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KVM: s390: mark irq_state.flags as non-usable 

Old kernels did not check for zero in the irq_state.flags field and old
QEMUs did not zero the flag/reserved fields when calling
KVM_S390_*_IRQ_STATE.  Let's add comments to prevent future uses of
these fields.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
Christian Borntraeger 2017-11-21 16:02:52 +01:00
parent 940f89a5a3
commit bb64da9aba
3 changed files with 18 additions and 7 deletions
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15
Documentation/virtual/kvm/api.txt
View File

@ -2901,14 +2901,19 @@ userspace buffer and its length:
struct kvm_s390_irq_state {
__u64 buf;
__u32 flags;
__u32 flags; /* will stay unused for compatibility reasons */
__u32 len;
__u32 reserved[4];
__u32 reserved[4]; /* will stay unused for compatibility reasons */
};
Userspace passes in the above struct and for each pending interrupt a
struct kvm_s390_irq is copied to the provided buffer.
The structure contains a flags and a reserved field for future extensions. As
the kernel never checked for flags == 0 and QEMU never pre-zeroed flags and
reserved, these fields can not be used in the future without breaking
compatibility.
If -ENOBUFS is returned the buffer provided was too small and userspace
may retry with a bigger buffer.
@ -2932,10 +2937,14 @@ containing a struct kvm_s390_irq_state:
struct kvm_s390_irq_state {
__u64 buf;
__u32 flags; /* will stay unused for compatibility reasons */
__u32 len;
__u32 pad;
__u32 reserved[4]; /* will stay unused for compatibility reasons */
};
The restrictions for flags and reserved apply as well.
(see KVM_S390_GET_IRQ_STATE)
The userspace memory referenced by buf contains a struct kvm_s390_irq
for each interrupt to be injected into the guest.
If one of the interrupts could not be injected for some reason the

6
arch/s390/kvm/kvm-s390.c
View File

@ -1,8 +1,8 @@
// SPDX-License-Identifier: GPL-2.0
/*
* hosting zSeries kernel virtual machines
* hosting IBM Z kernel virtual machines (s390x)
*
* Copyright IBM Corp. 2008, 2009
* Copyright IBM Corp. 2008, 2017
*
* Author(s): Carsten Otte <cotte@de.ibm.com>
* Christian Borntraeger <borntraeger@de.ibm.com>
@ -3808,6 +3808,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = -EINVAL;
break;
}
/* do not use irq_state.flags, it will break old QEMUs */
r = kvm_s390_set_irq_state(vcpu,
(void __user *) irq_state.buf,
irq_state.len);
@ -3823,6 +3824,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = -EINVAL;
break;
}
/* do not use irq_state.flags, it will break old QEMUs */
r = kvm_s390_get_irq_state(vcpu,
(__u8 __user *) irq_state.buf,
irq_state.len);

4
include/uapi/linux/kvm.h
View File

@ -630,9 +630,9 @@ struct kvm_s390_irq {
struct kvm_s390_irq_state {
__u64 buf;
__u32 flags;
__u32 flags; /* will stay unused for compatibility reasons */
__u32 len;
__u32 reserved[4];
__u32 reserved[4]; /* will stay unused for compatibility reasons */
};
/* for KVM_SET_GUEST_DEBUG */