Bug 2511944 (CVE-2026-64604)

Summary: CVE-2026-64604 kernel: KVM: VMX: Grab vmcs12 on CR8 interception update iff vCPU is in guest mode
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) component. This vulnerability involves how KVM handles virtual machine control structures (VMCS) during certain operations within a virtual machine. An attacker with local access to a virtual machine could exploit this flaw to trigger a system warning, potentially causing the host system to become unstable or unavailable, leading to a denial of service (DoS).
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-08-06 07:32:09 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: VMX: Grab vmcs12 on CR8 interception update iff vCPU is in guest mode

When updating CR8 intercepts, get vmcs12 if and only if the vCPU is in
guest mode so that a future change can have update CR8 intercepts during
vCPU creation, without running afoul of get_vmcs12()'s lockdep assertion.

  ------------[ cut here ]------------
  debug_locks && !(lock_is_held(&(&vcpu->mutex)->dep_map) || !refcount_read(&vcpu->kvm->users_count))
  WARNING: arch/x86/kvm/vmx/nested.h:61 at get_vmcs12 arch/x86/kvm/vmx/nested.h:60 [inline], CPU#0: syz.2.19/5879
  WARNING: arch/x86/kvm/vmx/nested.h:61 at vmx_update_cr8_intercept+0x3de/0x4e0 arch/x86/kvm/vmx/vmx.c:6879, CPU#0: syz.2.19/5879
  Modules linked in:
  CPU: 0 UID: 0 PID: 5879 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
  RIP: 0010:get_vmcs12 arch/x86/kvm/vmx/nested.h:60 [inline]
  RIP: 0010:vmx_update_cr8_intercept+0x3de/0x4e0 arch/x86/kvm/vmx/vmx.c:6879
  Call Trace:
   <TASK>
   apic_update_ppr arch/x86/kvm/lapic.c:984 [inline]
   kvm_lapic_reset+0x1c24/0x2980 arch/x86/kvm/lapic.c:3023
   kvm_vcpu_reset+0x44c/0x1bf0 arch/x86/kvm/x86.c:12986
   kvm_arch_vcpu_create+0x746/0x8b0 arch/x86/kvm/x86.c:12847
   kvm_vm_ioctl_create_vcpu+0x428/0x930 virt/kvm/kvm_main.c:4201
   kvm_vm_ioctl+0x893/0xd50 virt/kvm/kvm_main.c:5159
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:597 [inline]
   __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

No functional change intended.
Comment 1 Mauro Matteo Cascella 2026-08-06 17:41:26 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026080653-CVE-2026-64604-8fea@gregkh/T