[PATCH v4 28/28] KVM: TDX: Fix list_add corruption during vcpu_load()
From: Sean Christopherson <seanjc@google.com>
Date: 2025-10-30 20:11:08
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-coco, linux-mips, linux-riscv, lkml, loongarch
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
From: Yan Zhao <redacted>
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: d789fa6efac9 ("KVM: TDX: Handle vCPU dissociation")
Signed-off-by: Yan Zhao <redacted>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/tdx.c | 43 +++++++++++++++++++++++++++++++++++++-----
1 file changed, 38 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 762f2896547f..db7ac7955ca1 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c@@ -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;
--
2.51.1.930.gacf6e81ea2-goog