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KVM: VMX: Mark VMXArea with revision_id of physical CPU even when eVMCS enabled 

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@oracle.com>
Cc: stable@vger.kernel.org
Fixes: 773e8a0425
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Liran Alon 2018-06-29 22:59:04 +03:00 committed by Paolo Bonzini
parent 9432a31757
commit 2307af1c4b
1 changed files with 21 additions and 6 deletions
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27
arch/x86/kvm/vmx.c
View File

@ -4108,11 +4108,7 @@ 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;
@ -4182,7 +4178,13 @@ 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;
}
@ -4341,6 +4343,19 @@ 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;