[PATCH 0/2] KVM: nSVM: Check MBZ bits in CR3 and CR4 on vmrun of nested guests

[PATCH 0/2] KVM: nSVM: Check MBZ bits in CR3 and CR4 on vmrun of nested guests

[Krish Sadhukhan]

Patch# 1: Adds the required KVM check.
Patch# 2: Adds the kvm-unit-test.

[PATCH 1/2] KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun
[PATCH 2/2] kvm-unit-tests: nSVM: Test that MBZ bits in CR3 and CR4 are not set on vmrun

 arch/x86/kvm/svm/nested.c | 18 ++++++++++++++++++
 arch/x86/kvm/svm/svm.h    |  7 ++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

Krish Sadhukhan (1):
      nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested gu
 x86/svm.h       |   6 ++++
 x86/svm_tests.c | 105 +++++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 99 insertions(+), 12 deletions(-)

Krish Sadhukhan (1):
      nSVM: Test that MBZ bits in CR3 and CR4 are not set on vmrun of nested gue

[PATCH 1/2] KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests

[Krish Sadhukhan]

According to section "Canonicalization and Consistency Checks" in APM vol. 2
the following guest state is illegal:

    "Any MBZ bit of CR3 is set."
    "Any MBZ bit of CR4 is set."

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>

---
 arch/x86/kvm/svm/nested.c | 18 ++++++++++++++++++
 arch/x86/kvm/svm/svm.h    |  7 ++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 90a1ca9..1804a97 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -207,6 +207,24 @@ static bool nested_vmcb_checks(struct vmcb *vmcb)
 	if ((vmcb->save.efer & EFER_SVME) == 0)
 		return false;
 
+	if (!(vmcb->save.efer & EFER_LMA)) {
+		if (vmcb->save.cr4 & X86_CR4_PAE) {
+			if (vmcb->save.cr3 & MSR_CR3_LEGACY_PAE_RESERVED_MASK)
+				return false;
+		} else {
+			if (vmcb->save.cr3 & MSR_CR3_LEGACY_RESERVED_MASK)
+				return false;
+		}
+		if (vmcb->save.cr4 & MSR_CR4_LEGACY_RESERVED_MASK)
+			return false;
+	} else {
+		if ((vmcb->save.cr4 & X86_CR4_PAE) &&
+		    (vmcb->save.cr3 & MSR_CR3_LONG_RESERVED_MASK))
+			return false;
+		if (vmcb->save.cr4 & MSR_CR4_RESERVED_MASK)
+			return false;
+	}
+
 	if ((vmcb->control.intercept & (1ULL << INTERCEPT_VMRUN)) == 0)
 		return false;
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index df3474f..796c083 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -354,7 +354,12 @@ static inline bool gif_set(struct vcpu_svm *svm)
 }
 
 /* svm.c */
-#define MSR_INVALID			0xffffffffU
+#define MSR_CR3_LEGACY_RESERVED_MASK		0xfe7U
+#define MSR_CR3_LEGACY_PAE_RESERVED_MASK	0x7U
+#define MSR_CR3_LONG_RESERVED_MASK		0xfff0000000000fe7U
+#define MSR_CR4_LEGACY_RESERVED_MASK		0xffbaf000U
+#define MSR_CR4_RESERVED_MASK			0xffffffffffbaf000U
+#define MSR_INVALID				0xffffffffU
 
 u32 svm_msrpm_offset(u32 msr);
 void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
-- 
1.8.3.1

[PATCH 2/2] kvm-unit-tests: nSVM: Test that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests

[Krish Sadhukhan]

According to section "Canonicalization and Consistency Checks" in APM vol. 2,
the following guest state is illegal:

	"Any MBZ bit of CR3 is set."
	"Any MBZ bit of CR4 is set."

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>

---
 x86/svm.h       |   6 ++++
 x86/svm_tests.c | 105 +++++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 99 insertions(+), 12 deletions(-)

diff --git a/x86/svm.h b/x86/svm.h
index 645deb7..3d5b79c 100644
--- a/x86/svm.h
+++ b/x86/svm.h
@@ -323,6 +323,12 @@ struct __attribute__ ((__packed__)) vmcb {
 #define SVM_EXIT_ERR		-1
 
