to the assembler. This option is utilized only in case of non +# integrated assemblers. +branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a +KBUILD_CFLAGS += $(branch-prot-flags-y) +endif + ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) KBUILD_CPPFLAGS += -mbig-endian CHECKFLAGS += -D__AARCH64EB__ -- 2.7.4