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

Halil Pasic
2019-01-28T16:50:54Z

On Thu, 24 Jan 2019 13:59:33 +0100
Michael Mueller <mimu@linux.ibm.com> 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
> required.
>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>

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?

Anyway if it is a problem, it is a pre-existing one (should be fixed
ASAP but does not affect the validity of this patch).

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

> ---
> arch/s390/include/asm/kvm_host.h | 6 ++++-
> arch/s390/kvm/interrupt.c | 52 +++++++++++++++++++++++-----------------
> arch/s390/kvm/kvm-s390.c | 2 +-
> 3 files changed, 36 insertions(+), 24 deletions(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index c259a67c4298..0941571d34eb 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -803,6 +803,10 @@ struct kvm_s390_vsie {
> struct page *pages[KVM_MAX_VCPUS];
> };
>

[..]

> 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.

> + IRQ_PEND_IO_ISC_7;
> }
>

[..]

> void kvm_s390_gisa_init(struct kvm *kvm)
> {
> + struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> +
> if (!css_general_characteristics.aiv)
> return;
> - kvm->arch.gisa = &kvm->arch.sie_page2->gisa;
> + gi->origin = &kvm->arch.sie_page2->gisa;

Should stay NULL if !css_general_characteristics.aiv.

> kvm_s390_gisa_clear(kvm);
> - VM_EVENT(kvm, 3, "gisa 0x%pK initialized", kvm->arch.gisa);
> + VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
> }
>