[PATCH 0/3] KVM: nVMX: tighten some KVM_SET_NESTED_STATE validity checks

[PATCH 0/3] KVM: nVMX: tighten some KVM_SET_NESTED_STATE validity checks

[Paolo Bonzini]

Patch 1 is a fix to the tests so that we can cover the new cases properly.
Patches 2-3 check for more cases of invalid nested state data.

Paolo

Paolo Bonzini (3):
  selftests: kvm: do not set guest mode flag
  KVM: nVMX: check for required but missing VMCS12 in
    KVM_SET_NESTED_STATE
  KVM: nVMX: check for invalid hdr.vmx.flags

 arch/x86/kvm/vmx/nested.c                     | 16 +++++--
 arch/x86/kvm/vmx/nested.h                     |  5 +++
 .../kvm/x86_64/vmx_set_nested_state_test.c    | 42 +++++++++++++++----
 3 files changed, 51 insertions(+), 12 deletions(-)

-- 
2.26.2

[PATCH 1/3] selftests: kvm: do not set guest mode flag

[Paolo Bonzini]

Setting KVM_STATE_NESTED_GUEST_MODE enables various consistency checks
on VMCS12 and therefore causes KVM_SET_NESTED_STATE to fail spuriously
with -EINVAL.  Do not set the flag so that we're sure to cover the
conditions included by the test, and cover the case where VMCS12 is
set and KVM_SET_NESTED_STATE is called with invalid VMCS12 contents.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 .../kvm/x86_64/vmx_set_nested_state_test.c      | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
index 54cdefdfb49d..d14a34f1b018 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
@@ -76,10 +76,8 @@ void set_default_state(struct kvm_nested_state *state)
 void set_default_vmx_state(struct kvm_nested_state *state, int size)
 {
 	memset(state, 0, size);
-	state->flags = KVM_STATE_NESTED_GUEST_MODE  |
-			KVM_STATE_NESTED_RUN_PENDING;
 	if (have_evmcs)
-		state->flags |= KVM_STATE_NESTED_EVMCS;
+		state->flags = KVM_STATE_NESTED_EVMCS;
 	state->format = 0;
 	state->size = size;
 	state->hdr.vmx.vmxon_pa = 0x1000;
@@ -190,17 +188,20 @@ void test_vmx_nested_state(struct kvm_vm *vm)
 	state->size = sizeof(*state);
 	test_nested_state(vm, state);
 
+	/*
+	 * KVM_SET_NESTED_STATE succeeds with invalid VMCS
+	 * contents but L2 not running.
+	 */
+	set_default_vmx_state(state, state_sz);
+	state->flags = 0;
+	test_nested_state(vm, state);
+
 	/* vmxon_pa cannot be the same address as vmcs_pa. */
 	set_default_vmx_state(state, state_sz);
 	state->hdr.vmx.vmxon_pa = 0;
 	state->hdr.vmx.vmcs12_pa = 0;
 	test_nested_state_expect_einval(vm, state);
 
-	/* The revision id for vmcs12 must be VMCS12_REVISION. */
-	set_default_vmx_state(state, state_sz);
-	set_revision_id_for_vmcs12(state, 0);
-	test_nested_state_expect_einval(vm, state);
-
 	/*
 	 * Test that if we leave nesting the state reflects that when we get
 	 * it again.
-- 
2.26.2

[PATCH 2/3] KVM: nVMX: check for required but missing VMCS12 in KVM_SET_NESTED_STATE

[Paolo Bonzini]

A missing VMCS12 was not causing -EINVAL (it was just read with
copy_from_user, so it is not a security issue, but it is still
wrong).  Test for VMCS12 validity and reject the nested state
if a VMCS12 is required but not present.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c                           | 13 ++++++++++---
 arch/x86/kvm/vmx/nested.h                           |  5 +++++
 .../kvm/x86_64/vmx_set_nested_state_test.c          | 12 +++++++++++-
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index d4a4cec034d0..6a0e32a7418c 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6108,9 +6108,16 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	if (ret)
 		return ret;
 