 #define SVM_CR0_SELECTIVE_MASK (X86_CR0_TS | X86_CR0_MP)
+#define	SVM_CR0_RESERVED_MASK			0xffffffff00000000U
+#define	SVM_CR3_LEGACY_RESERVED_MASK		0xfe7U
+#define	SVM_CR3_LEGACY_PAE_RESERVED_MASK	0x7U
+#define	SVM_CR3_LONG_RESERVED_MASK		0xfff0000000000fe7U
+#define	SVM_CR4_LEGACY_RESERVED_MASK		0xffbaf000U
+#define	SVM_CR4_RESERVED_MASK			0xffffffffffbaf000U
 
 #define MSR_BITMAP_SIZE 8192
 
diff --git a/x86/svm_tests.c b/x86/svm_tests.c
index 5a571eb..5d57ad0 100644
--- a/x86/svm_tests.c
+++ b/x86/svm_tests.c
@@ -1596,6 +1596,31 @@ static void basic_guest_main(struct svm_test *test)
 {
 }
 
+#define SVM_TEST_CR_RESERVED_BITS(start, end, inc, cr, val, resv_mask)	\
+{									\
+        u64 tmp, mask;							\
+        int i;								\
+									\
+        for (i = start; i <= end; i = i + inc) {			\
+                mask = 1ull << i;					\
+                if (!(mask & resv_mask))				\
+                        continue;					\
+                tmp = val | mask;					\
+                switch (cr) {						\
+                        case 0:						\
+                                vmcb->save.cr0 = tmp;			\
+                                break;					\
+                        case 3:						\
+                                vmcb->save.cr3 = tmp;			\
+                                break;					\
+                        case 4:						\
+                                vmcb->save.cr4 = tmp;			\
+                }							\
+                report(svm_vmrun() == SVM_EXIT_ERR, "Test CR%d %d:%d: %lx",\
+		    cr, end, start, tmp);				\
+        }								\
+}
+
 static void svm_guest_state_test(void)
 {
 	test_set_guest(basic_guest_main);
@@ -1621,32 +1646,88 @@ static void svm_guest_state_test(void)
 	cr0 |= X86_CR0_CD;
 	cr0 &= ~X86_CR0_NW;
 	vmcb->save.cr0 = cr0;
-	report (svm_vmrun() == SVM_EXIT_VMMCALL, "CR0: %lx", cr0);
+	report (svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR0 CD=1,NW=0: %lx",
+	    cr0);
 	cr0 |= X86_CR0_NW;
 	vmcb->save.cr0 = cr0;
-	report (svm_vmrun() == SVM_EXIT_VMMCALL, "CR0: %lx", cr0);
+	report (svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR0 CD=1,NW=1: %lx",
+	    cr0);
 	cr0 &= ~X86_CR0_NW;
 	cr0 &= ~X86_CR0_CD;
 	vmcb->save.cr0 = cr0;
-	report (svm_vmrun() == SVM_EXIT_VMMCALL, "CR0: %lx", cr0);
+	report (svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR0 CD=0,NW=0: %lx",
+	    cr0);
 	cr0 |= X86_CR0_NW;
 	vmcb->save.cr0 = cr0;
-	report (svm_vmrun() == SVM_EXIT_ERR, "CR0: %lx", cr0);
+	report (svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR0 CD=0,NW=1: %lx",
+	    cr0);
 	vmcb->save.cr0 = cr0_saved;
 
