Commit 1e3a825c authored by Yan Zhao's avatar Yan Zhao Committed by Sean Christopherson
Browse files

KVM: TDX: Fix list_add corruption during vcpu_load() 



During vCPU creation, a vCPU may be destroyed immediately after
kvm_arch_vcpu_create() (e.g., due to vCPU id confiliction). However, the
vcpu_load() inside kvm_arch_vcpu_create() may have associate the vCPU to
pCPU via "list_add(&tdx->cpu_list, &per_cpu(associated_tdvcpus, cpu))"
before invoking tdx_vcpu_free().

Though there's no need to invoke tdh_vp_flush() on the vCPU, failing to
dissociate the vCPU from pCPU (i.e., "list_del(&to_tdx(vcpu)->cpu_list)")
will cause list corruption of the per-pCPU list associated_tdvcpus.

Then, a later list_add() during vcpu_load() would detect list corruption
and print calltrace as shown below.

Dissociate a vCPU from its associated pCPU in tdx_vcpu_free() for the vCPUs
destroyed immediately after creation which must be in
VCPU_TD_STATE_UNINITIALIZED state.

kernel BUG at lib/list_debug.c:29!
Oops: invalid opcode: 0000 [#2] SMP NOPTI
RIP: 0010:__list_add_valid_or_report+0x82/0xd0

Call Trace:
 <TASK>
 tdx_vcpu_load+0xa8/0x120
 vt_vcpu_load+0x25/0x30
 kvm_arch_vcpu_load+0x81/0x300
 vcpu_load+0x55/0x90
 kvm_arch_vcpu_create+0x24f/0x330
 kvm_vm_ioctl_create_vcpu+0x1b1/0x53
 kvm_vm_ioctl+0xc2/0xa60
  __x64_sys_ioctl+0x9a/0xf0
 x64_sys_call+0x10ee/0x20d0
 do_syscall_64+0xc3/0x470
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: d789fa6e ("KVM: TDX: Handle vCPU dissociation")
Signed-off-by: default avatarYan Zhao <yan.y.zhao@intel.com>
Reviewed-by: default avatarKai Huang <kai.huang@intel.com>
Reviewed-by: default avatarYan Zhao <yan.y.zhao@intel.com>
Tested-by: default avatarYan Zhao <yan.y.zhao@intel.com>
Tested-by: default avatarKai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-29-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent ad44aa4c

arch/x86/kvm/vmx/tdx.c

+38 −5
Original line number Diff line number Diff line
@@ -843,19 +843,52 @@ void tdx_vcpu_put(struct kvm_vcpu *vcpu) 
	tdx_prepare_switch_to_host(vcpu);

}



/*

 * Life cycles for a TD and a vCPU:

 * 1. KVM_CREATE_VM ioctl.

 *    TD state is TD_STATE_UNINITIALIZED.

 *    hkid is not assigned at this stage.

 * 2. KVM_TDX_INIT_VM ioctl.

 *    TD transitions to TD_STATE_INITIALIZED.

 *    hkid is assigned after this stage.

 * 3. KVM_CREATE_VCPU ioctl. (only when TD is TD_STATE_INITIALIZED).

 *    3.1 tdx_vcpu_create() transitions vCPU state to VCPU_TD_STATE_UNINITIALIZED.

 *    3.2 vcpu_load() and vcpu_put() in kvm_arch_vcpu_create().

 *    3.3 (conditional) if any error encountered after kvm_arch_vcpu_create()

 *        kvm_arch_vcpu_destroy() --> tdx_vcpu_free().

 * 4. KVM_TDX_INIT_VCPU ioctl.

 *    tdx_vcpu_init() transitions vCPU state to VCPU_TD_STATE_INITIALIZED.

 *    vCPU control structures are allocated at this stage.

 * 5. kvm_destroy_vm().

 *    5.1 tdx_mmu_release_hkid(): (1) tdh_vp_flush(), disassociates all vCPUs.

 *                                (2) puts hkid to !assigned state.

 *    5.2 kvm_destroy_vcpus() --> tdx_vcpu_free():

 *        transitions vCPU to VCPU_TD_STATE_UNINITIALIZED state.

 *    5.3 tdx_vm_destroy()

 *        transitions TD to TD_STATE_UNINITIALIZED state.

 *

 * tdx_vcpu_free() can be invoked only at 3.3 or 5.2.

 * - If at 3.3, hkid is still assigned, but the vCPU must be in

 *   VCPU_TD_STATE_UNINITIALIZED state.

 * - if at 5.2, hkid must be !assigned and all vCPUs must be in

 *   VCPU_TD_STATE_INITIALIZED state and have been dissociated.

 */

void tdx_vcpu_free(struct kvm_vcpu *vcpu)

{

	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);

	struct vcpu_tdx *tdx = to_tdx(vcpu);

	int i;



	if (vcpu->cpu != -1) {

		KVM_BUG_ON(tdx->state == VCPU_TD_STATE_INITIALIZED, vcpu->kvm);

		tdx_flush_vp_on_cpu(vcpu);

		return;

	}



	/*

	 * It is not possible to reclaim pages while hkid is assigned. It might

	 * be assigned if:

	 * 1. the TD VM is being destroyed but freeing hkid failed, in which

	 * case the pages are leaked

	 * 2. TD VCPU creation failed and this on the error path, in which case

	 * there is nothing to do anyway

	 * be assigned if the TD VM is being destroyed but freeing hkid failed,

	 * in which case the pages are leaked.

	 */

	if (is_hkid_assigned(kvm_tdx))

		return;