On Mon, Feb 10, 2025 at 06:41:37PM +0000, Marc Zyngier wrote:
> We don't seem to be handling the GCS-specific exception class.
> Handle it by delivering an UNDEF to the guest, and populate the
> relevant trap bits.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kvm/handle_exit.c | 11 +++++++++++
> arch/arm64/kvm/sys_regs.c | 8 ++++++++
> 2 files changed, 19 insertions(+)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 4f8354bf7dc5f..624a78a99e38a 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -294,6 +294,16 @@ static int handle_svc(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static int kvm_handle_gcs(struct kvm_vcpu *vcpu)
> +{
> + /* We don't expect GCS, so treat it with contempt */
> + if (kvm_has_feat(vcpu->kvm, ID_AA64PFR1_EL1, GCS, IMP))
> + WARN_ON_ONCE(1);
Just to check / better my understanging, do we enforce that this can't
be exposed to the guest somewhere?
I see __kvm_read_sanitised_id_reg() masks it out, and the sys_reg_descs
table has it filtered, but I'm not immediately sure whether that
prevents host userspace maliciously setting this?
Otherwise this looks good to me.
Mark.
> +
> + kvm_inject_undefined(vcpu);
> + return 1;
> +}
> +
> static int handle_ls64b(struct kvm_vcpu *vcpu)
> {
> struct kvm *kvm = vcpu->kvm;
> @@ -384,6 +394,7 @@ static exit_handle_fn arm_exit_handlers[] = {
> [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug,
> [ESR_ELx_EC_FP_ASIMD] = kvm_handle_fpasimd,
> [ESR_ELx_EC_PAC] = kvm_handle_ptrauth,
> + [ESR_ELx_EC_GCS] = kvm_handle_gcs,
> };
>
> static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 18721c773475d..2ecd0d51a2dae 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -5056,6 +5056,14 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
> HFGITR_EL2_nBRBIALL);
> }
>
> + if (!kvm_has_feat(kvm, ID_AA64PFR1_EL1, GCS, IMP)) {
> + kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> + HFGxTR_EL2_nGCS_EL1);
> + kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_nGCSPUSHM_EL1 |
> + HFGITR_EL2_nGCSSTR_EL1 |
> + HFGITR_EL2_nGCSEPP);
> + }
> +
> set_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags);
> out:
> mutex_unlock(&kvm->arch.config_lock);
> --
> 2.39.2
>
