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    Subject[PATCH 34/45] KVM: s390: Sanity check on validity intercept
    Date
    From: Carsten Otte <cotte@de.ibm.com>

    This patch adds a sanity check for the content of the guest
    prefix register content before faulting in the cpu lowcore
    that it refers to. The guest might end up in an endless loop
    where SIE complains about missing lowcore with incorrect
    content of the prefix register without this fix.

    Reported-by: Mijo Safradin <mijo@linux.vnet.ibm.com>
    Signed-off-by: Carsten Otte <cotte@de.ibm.com>
    Signed-off-by: Christian Ehrhardt <ehrhardt@de.ibm.com>
    Signed-off-by: Avi Kivity <avi@redhat.com>
    ---
    arch/s390/kvm/intercept.c | 28 ++++++++++++++++++----------
    1 files changed, 18 insertions(+), 10 deletions(-)

    diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
    index 9d19803..98997cc 100644
    --- a/arch/s390/kvm/intercept.c
    +++ b/arch/s390/kvm/intercept.c
    @@ -154,17 +154,25 @@ static int handle_stop(struct kvm_vcpu *vcpu)
    static int handle_validity(struct kvm_vcpu *vcpu)
    {
    int viwhy = vcpu->arch.sie_block->ipb >> 16;
    + int rc;
    +
    vcpu->stat.exit_validity++;
    - if (viwhy == 0x37) {
    - fault_in_pages_writeable((char __user *)
    - vcpu->kvm->arch.guest_origin +
    - vcpu->arch.sie_block->prefix,
    - PAGE_SIZE);
    - return 0;
    - }
    - VCPU_EVENT(vcpu, 2, "unhandled validity intercept code %d",
    - viwhy);
    - return -ENOTSUPP;
    + if ((viwhy == 0x37) && (vcpu->arch.sie_block->prefix
    + <= vcpu->kvm->arch.guest_memsize - 2*PAGE_SIZE)){
    + rc = fault_in_pages_writeable((char __user *)
    + vcpu->kvm->arch.guest_origin +
    + vcpu->arch.sie_block->prefix,
    + 2*PAGE_SIZE);
    + if (rc)
    + /* user will receive sigsegv, exit to user */
    + rc = -ENOTSUPP;
    + } else
    + rc = -ENOTSUPP;
    +
    + if (rc)
    + VCPU_EVENT(vcpu, 2, "unhandled validity intercept code %d",
    + viwhy);
    + return rc;
    }

    static int handle_instruction(struct kvm_vcpu *vcpu)
    --
    1.6.0.6


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