Gentle ping.
On 29/06/18 22:59, Liran Alon wrote:
When eVMCS is enabled, all VMCS allocated to be used by KVM are marked
with revision_id of KVM_EVMCS_VERSION instead of revision_id reported
by MSR_IA32_VMX_BASIC.
However, even though not explictly documented by TLFS, VMXArea passed
as VMXON argument should still be marked with revision_id reported by
physical CPU.
This issue was found by the following setup:
* L0 = KVM which expose eVMCS to it's L1 guest.
* L1 = KVM which consume eVMCS reported by L0.
This setup caused the following to occur:
1) L1 execute hardware_enable().
2) hardware_enable() calls kvm_cpu_vmxon() to execute VMXON.
3) L0 intercept L1 VMXON and execute handle_vmon() which notes
vmxarea->revision_id != VMCS12_REVISION and therefore fails with
nested_vmx_failInvalid() which sets RFLAGS.CF.
4) L1 kvm_cpu_vmxon() don't check RFLAGS.CF for failure and therefore
hardware_enable() continues as usual.
5) L1 hardware_enable() then calls ept_sync_global() which executes
INVEPT.
6) L0 intercept INVEPT and execute handle_invept() which notes
!vmx->nested.vmxon and thus raise a #UD to L1.
7) Raised #UD caused L1 to panic.
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1689f433f3a0..13d765e574ca 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4322,11 +4322,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
vmcs_conf->order = get_order(vmcs_conf->size);
vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
- /* KVM supports Enlightened VMCS v1 only */
- if (static_branch_unlikely(&enable_evmcs))
- vmcs_conf->revision_id = KVM_EVMCS_VERSION;
- else
- vmcs_conf->revision_id = vmx_msr_low;
+ vmcs_conf->revision_id = vmx_msr_low;
vmcs_conf->pin_based_exec_ctrl = _pin_based_exec_control;
vmcs_conf->cpu_based_exec_ctrl = _cpu_based_exec_control;
@@ -4396,7 +4392,13 @@ static struct vmcs *alloc_vmcs_cpu(int cpu)
return NULL;
vmcs = page_address(pages);
memset(vmcs, 0, vmcs_config.size);
- vmcs->revision_id = vmcs_config.revision_id; /* vmcs revision id */
+
+ /* KVM supports Enlightened VMCS v1 only */
+ if (static_branch_unlikely(&enable_evmcs))
+ vmcs->revision_id = KVM_EVMCS_VERSION;
+ else
+ vmcs->revision_id = vmcs_config.revision_id;
+
return vmcs;
}
@@ -4564,6 +4566,19 @@ static __init int alloc_kvm_area(void)
return -ENOMEM;
}
+ /*
+ * When eVMCS is enabled, alloc_vmcs_cpu() sets
+ * vmcs->revision_id to KVM_EVMCS_VERSION instead of
+ * revision_id reported by MSR_IA32_VMX_BASIC.
+ *
+ * However, even though not explictly documented by
+ * TLFS, VMXArea passed as VMXON argument should
+ * still be marked with revision_id reported by
+ * physical CPU.
+ */
+ if (static_branch_unlikely(&enable_evmcs))
+ vmcs->revision_id = vmcs_config.revision_id;
+
per_cpu(vmxarea, cpu) = vmcs;
}
return 0;
