[PATCH v6 28/31] KVM: nSVM: Sanitize TLB_CONTROL field when copying from vmcb12

[Yosry Ahmed]

The APM defines possible values for TLB_CONTROL as 0, 1, 3, and 7 -- all
of which are always allowed for KVM guests as KVM always supports
X86_FEATURE_FLUSHBYASID. Only copy bits 0 to 2 from vmcb12's
TLB_CONTROL, such that no unhandled or reserved bits end up in vmcb02.

Note that TLB_CONTROL in vmcb12 is currently ignored by KVM, as it nukes
the TLB on nested transitions anyway (see
nested_svm_transition_tlb_flush()). However, such sanitization will be
needed once the TODOs there are addressed, and it's minimal churn to add
it now.

Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
---
 arch/x86/include/asm/svm.h | 2 ++
 arch/x86/kvm/svm/nested.c  | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index c169256c415fb..16cf4f435aebd 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -182,6 +182,8 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 #define TLB_CONTROL_FLUSH_ASID 3
 #define TLB_CONTROL_FLUSH_ASID_LOCAL 7
 
+#define TLB_CONTROL_MASK GENMASK(2, 0)
+
 #define ERAP_CONTROL_ALLOW_LARGER_RAP BIT(0)
 #define ERAP_CONTROL_CLEAR_RAP BIT(1)
 
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 28a8bfc632ef5..d7c353ac42d88 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -502,7 +502,7 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->iopm_base_pa        = from->iopm_base_pa & PAGE_MASK;
 	to->msrpm_base_pa       = from->msrpm_base_pa & PAGE_MASK;
 	to->tsc_offset          = from->tsc_offset;
-	to->tlb_ctl             = from->tlb_ctl;
+	to->tlb_ctl             = from->tlb_ctl & TLB_CONTROL_MASK;
 	to->erap_ctl            = from->erap_ctl;
 	to->int_ctl             = from->int_ctl;
 	to->int_vector          = from->int_vector;
-- 
2.53.0.414.gf7e9f6c205-goog