linux-kernel - Re: [PATCH v3 1/4] KVM: s390: vsie: Fix STFLE interpretive execution identification

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Message-ID: <b31db584-89bf-4c42-bff9-b6388dcd9edc@linux.ibm.com>
Date:   Mon, 4 Dec 2023 16:24:12 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Nina Schoetterl-Glausch <nsg@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Sven Schnelle <svens@...ux.ibm.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3 1/4] KVM: s390: vsie: Fix STFLE interpretive execution
 identification

On 11/8/23 18:12, Nina Schoetterl-Glausch wrote:
> 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@...ux.ibm.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
> ---
>   arch/s390/kvm/vsie.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 61499293c2ac..d989772fe211 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -988,9 +988,10 @@ 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)) {
> +		fac = fac & 0x7ffffff8U;

Switch the retry and the facility assignment.
Add the following comment:

Facility list origin (FLO) is in bits 1 - 28 of the FLD so we need to 
mask here before reading.


Apart from that this looks fine to me.


>   		retry_vsie_icpt(vsie_page);
>   		if (read_guest_real(vcpu, fac, &vsie_page->fac,
>   				    sizeof(vsie_page->fac)))