CVE-2026-99176KVM: nVMX: Reset MMU back to the root MMU if loading L2 state fails for !VM-Entry

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: nVMX: Reset MMU back to the root MMU if loading L2 state fails for !VM-Entry Reset the vCPU's MMU pointer back to the root MMU if loading L2 state fails in the "not from VM-Entry" case, i.e. when emulating RSM or handling KVM_SET_NESTED_STATE. Failure to unwind the MMU pointer results in KVM trying to run L1 with a nested MMU, and is especially problematic if the vCPU manages to free its nested state before the VM crashes. Constructing the root for a nested EPT MMU goes through vmcs12, which is dynamically allocated/freed when nVMX is enabled/disabled. And so if the nested state is freed with the MMU still pointing at the nested MMU, KVM will hit a NULL pointer deref when attempting to get L1=>L2 EPTP. BUG: kernel NULL pointer dereference, address: 0000000000000078 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 114a2d067 P4D 111743067 PUD 11141f067 PMD 0 Oops: Oops: 0000 [#1] SMP CPU: 20 UID: 1000 PID: 1272 Comm: nested_tdp_faul Not tainted 7.3.0-rc4-8c89f11d1a99b-sink-vm #1914 PREEMPTLAZY Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:nested_ept_get_eptp+0xb/0x10 [kvm_intel] Call Trace: <TASK> kvm_mmu_load+0xcd/0x870 [kvm] kvm_arch_vcpu_ioctl_run+0x18f5/0x1f80 [kvm] kvm_vcpu_ioctl+0x2c7/0x970 [kvm] __x64_sys_ioctl+0x90/0xd0 do_syscall_64+0x9c/0x4d0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x47491b </TASK> Modules linked in: kvm_intel kvm irqbypass CR2: 0000000000000078 ---[ end trace 0000000000000000 ]--- RIP: 0010:nested_ept_get_eptp+0xb/0x10 [kvm_intel] [sean: write changelog]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c2586874605ec23b611c57fe71d183d98f168971
• https://git.kernel.org/stable/c/c611337aee17a0627e365e58e2b6e78803fb3c36
• https://git.kernel.org/stable/c/df4d01be5b318024bec68654c7af0ebc0e0ed8a1
• https://git.kernel.org/stable/c/6a36b05fc5b3d660fcc826133dc92e2fc87bd1de
• https://git.kernel.org/stable/c/f0c077c36fda9d498db39199e3997860e985efc8
• https://git.kernel.org/stable/c/d00d5f534a8238674755e59826a6c7d3c8efb870
• https://git.kernel.org/stable/c/c9716f956216eb74ab0aad7f633586edd49e0322
• https://git.kernel.org/stable/c/c8f4cfe1cf93bce924e27f2abead7a4c4a487505