[PATCH v10 02/40] prctl: arch-agnostic prctl for shadow stack

[Catalin Marinas]

On Thu, Aug 01, 2024 at 01:06:29PM +0100, Mark Brown wrote:
> Three architectures (x86, aarch64, riscv) have announced support for
> shadow stacks with fairly similar functionality.  While x86 is using
> arch_prctl() to control the functionality neither arm64 nor riscv uses
> that interface so this patch adds arch-agnostic prctl() support to
> get and set status of shadow stacks and lock the current configuation to
> prevent further changes, with support for turning on and off individual
> subfeatures so applications can limit their exposure to features that
> they do not need.  The features are:
> 
>   - PR_SHADOW_STACK_ENABLE: Tracking and enforcement of shadow stacks,
>     including allocation of a shadow stack if one is not already
>     allocated.
>   - PR_SHADOW_STACK_WRITE: Writes to specific addresses in the shadow
>     stack.
>   - PR_SHADOW_STACK_PUSH: Push additional values onto the shadow stack.
> 
> These features are expected to be inherited by new threads and cleared
> on exec(), unknown features should be rejected for enable but accepted
> for locking (in order to allow for future proofing).
> 
> This is based on a patch originally written by Deepak Gupta but modified
> fairly heavily, support for indirect landing pads is removed, additional
> modes added and the locking interface reworked.  The set status prctl()
> is also reworked to just set flags, if setting/reading the shadow stack
> pointer is required this could be a separate prctl.
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann at linaro.org>
> Signed-off-by: Mark Brown <broonie at kernel.org>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>