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CVE-2019-19338

Description

A flaw was found in the fix for CVE-2019-11135, in the Linux upstream kernel versions before 5.5 where, the way Intel CPUs handle speculative execution of instructions when a TSX Asynchronous Abort (TAA) error occurs. When a guest is running on a host CPU affected by the TAA flaw (TAA_NO=0), but is not affected by the MDS issue (MDS_NO=1), the guest was to clear the affected buffers by using a VERW instruction mechanism. But when the MDS_NO=1 bit was exported to the guests, the guests did not use the VERW mechanism to clear the affected buffers. This issue affects guests running on Cascade Lake CPUs and requires that host has 'TSX' enabled. Confidentiality of data is the highest threat associated with this vulnerability. #### Notes Author| Note ---|--- [tyhicks](<https://launchpad.net/~tyhicks>) | This is a vendor specific CVE for kernels that did not include upstream commit e1d38b63acd8 ("kvm/x86: Export MDS_NO=0 to guests when TSX is enabled") and defaulted to leaving TSX enabled. Ubuntu kernels included that commit and disabled TSX where possible as part of the initial TAA mitigations (CVE-2019-11135).


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