In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN<\/p>\n
Don’t reset the VMCB’s TLB control back to “do nothing” on a failed VMRUN,
\nas empirical testing shows that the CPU performs the requested TLB flush if
\nand only if VMRUN is successful, i.e. clearing TLB control on a failed
\nVMRUN effectively drops a TLB flush.<\/p>\n
Explicitly track the need to flush all ASIDs on a per-CPU basis, as the
\nASID reuse condition is tied to the pCPU, not to the vCPU. As a bonus,
\nthis also obviates the need to avoid clobbering FLUSH_ALL_ASID with
\nTLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().<\/p>\n
Deliberately don’t bother saving\/restoring the “old” tlb_ctl on failure,
\nin quotes because it’s not exactly the old tlb_ctl, it’s the tlb_ctl from
\nafter pre_svm_run(), but before updating tlb_ctl for flush_all_asids. If
\nVMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next
\nsuccessful run of the VMCB *may* unnecessarily flush all ASIDs, which
\nstrictly speaking could result in noisy neighbor issues. However, the
\nfact that new_asid() is already guest-triggerable, because of KVM’s flawed
\nbehavior of clearing the ASID on emulated INIT, means that a guest can
\nalready trigger a flush of all ASIDs at roughly the same rate. And once
\nKVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID
\nto each vCPU, this flaw goes away.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN<\/p>\n
Don’t reset the VMCB’s TLB control back to “do nothing” on<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-41187","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/41187","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=41187"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=41187"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=41187"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}