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KVM: vmx: Inject #UD for SGX ENCLS instruction in guest

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Virtualization of Intel SGX depends on Enclave Page Cache (EPC)
management that is not yet available in the kernel, i.e. KVM support
for exposing SGX to a guest cannot be added until basic support
for SGX is upstreamed, which is a WIP[1].

Until SGX is properly supported in KVM, ensure a guest sees expected
behavior for ENCLS, i.e. all ENCLS #UD.  Because SGX does not have a
true software enable bit, e.g. there is no CR4.SGXE bit, the ENCLS
instruction can be executed[1] by the guest if SGX is supported by the
system.  Intercept all ENCLS leafs (via the ENCLS- exiting control and
field) and unconditionally inject #UD.

[1] https://www.spinics.net/lists/kvm/msg171333.html or
    https://lkml.org/lkml/2018/7/3/879

[2] A guest can execute ENCLS in the sense that ENCLS will not take
    an immediate #UD, but no ENCLS will ever succeed in a guest
    without explicit support from KVM (map EPC memory into the guest),
    unless KVM has a *very* egregious bug, e.g. accidentally mapped
    EPC memory into the guest SPTEs.  In other words this patch is
    needed only to prevent the guest from seeing inconsistent behavior,
    e.g. #GP (SGX not enabled in Feature Control MSR) or #PF (leaf
    operand(s) does not point at EPC memory) instead of #UD on ENCLS.
    Intercepting ENCLS is not required to prevent the guest from truly
    utilizing SGX.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20180814163334.25724-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2018-08-14 09:33:34 -07:00 committed by Paolo Bonzini
parent 802ec46167
commit 0b665d3040
1 changed files with 29 additions and 1 deletions
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30
arch/x86/kvm/vmx.c
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@ -1684,6 +1684,12 @@ static inline bool cpu_has_vmx_virtual_intr_delivery(void)
SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY;
}
static inline bool cpu_has_vmx_encls_vmexit(void)
{
return vmcs_config.cpu_based_2nd_exec_ctrl &
SECONDARY_EXEC_ENCLS_EXITING;
}
/*
* Comment's format: document - errata name - stepping - processor name.
* Refer from
@ -4551,7 +4557,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
SECONDARY_EXEC_RDRAND_EXITING |
SECONDARY_EXEC_ENABLE_PML |
SECONDARY_EXEC_TSC_SCALING |
SECONDARY_EXEC_ENABLE_VMFUNC;
SECONDARY_EXEC_ENABLE_VMFUNC |
SECONDARY_EXEC_ENCLS_EXITING;
if (adjust_vmx_controls(min2, opt2,
MSR_IA32_VMX_PROCBASED_CTLS2,
&_cpu_based_2nd_exec_control) < 0)
@ -6648,6 +6655,9 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmcs_write64(PML_ADDRESS, page_to_phys(vmx->pml_pg));
vmcs_write16(GUEST_PML_INDEX, PML_ENTITY_NUM - 1);
}
if (cpu_has_vmx_encls_vmexit())
vmcs_write64(ENCLS_EXITING_BITMAP, -1ull);
}
static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
@ -9314,6 +9324,17 @@ fail:
return 1;
}
static int handle_encls(struct kvm_vcpu *vcpu)
{
/*
* SGX virtualization is not yet supported. There is no software
* enable bit for SGX, so we have to trap ENCLS and inject a #UD
* to prevent the guest from executing ENCLS.
*/
kvm_queue_exception(vcpu, UD_VECTOR);
return 1;
}
/*
* The exit handlers return 1 if the exit was handled fully and guest execution
* may resume. Otherwise they set the kvm_run parameter to indicate what needs
@ -9371,6 +9392,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_INVPCID] = handle_invpcid,
[EXIT_REASON_VMFUNC] = handle_vmfunc,
[EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
[EXIT_REASON_ENCLS] = handle_encls,
};
static const int kvm_vmx_max_exit_handlers =
@ -9741,6 +9763,9 @@ static bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
case EXIT_REASON_VMFUNC:
/* VM functions are emulated through L2->L0 vmexits. */
return false;
case EXIT_REASON_ENCLS:
/* SGX is never exposed to L1 */
return false;
default:
return true;
}
@ -12101,6 +12126,9 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
if (exec_control & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)
vmcs_write64(APIC_ACCESS_ADDR, -1ull);
if (exec_control & SECONDARY_EXEC_ENCLS_EXITING)
vmcs_write64(ENCLS_EXITING_BITMAP, -1ull);
vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
}