-	/* Empty 'VMXON' state is permitted */
-	if (kvm_state->size < sizeof(*kvm_state) + sizeof(*vmcs12))
-		return 0;
+	/* Empty VMX data is permitted if no VMCS loaded */
+	if (kvm_state->size < sizeof(*kvm_state) + sizeof(*vmcs12)) {
+		/* See vmx_has_valid_vmcs12.  */
+		if ((kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE) ||
+		    (kvm_state->flags & KVM_STATE_NESTED_EVMCS) ||
+		    (kvm_state->hdr.vmx.vmcs12_pa != -1ull))
+			return -EINVAL;
+		else
+			return 0;
+	}
 
 	if (kvm_state->hdr.vmx.vmcs12_pa != -1ull) {
 		if (kvm_state->hdr.vmx.vmcs12_pa == kvm_state->hdr.vmx.vmxon_pa ||
diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index 758bccc26cf9..197148d76b8f 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -47,6 +47,11 @@ static inline struct vmcs12 *get_shadow_vmcs12(struct kvm_vcpu *vcpu)
 	return to_vmx(vcpu)->nested.cached_shadow_vmcs12;
 }
 
+/*
+ * Note: the same condition is checked against the state provided by userspace
+ * in vmx_set_nested_state; if it is satisfied, the nested state must include
+ * the VMCS12.
+ */
 static inline int vmx_has_valid_vmcs12(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
diff --git a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
index d14a34f1b018..94f28a657569 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
@@ -183,9 +183,19 @@ void test_vmx_nested_state(struct kvm_vm *vm)
 	state->hdr.vmx.smm.flags = KVM_STATE_NESTED_SMM_GUEST_MODE;
 	test_nested_state_expect_einval(vm, state);
 
-	/* Size must be large enough to fit kvm_nested_state and vmcs12. */
+	/*
+	 * Size must be large enough to fit kvm_nested_state and vmcs12
+	 * if VMCS12 physical address is set
+	 */
+	set_default_vmx_state(state, state_sz);
+	state->size = sizeof(*state);
+	state->flags = 0;
+	test_nested_state_expect_einval(vm, state);
+
 	set_default_vmx_state(state, state_sz);
 	state->size = sizeof(*state);
+	state->flags = 0;
+	state->hdr.vmx.vmcs12_pa = -1;
 	test_nested_state(vm, state);
 
 	/*
-- 
2.26.2

[PATCH 3/3] KVM: nVMX: check for invalid hdr.vmx.flags

[Paolo Bonzini]

hdr.vmx.flags is meant for future extensions to the ABI, rejecting
invalid flags is necessary to avoid broken half-loads of the
nVMX state.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c                           |  3 +++
 .../kvm/x86_64/vmx_set_nested_state_test.c          | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 6a0e32a7418c..11e4df560018 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6079,6 +6079,9 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	    ~(KVM_STATE_NESTED_SMM_GUEST_MODE | KVM_STATE_NESTED_SMM_VMXON))
 		return -EINVAL;
 
+	if (kvm_state->hdr.vmx.flags & ~KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE)
+		return -EINVAL;
+
 	/*
 	 * SMM temporarily disables VMX, so we cannot be in guest mode,
 	 * nor can VMLAUNCH/VMRESUME be pending.  Outside SMM, SMM flags
diff --git a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
index 94f28a657569..d59f3eb67c8f 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
@@ -146,6 +146,11 @@ void test_vmx_nested_state(struct kvm_vm *vm)
 	state->hdr.vmx.smm.flags = 1;
 	test_nested_state_expect_einval(vm, state);
 
+	/* Invalid flags are rejected. */
+	set_default_vmx_state(state, state_sz);
+	state->hdr.vmx.flags = ~0;
+	test_nested_state_expect_einval(vm, state);
+
 	/* It is invalid to have vmxon_pa == -1ull and vmcs_pa != -1ull. */
 	set_default_vmx_state(state, state_sz);
 	state->hdr.vmx.vmxon_pa = -1ull;
@@ -206,6 +211,14 @@ void test_vmx_nested_state(struct kvm_vm *vm)
 	state->flags = 0;
 	test_nested_state(vm, state);
 
+	/* Invalid flags are rejected, even if no VMCS loaded. */
+	set_default_vmx_state(state, state_sz);
+	state->size = sizeof(*state);
+	state->flags = 0;
+	state->hdr.vmx.vmcs12_pa = -1;
+	state->hdr.vmx.flags = ~0;
+	test_nested_state_expect_einval(vm, state);
+
 	/* vmxon_pa cannot be the same address as vmcs_pa. */
 	set_default_vmx_state(state, state_sz);
 	state->hdr.vmx.vmxon_pa = 0;
-- 
2.26.2