On Thu, 29 Aug 2019 12:53:56 +0200 Thomas Huth <thuth@xxxxxxxxxx> wrote: > If the KVM_S390_MEM_OP ioctl is called with an access register >= 16, > then there is certainly a bug in the calling userspace application. > We check for wrong access registers, but only if the vCPU was already > in the access register mode before (i.e. the SIE block has recorded > it). The check is also buried somewhere deep in the calling chain (in > the function ar_translation()), so this is somewhat hard to find. > > It's better to always report an error to the userspace in case this > field is set wrong, and it's safer in the KVM code if we block wrong > values here early instead of relying on a check somewhere deep down > the calling chain, so let's add another check to kvm_s390_guest_mem_op() > directly. > > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx> > --- > arch/s390/kvm/kvm-s390.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index f329dcb3f44c..725690853cbd 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -4255,7 +4255,7 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu, > const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION > | KVM_S390_MEMOP_F_CHECK_ONLY; > > - if (mop->flags & ~supported_flags) > + if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS) > return -EINVAL; This also matches the value that ar_translation would return, so seems sane. > > if (mop->size > MEM_OP_MAX_SIZE) Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx> Btw: should Documentation/virt/kvm/api.txt spell out the valid range for ar explicitly?
