{"id":69973,"date":"2025-09-11T22:32:18","date_gmt":"2025-09-11T19:02:18","guid":{"rendered":"https:\/\/afaghhosting.net\/blog\/cve-2025-40300-x86-vmscape-add-conditional-ibpb-mitigation\/"},"modified":"2025-09-11T22:32:18","modified_gmt":"2025-09-11T19:02:18","slug":"cve-2025-40300-x86-vmscape-add-conditional-ibpb-mitigation","status":"publish","type":"post","link":"https:\/\/afaghhosting.net\/blog\/cve-2025-40300-x86-vmscape-add-conditional-ibpb-mitigation\/","title":{"rendered":"CVE-2025-40300 &#8211; x86\/vmscape: Add conditional IBPB mitigation"},"content":{"rendered":"<p><strong>CVE ID : <\/strong>CVE-2025-40300<br \/>\n<br \/>\n<strong>Published : <\/strong> Sept. 11, 2025, 5:15 p.m. | 1\u00a0hour, 26\u00a0minutes ago<br \/>\n<br \/>\n<strong>Description : <\/strong>In the Linux kernel, the following vulnerability has been resolved:<\/p>\n<p>x86\/vmscape: Add conditional IBPB mitigation<\/p>\n<p>VMSCAPE is a vulnerability that exploits insufficient branch predictor<br \/>\nisolation between a guest and a userspace hypervisor (like QEMU). Existing<br \/>\nmitigations already protect kernel\/KVM from a malicious guest. Userspace<br \/>\ncan additionally be protected by flushing the branch predictors after a<br \/>\nVMexit.<\/p>\n<p>Since it is the userspace that consumes the poisoned branch predictors,<br \/>\nconditionally issue an IBPB after a VMexit and before returning to<br \/>\nuserspace. Workloads that frequently switch between hypervisor and<br \/>\nuserspace will incur the most overhead from the new IBPB.<\/p>\n<p>This new IBPB is not integrated with the existing IBPB sites. For<br \/>\ninstance, a task can use the existing speculation control prctl() to<br \/>\nget an IBPB at context switch time. With this implementation, the<br \/>\nIBPB is doubled up: one at context switch and another before running<br \/>\nuserspace.<\/p>\n<p>The intent is to integrate and optimize these cases post-embargo.<\/p>\n[ dhansen: elaborate on suboptimal IBPB solution ]\n<br \/>\n<strong>Severity:<\/strong> 0.0 | NA<br \/>\n<br \/>\nVisit the link for more details, such as CVSS details, affected products, timeline, and more&#8230;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>CVE ID : CVE-2025-40300 Published : Sept. 11, 2025, 5:15 p.m. | 1\u00a0hour, 26\u00a0minutes ago Description : In the Linux kernel, the following vulnerability has been resolved: x86\/vmscape: Add conditional IBPB mitigation VMSCAPE is a vulnerability that exploits insufficient branch predictor isolation between a guest and a userspace hypervisor (like QEMU). Existing mitigations already protect &hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-69973","post","type-post","status-publish","format-standard","hentry","category-vulnerability"],"_links":{"self":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/69973","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/comments?post=69973"}],"version-history":[{"count":0,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/69973\/revisions"}],"wp:attachment":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/media?parent=69973"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/categories?post=69973"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/tags?post=69973"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}