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arm64: bti: Provide Kconfig for kernel mode BTI 

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>
Link: https://lore.kernel.org/r/20200506195138.22086-8-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Brown 2020-05-06 20:51:34 +01:00 committed by Will Deacon
parent 67d4a1cd09
commit 97fed779f2
1 changed files with 19 additions and 0 deletions
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arch/arm64/Kconfig
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@ -1610,6 +1610,25 @@ 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 !(CC_IS_CLANG && GCOV_KERNEL)
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