 	/*
 	 * CR0[63:32] are not zero
 	 */
-	int i;
-
 	cr0 = cr0_saved;
-	for (i = 32; i < 63; i = i + 4) {
-		cr0 = cr0_saved | (1ull << i);
-		vmcb->save.cr0 = cr0;
-		report (svm_vmrun() == SVM_EXIT_ERR, "CR0[63:32]: %lx",
-		    cr0 >> 32);
-	}
+
+	SVM_TEST_CR_RESERVED_BITS(32, 63, 4, 0, cr0_saved,
+	    SVM_CR0_RESERVED_MASK);
 	vmcb->save.cr0 = cr0_saved;
+
+	/*
+	 * CR3 MBZ bits based on different modes:
+	 *   [2:0]		    - legacy PAE
+	 *   [2:0], [11:5]	    - legacy non-PAE
+	 *   [2:0], [11:5], [63:52] - long mode
+	 */
+	u64 cr3_saved = vmcb->save.cr3;
+	u64 cr4_saved = vmcb->save.cr4;
+	u64 cr4 = cr4_saved;
+	efer_saved = vmcb->save.efer;
+	efer = efer_saved;
+
+	efer &= ~EFER_LMA;
+	vmcb->save.efer = efer;
+	cr4 |= X86_CR4_PAE;
+	vmcb->save.cr4 = cr4;
+	SVM_TEST_CR_RESERVED_BITS(0, 2, 1, 3, cr3_saved,
+	    SVM_CR3_LEGACY_PAE_RESERVED_MASK);
+
+	cr4 = cr4_saved & ~X86_CR4_PAE;
+	vmcb->save.cr4 = cr4;
+	SVM_TEST_CR_RESERVED_BITS(0, 11, 2, 3, cr3_saved,
+	    SVM_CR3_LEGACY_RESERVED_MASK);
+
+	cr4 |= X86_CR4_PAE;
+	vmcb->save.cr4 = cr4;
+	efer |= EFER_LMA;
+	vmcb->save.efer = efer;
+	SVM_TEST_CR_RESERVED_BITS(0, 63, 2, 3, cr3_saved,
+	    SVM_CR3_LONG_RESERVED_MASK);
+
+	vmcb->save.cr4 = cr4_saved;
+	vmcb->save.cr3 = cr3_saved;
+	vmcb->save.efer = efer_saved;
+
+	/*
+	 * CR4 MBZ bits based on different modes:
+	 *   [15:12], 17, 19, [31:22] - legacy mode
+	 *   [15:12], 17, 19, [63:22] - long mode
+	 */
+	cr4_saved = vmcb->save.cr4;
+	efer_saved = vmcb->save.efer;
+	efer &= ~EFER_LMA;
+	vmcb->save.efer = efer;
+	SVM_TEST_CR_RESERVED_BITS(12, 31, 2, 4, cr4_saved,
+	    SVM_CR4_LEGACY_RESERVED_MASK);
+
+	efer |= EFER_LMA;
+	vmcb->save.efer = efer;
+	SVM_TEST_CR_RESERVED_BITS(12, 31, 2, 4, cr4_saved,
+	    SVM_CR4_RESERVED_MASK);
+	SVM_TEST_CR_RESERVED_BITS(32, 63, 4, 4, cr4_saved,
+	    SVM_CR4_RESERVED_MASK);
+
+	vmcb->save.cr4 = cr4_saved;
+	vmcb->save.efer = efer_saved;
 }
 
 struct svm_test svm_tests[] = {
-- 
1.8.3.1

Re: [PATCH 1/2] KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests

[Paolo Bonzini]

On 05/05/20 00:35, Krish Sadhukhan wrote:
> +	if (!(vmcb->save.efer & EFER_LMA)) {
> +		if (vmcb->save.cr4 & X86_CR4_PAE) {
> +			if (vmcb->save.cr3 & MSR_CR3_LEGACY_PAE_RESERVED_MASK)
> +				return false;
> +		} else {
> +			if (vmcb->save.cr3 & MSR_CR3_LEGACY_RESERVED_MASK)
> +				return false;
> +		}
> +		if (vmcb->save.cr4 & MSR_CR4_LEGACY_RESERVED_MASK)
> +			return false;
> +	} else {
> +		if ((vmcb->save.cr4 & X86_CR4_PAE) &&
> +		    (vmcb->save.cr3 & MSR_CR3_LONG_RESERVED_MASK))
> +			return false;
> +		if (vmcb->save.cr4 & MSR_CR4_RESERVED_MASK)
> +			return false;
> +	}
> +
>  	if ((vmcb->control.intercept & (1ULL << INTERCEPT_VMRUN)) == 0)
>  		return false;
>  

I think checking LMA from the guest state is incorrect, the number of
bits in CR3 and CR4 remains 64 as long as the host processor is 64-bits.
 This of course is unless you have reproduced on bare metal that a
hypervisor running in 32-bit mode ignores the top 32 bits.

Also, the checks for CR4 must use the guest's reserved bits, using
kvm_valid_cr4.  However this can be a bit slow so it is probably a good
idea to cache the bits in kvm_update_cpuid.

Thanks,

Paolo

> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index df3474f..796c083 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -354,7 +354,12 @@ static inline bool gif_set(struct vcpu_svm *svm)
>  }
>  
>  /* svm.c */
> -#define MSR_INVALID			0xffffffffU
> +#define MSR_CR3_LEGACY_RESERVED_MASK		0xfe7U
> +#define MSR_CR3_LEGACY_PAE_RESERVED_MASK	0x7U
> +#define MSR_CR3_LONG_RESERVED_MASK		0xfff0000000000fe7U
> +#define MSR_CR4_LEGACY_RESERVED_MASK		0xffbaf000U
> +#define MSR_CR4_RESERVED_MASK			0xffffffffffbaf000U
> +#define MSR_INVALID				0xffffffffU
>