Re: [PATCH v6 07/13] KVM: s390: introduce struct kvm_s390_gisa_interrupt

From: Michael Mueller
Date: Tue Jan 29 2019 - 10:47:19 EST

On 29.01.19 14:22, Cornelia Huck wrote:
On Mon, 28 Jan 2019 17:50:54 +0100
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:

On Thu, 24 Jan 2019 13:59:33 +0100
Michael Mueller <mimu@xxxxxxxxxxxxx> wrote:

Use this struct analog to the kvm interruption structs
for kvm emulated floating and local interruptions.
Further fields will be added with this series as

Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>

While looking at this I was asking myself what guards against invalid
gisa pointer dereference e.g. when pending_irqs() is called (see below).

AFAIU we set up gisa_int.origin only if we have
css_general_characteristics.aiv. Opinions?

I think you're right that this is a (pre-existing) problem.

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 942cc7d33766..ee91d1de0036 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -246,7 +246,8 @@ static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu *vcpu)
static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
return pending_irqs_no_gisa(vcpu) |
- gisa_get_ipm(vcpu->kvm->arch.gisa) << IRQ_PEND_IO_ISC_7;
+ gisa_get_ipm(vcpu->kvm->arch.gisa_int.origin) <<

Unconditional call to gisa_get_ipm(), and get ipm just accesses ->ipm.

All other callers of this function check for gisa != NULL first, so
either we should check here as well or move the check into the
gisa_get_ipm() function.

I suggest to use an explicit test like this.

static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
- return pending_irqs_no_gisa(vcpu) |
- gisa_get_ipm(vcpu->kvm->arch.gisa_int.origin) <<
+ struct kvm_s390_gisa_int *gi = &vcpu->kvm->arch.gisa_int;
+ unsigned long pending_mask;
+ pending_mask = pending_irqs_no_gisa(vcpu);
+ if (gi->origin)
+ pending_mask |= gisa_get_ipm(gi->origin) << IRQ_PEND_IO_ISC_7;
+ return pending_mask;