Bug 2507123 (CVE-2026-64286)

Summary: CVE-2026-64286 kernel: KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) for arm64 architecture. The `flush_hyp_vcpu()` function, responsible for copying the host virtual CPU (vCPU) context, does not properly clear a specific internal pointer (`__hyp_running_vcpu`). This oversight allows a host to provide a value that is then improperly accessed (dereferenced) at Exception Level 2 (EL2), potentially leading to arbitrary memory access within the hypervisor. This could allow a malicious host to compromise the integrity or availability of the hypervisor.
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Description OSIDB Bzimport 2026-07-25 10:06:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU

flush_hyp_vcpu() copies the host vCPU context into the hyp's private
vCPU on every run. ctxt_to_vcpu() expects a guest context to have a
NULL __hyp_running_vcpu, which is only ever set on the host context, so
that it resolves the vCPU via container_of(). While this is generally
the case, flush_hyp_vcpu() copies the context verbatim and does not
enforce this, so a value provided by the host is dereferenced at EL2
(host -> EL2).

Fix by clearing __hyp_running_vcpu after the copy.
Comment 1 TEJ RATHI 2026-07-30 03:29:05 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072503-CVE-2026-64286-3ed3@gregkh/T