Date: Tue, 10 Dec 2019 12:09:22 -0600 From: Tyler Hicks <tyhicks@...onical.com> To: oss-security@...ts.openwall.com Subject: Re: CVE-2019-19338 Kernel: KVM: export MSR_IA32_TSX_CTRL to guest - incomplete fix for TAA (CVE-2019-11135) On 2019-12-10 17:10:40, P J P wrote: > Hello, Hello! > Transaction Asynchronous Abort (TAA) h/w issue, which affects Intel CPUs, is > mitigated in two ways. One is by disabling Transactional Synchronisation > Extensions (TSX) feature of the CPU. And second is by clearing the affected > Store/Fill/Load port architectural buffers, which may hold sensitive > information bits. > > It was found that the current kernel fixes don't completely fix TAA issue > for guest VMs. When a guest is running on a host CPU affected by TAA (ie. > TAA_NO=0) but not affected by MDS issue (ie MDS_NO=1), to mitigate TAA > issue, guest was to clear the affected buffers by using VERW instruction > mechanism. But when MDS_NO=1 bit was exported to the guests, it did not > quite use the VERW mechanism to clear the affected buffers. > > This issue affects guests running on Cascade Lake CPUs, which are affected > by the TAA (ie. TAA_NO=0) issue, but are not affected by the MDS (ie. > MDS_NO=1) issue. > > It requires that host has 'TSX' enabled. > > Upstream patches: > ----------------- > -> https://git.kernel.org/linus/cbbaa2727aa3ae9e0a844803da7cef7fd3b94f2b > -> https://git.kernel.org/linus/c11f83e0626bdc2b6c550fc8b9b6eeefbd8cefaa > -> https://git.kernel.org/linus/b07a5c53d42a8c87b208614129e947dd2338ff9c > > Another option: Export MDS_NO=0 to guests when TSX is enabled > -> https://git.kernel.org/linus/e1d38b63acd843cfdd4222bf19a26700fd5c699e If this commit, which was part of the initial set of mitigation patches for TAA, is a valid option then I'm not understanding how there was an incomplete fix. Is the CVE assignment specifically for a distro kernel that didn't include commit e1d38b63acd8 ("kvm/x86: Export MDS_NO=0 to guests when TSX is enabled")? Tyler > > 'CVE-2019-19338' is assigned by Red Hat Inc. > > Thank you. > -- > Prasad J Pandit / Red Hat Product Security Team > 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D >
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