linux-kernel - [PATCH] KVM: s390: Do not leak kernel stack data in the KVM_S390

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Message-Id: <20190912090050.20295-1-thuth@redhat.com>
Date:   Thu, 12 Sep 2019 11:00:50 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: s390: Do not leak kernel stack data in the KVM_S390_INTERRUPT ioctl

When the userspace program runs the KVM_S390_INTERRUPT ioctl to inject
an interrupt, we convert them from the legacy struct kvm_s390_interrupt
to the new struct kvm_s390_irq via the s390int_to_s390irq() function.
However, this function does not take care of all types of interrupts
that we can inject into the guest later (see do_inject_vcpu()). Since we
do not clear out the s390irq values before calling s390int_to_s390irq(),
there is a chance that we copy unwanted data from the kernel stack
into the guest memory later if the interrupt data has not been properly
initialized by s390int_to_s390irq().

Specifically, the problem exists with the KVM_S390_INT_PFAULT_INIT
interrupt: s390int_to_s390irq() does not handle it, but the function
__deliver_pfault_init() will later copy the uninitialized stack data
from the ext.ext_params2 into the guest memory.

Fix it by handling that interrupt type in s390int_to_s390irq(), too.
And while we're at it, make sure that s390int_to_s390irq() now
directly returns -EINVAL for unknown interrupt types, so that we
do not run into this problem again in case we add more interrupt
types to do_inject_vcpu() sometime in the future.

Signed-off-by: Thomas Huth <thuth@...hat.com>
---
 arch/s390/kvm/interrupt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 3e7efdd9228a..165dea4c7f19 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1960,6 +1960,16 @@ int s390int_to_s390irq(struct kvm_s390_interrupt *s390int,
 	case KVM_S390_MCHK:
 		irq->u.mchk.mcic = s390int->parm64;
 		break;
+	case KVM_S390_INT_PFAULT_INIT:
+		irq->u.ext.ext_params = s390int->parm;
+		irq->u.ext.ext_params2 = s390int->parm64;
+		break;
+	case KVM_S390_RESTART:
+	case KVM_S390_INT_CLOCK_COMP:
+	case KVM_S390_INT_CPU_TIMER:
+		break;
+	default:
+		return -EINVAL;
 	}
 	return 0;
 }
-- 
2.18.1