[PATCH v2 1/6] KVM: x86: Clear all supported MPX xfeatures if they are not all set

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Be a good citizen and don't allow any of the supported MPX xfeatures[1]
to be set if they can't all be set.  That way userspace or a guest
doesn't fail if it attempts to set them in XCR0.

[1] CPUID.(EAX=0DH,ECX=0):EAX.BNDREGS[bit-3]
    CPUID.(EAX=0DH,ECX=0):EAX.BNDCSR[bit-4]

Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Aaron Lewis <aaronlewis@xxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c4e8257629165..2431c46d456b4 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -855,6 +855,16 @@ static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func)
 	return 0;
 }
 
+static u64 sanitize_xcr0(u64 xcr0)
+{
+	u64 mask;
+
+	mask = XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR;
+	if ((xcr0 & mask) != mask)
+		xcr0 &= ~mask;
+
+	return xcr0;
+}
+
 static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 {
 	struct kvm_cpuid_entry2 *entry;
@@ -982,6 +992,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		u64 permitted_xcr0 = kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
 		u64 permitted_xss = kvm_caps.supported_xss;
 
+		permitted_xcr0 = sanitize_xcr0(permitted_xcr0);
+
 		entry->eax &= permitted_xcr0;
 		entry->ebx = xstate_required_size(permitted_xcr0, false);
 		entry->ecx = entry->ebx;
-- 
2.39.0.314.g84b9a713c41-goog




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