[PATCH v2 1/7] KVM: x86: Check EFER validity on KVM_SET_SREGS*

[PATCH v2 1/7] KVM: x86: Check EFER validity on KVM_SET_SREGS*

[Yosry Ahmed]

When handling userspace SREGS writes, check the validity of EFER (i.e.
allowed bits) before writing the new value of EFER through the
per-vendor set_efer callbacks. This prevents userspace from writing
bogus values (e.g. EFER.SVME=1 with nested=0).

Note: on KVM_SET_MSRS, KVM only checks EFER validity in terms of KVM
caps, not guest caps, so it is possible to set EFER bits that are
supported by KVM but not by the guest CPUID. Potentially allowing
userspace to set msrs before CPUID.

However, for KVM_SET_SREGS*, check the validity of the set bits against
both KVM and guest caps. This is consistent with other validity checks
(e.g. for CR4) that check validity against guest caps, which already
imposes the need to set CPUID before SREGS.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
 arch/x86/kvm/regs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index d2caf5a67dba4..94c4e4e41868f 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -563,7 +563,8 @@ static bool kvm_is_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 	}
 
 	return kvm_is_valid_cr4(vcpu, sregs->cr4) &&
-	       kvm_is_valid_cr0(vcpu, sregs->cr0);
+	       kvm_is_valid_cr0(vcpu, sregs->cr0) &&
+	       kvm_valid_efer(vcpu, sregs->efer);
 }
 
 static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,
-- 
2.55.0.rc2.803.g1fd1e6609c-goog

[PATCH v2 2/7] KVM: SVM: Disallow EFER.SVME and EFER.LSMLE if nested is disabled

[Yosry Ahmed]

Explicitly disallow setting EFER.SVME and EFER.LSMLE if nested
virtualization is disabled on SVM, to prevent the bits remaining allowed
if kvm_amd is loaded with nested=1 and then reloaded with nested=0.

This is a minimal fix for the benefit of stable backports, which will be
followed by a more systematic fix (moving efer_reserved_bits to
kvm_caps).

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
 arch/x86/kvm/msrs.c    | 8 +++++++-
 arch/x86/kvm/msrs.h    | 1 +
 arch/x86/kvm/svm/svm.c | 3 +++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c
index c230b18d87e38..45170df0ce40b 100644
--- a/arch/x86/kvm/msrs.c
+++ b/arch/x86/kvm/msrs.c
@@ -660,10 +660,16 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 void kvm_enable_efer_bits(u64 mask)
 {
-       efer_reserved_bits &= ~mask;
+	efer_reserved_bits &= ~mask;
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_enable_efer_bits);
 
+void kvm_disable_efer_bits(u64 mask)
+{
+	efer_reserved_bits |= mask;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_disable_efer_bits);
+
 bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type)
 {
 	struct kvm_x86_msr_filter *msr_filter;
diff --git a/arch/x86/kvm/msrs.h b/arch/x86/kvm/msrs.h
index b698983e37fb6..89f10447cdddf 100644
--- a/arch/x86/kvm/msrs.h
+++ b/arch/x86/kvm/msrs.h
@@ -59,6 +59,7 @@ int kvm_get_reg_list(struct kvm_vcpu *vcpu,
 		     struct kvm_reg_list __user *user_list);
 
 void kvm_enable_efer_bits(u64);
+void kvm_disable_efer_bits(u64);
 bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
 int kvm_emulate_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);
 int kvm_emulate_msr_write(struct kvm_vcpu *vcpu, u32 index, u64 data);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ef69a51ab27f9..1d51500238462 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5645,6 +5645,9 @@ static __init int svm_hardware_setup(void)
 		r = nested_svm_init_msrpm_merge_offsets();
 		if (r)
 			return r;
+	} else {
+		kvm_disable_efer_bits(EFER_SVME);
+		kvm_disable_efer_bits(EFER_LMSLE);
 	}
 
 	/*
-- 
2.55.0.rc2.803.g1fd1e6609c-goog