Re: [PATCH v9 13/13] arm64: BTI: Add Kconfig entry for userspace BTI

Kees Cook
2020-03-13T00:01:53Z

On Wed, Mar 11, 2020 at 07:26:08PM +0000, Mark Brown wrote:
> From: Dave Martin <Dave.Martin@arm.com>
>
> Now that the code for userspace BTI support is in the kernel add the
> Kconfig entry so that it can be built and used.
>
> [Split out of "arm64: Basic Branch Target Identification support" --
> broonie]
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/Kconfig | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 8a15bc68dadd..d65d226a77ec 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1522,6 +1522,28 @@ endmenu
>
> menu "ARMv8.5 architectural features"
>
> +config ARM64_BTI
> + bool "Branch Target Identification support"
> + default y
> + help
> + Branch Target Identification (part of the ARMv8.5 Extensions)
> + provides a mechanism to limit the set of locations to which computed
> + branch instructions such as BR or BLR can jump.
> +
> + To make use of BTI on CPUs that support it, say Y.
> +
> + BTI is intended to provide complementary protection to other control
> + flow integrity protection mechanisms, such as the Pointer
> + authentication mechanism provided as part of the ARMv8.3 Extensions.
> + For this reason, it does not make sense to enable this option without
> + also enabling support for pointer authentication. Thus, when
> + enabling this option you should also select ARM64_PTR_AUTH=y.
> +
> + Userspace binaries must also be specifically compiled to make use of
> + this mechanism. If you say N here or the hardware does not support
> + BTI, such binaries can still run, but you get no additional
> + enforcement of branch destinations.
> +
> config ARM64_E0PD
> bool "Enable support for E0PD"
> default y
> --
> 2.20.1
>

--
Kees Cook