Re: [PATCH v3 3/6] KVM: arm64: Ignore HCR_EL2.FIEN set by L1 guest's EL2

[Joey Gouly <joey.gouly@arm.com>]

On Sun, Aug 17, 2025 at 09:21:55PM +0100, Marc Zyngier wrote:
> An EL2 guest can set HCR_EL2.FIEN, which gives access to the RASv1p1
> fault injection mechanism. This would allow an EL1 guest to inject
> error records into the system, which does sound like a terrible idea.
> 
> Prevent this situation by added FIEN to the list of bits we silently
> exclude from being inserted into the host configuration.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Reviewed-by: Joey Gouly <joey.gouly@arm.com>

> ---
>  arch/arm64/kvm/hyp/vhe/switch.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> index e482181c66322..0998ad4a25524 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -43,8 +43,11 @@ DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);
>   *
>   * - API/APK: they are already accounted for by vcpu_load(), and can
>   *   only take effect across a load/put cycle (such as ERET)
> + *
> + * - FIEN: no way we let a guest have access to the RAS "Common Fault
> + *   Injection" thing, whatever that does
>   */
> -#define NV_HCR_GUEST_EXCLUDE	(HCR_TGE | HCR_API | HCR_APK)
> +#define NV_HCR_GUEST_EXCLUDE	(HCR_TGE | HCR_API | HCR_APK | HCR_FIEN)
>  
>  static u64 __compute_hcr(struct kvm_vcpu *vcpu)
>  {
> -- 
> 2.39.2
>