From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:56750 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932487AbbLGOh7 (ORCPT ); Mon, 7 Dec 2015 09:37:59 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christian Borntraeger , David Hildenbrand Subject: [PATCH 4.1 67/95] KVM: s390: SCA must not cross page boundaries Date: Mon, 7 Dec 2015 09:36:01 -0500 Message-Id: <20151207142742.556786043@linuxfoundation.org> In-Reply-To: <20151207142739.317088107@linuxfoundation.org> References: <20151207142739.317088107@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: stable-owner@vger.kernel.org List-ID: 4.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Hildenbrand commit c5c2c393468576bad6d10b2b5fefff8cd25df3f4 upstream. We seemed to have missed a few corner cases in commit f6c137ff00a4 ("KVM: s390: randomize sca address"). The SCA has a maximum size of 2112 bytes. By setting the sca_offset to some unlucky numbers, we exceed the page. 0x7c0 (1984) -> Fits exactly 0x7d0 (2000) -> 16 bytes out 0x7e0 (2016) -> 32 bytes out 0x7f0 (2032) -> 48 bytes out One VCPU entry is 32 bytes long. For the last two cases, we actually write data to the other page. 1. The address of the VCPU. 2. Injection/delivery/clearing of SIGP externall calls via SIGP IF. Especially the 2. happens regularly. So this could produce two problems: 1. The guest losing/getting external calls. 2. Random memory overwrites in the host. So this problem happens on every 127 + 128 created VM with 64 VCPUs. Acked-by: Christian Borntraeger Signed-off-by: David Hildenbrand Signed-off-by: Christian Borntraeger Signed-off-by: Greg Kroah-Hartman --- arch/s390/kvm/kvm-s390.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -1031,7 +1031,9 @@ int kvm_arch_init_vm(struct kvm *kvm, un if (!kvm->arch.sca) goto out_err; spin_lock(&kvm_lock); - sca_offset = (sca_offset + 16) & 0x7f0; + sca_offset += 16; + if (sca_offset + sizeof(struct sca_block) > PAGE_SIZE) + sca_offset = 0; kvm->arch.sca = (struct sca_block *) ((char *) kvm->arch.sca + sca_offset); spin_unlock(&kvm_lock);