CVE-2023-53756

In the Linux kernel, the following vulnerability has been resolved:

KVM: VMX: Fix crash due to uninitialized current_vmcs

KVM enables Enlightened VMCS and Enlightened MSR Bitmap when running as a nested hypervisor on top of Hyper-V. When MSR bitmap is updated, evmcs_touch_msr_bitmap function uses current_vmcs per-cpu variable to mark that the msr bitmap was changed.

vmx_vcpu_create() modifies the msr bitmap via vmx_disable_intercept_for_msr -> vmx_msr_bitmap_l01_changed which in the end calls this function. The function checks for current_vmcs if it is null but the check is insufficient because current_vmcs is not initialized. Because of this, the code might incorrectly write to the structure pointed by current_vmcs value left by another task. Preemption is not disabled, the current task can be preempted and moved to another CPU while current_vmcs is accessed multiple times from evmcs_touch_msr_bitmap() which leads to crash.

The manipulation of MSR bitmaps by callers happens only for vmcs01 so the solution is to use vmx->vmcs01.vmcs instead of current_vmcs.

BUG: kernel NULL pointer dereference, address: 0000000000000338 PGD 4e1775067 P4D 0 Oops: 0002 [#1] PREEMPT SMP NOPTI … RIP: 0010:vmx_msr_bitmap_l01_changed+0x39/0x50 [kvm_intel] … Call Trace: vmx_disable_intercept_for_msr+0x36/0x260 [kvm_intel] vmx_vcpu_create+0xe6/0x540 [kvm_intel] kvm_arch_vcpu_create+0x1d1/0x2e0 [kvm] kvm_vm_ioctl_create_vcpu+0x178/0x430 [kvm] kvm_vm_ioctl+0x53f/0x790 [kvm] __x64_sys_ioctl+0x8a/0xc0 do_syscall_64+0x5c/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Affected Software

References

• https://git.kernel.org/stable/c/3ba95cc671c025d0d2a1c7d5e2930f0ff0980cf4
• https://git.kernel.org/stable/c/6baebcecf09acd19e2bab1c2911dcdba5d48a1dc
• https://git.kernel.org/stable/c/6e7bc50f97c9855da83f1478f722590defd45ff2
• https://git.kernel.org/stable/c/93827a0a36396f2fd6368a54a020f420c8916e9b
• https://git.kernel.org/stable/c/b2de2b4d4e007f9add46ea8dc06f781835e3ea9f