Bug 1683956 (CVE-2019-17348)

Summary: CVE-2019-17348 xen: xsa294: Insufficient TLB flushing when using PCID
Product: [Other] Security Response Reporter: Andrej Nemec <anemec>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED WONTFIX QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: ailan, drjones, imammedo, jforbes, knoel, m.a.young, mrezanin, pbonzini, rkrcmar, robinlee.sysu, security-response-team, vkuznets, xen-maint
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Fixed In Version: Doc Type: If docs needed, set a value
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Clone Of: Environment:
Last Closed: 2019-06-10 10:49:06 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 1685577    
Bug Blocks:    

Description Andrej Nemec 2019-02-28 08:11:47 UTC
Use of Process Context Identifiers (PCID) was introduced into Xen in
order to improve performance after XSA-254 (and in particular its
Meltdown sub-issue).  This enablement implied changes to the TLB
flushing logic.  One aspect which was overlooked is the safety of
switching between shadow pagetables, which previously relied on the
unconditional flushing of a write to CR3.

With PCID enabled, a switch of shadow pagetable for a 64bit PV guest
fails to invalidate the linear mappings of the previous shadow
pagetable.  As a result, subsequent accesses to the shadow pagetables
may be deemed to be safe by the shadow logic (based on the old shadow
pagetable) but fault when made in practice.

Comment 1 Andrej Nemec 2019-03-05 14:23:26 UTC


Comment 2 Andrej Nemec 2019-03-05 14:26:15 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1685577]