On 05/22/2018 08:06 AM, Marc Zyngier wrote:
> On a system where the firmware implements ARCH_WORKAROUND_2,
> it may be useful to either permanently enable or disable the
> workaround for cases where the user decides that they'd rather
> not get a trap overhead, and keep the mitigation permanently
> on or off instead of switching it on exception entry/exit.
>
> In any case, default to the mitigation being enabled.
>
> Signed-off-by: Marc Zyngier <marc.zyng...@arm.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 17 ++++
> arch/arm64/include/asm/cpufeature.h | 6 ++
> arch/arm64/kernel/cpu_errata.c | 102
> ++++++++++++++++++++----
> 3 files changed, 109 insertions(+), 16 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index f2040d46f095..646e112c6f63 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4092,6 +4092,23 @@
> expediting. Set to zero to disable automatic
> expediting.
>
> + ssbd= [ARM64,HW]
> + Speculative Store Bypass Disable control
> +
> + On CPUs that are vulnerable to the Speculative
> + Store Bypass vulnerability and offer a
> + firmware based mitigation, this parameter
> + indicates how the mitigation should be used:
> +
> + force-on: Unconditionnaly enable mitigation for
Unconditionally
> + for both kernel and userspace
> + force-off: Unconditionnaly disable mitigation for
Unconditionally
> + for both kernel and userspace
> + kernel: Always enable mitigation in the
> + kernel, and offer a prctl interface
> + to allow userspace to register its
> + interest in being mitigated too.
> +
> stack_guard_gap= [MM]
> override the default stack gap protection. The value
> is in page units and it defines how many pages prior
--
~Randy
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