[PATCH v3 07/11] arm64: bti: Provide Kconfig for kernel mode BTI

Mark Brown
2020-05-06T19:53:54Z

Now that all the code is in place provide a Kconfig option allowing users
to enable BTI for the kernel if their toolchain supports it, defaulting it
on since this has security benefits. This is a separate configuration
option since we currently don't support secondary CPUs that lack BTI if
the boot CPU supports it.

Code generation issues mean that current GCC 9 versions are not able to
produce usable BTI binaries so we disable support for building with GCC
versions prior to 10, once a fix is backported to GCC 9 the dependencies
will be updated.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/Kconfig | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6f199d8146d4..f3de1c115fc0 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1610,6 +1610,24 @@ config ARM64_BTI
BTI, such binaries can still run, but you get no additional
enforcement of branch destinations.

+config ARM64_BTI_KERNEL
+ bool "Use Branch Target Identification for kernel"
+ default y
+ depends on ARM64_BTI
+ depends on ARM64_PTR_AUTH
+ depends on CC_HAS_BRANCH_PROT_PAC_RET_BTI
+ depends on !CC_IS_GCC || GCC_VERSION >= 100000
+ depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
+ help
+ Build the kernel with Branch Target Identification annotations
+ and enable enforcement of this for kernel code. When this option
+ is enabled and the system supports BTI all kernel code including
+ modular code must have BTI enabled.
+
+config CC_HAS_BRANCH_PROT_PAC_RET_BTI
+ # GCC 9 or later, clang 8 or later
+ def_bool $(cc-option,-mbranch-protection=pac-ret+leaf+bti)
+
config ARM64_E0PD
bool "Enable support for E0PD"
default y
--
2.20.1