Re: [PATCH v4 1/4] KVM: s390: vsie: Fix STFLE interpretive execution identification

[Christian Borntraeger]

Am 19.12.23 um 15:08 schrieb Nina Schoetterl-Glausch:
> STFLE can be interpretively executed.
> This occurs when the facility list designation is unequal to zero.
> Perform the check before applying the address mask instead of after.
>
> Fixes: 66b630d5b7f2 ("KVM: s390: vsie: support STFLE interpretation")
> Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Nina Schoetterl-Glausch <nsg@xxxxxxxxxxxxx>

Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>

this should not matter in reality but maybe some weird guests puts this at address 0.
Do we want a unit test for that case?

> ---
>   arch/s390/kvm/vsie.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 8207a892bbe2..35937911724e 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -984,10 +984,15 @@ static void retry_vsie_icpt(struct vsie_page *vsie_page)
>   static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   {
>   	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
> -	__u32 fac = READ_ONCE(vsie_page->scb_o->fac) & 0x7ffffff8U;
> +	__u32 fac = READ_ONCE(vsie_page->scb_o->fac);
>   
>   	if (fac && test_kvm_facility(vcpu->kvm, 7)) {
>   		retry_vsie_icpt(vsie_page);
> +		/*
> +		 * The facility list origin (FLO) is in bits 1 - 28 of the FLD
> +		 * so we need to mask here before reading.
> +		 */
> +		fac = fac & 0x7ffffff8U;
>   		if (read_guest_real(vcpu, fac, &vsie_page->fac,
>   				    sizeof(vsie_page->fac)))
>   			return set_validity_icpt(scb_s, 0x1090U);