[PATCH] Fix possible FPU information on SVM

["Joerg Roedel" <joerg.roedel-5C7GfCeVMHo@public.gmane.org>]

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From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

On AMD K8 processors the fxsave/fxrstor instructions do not save and
restore the x87 error pointers FIP/FOP and FDP except the ES bit in the
status word is set. This could lead to information leakage from host to
guest and vice versa. This patch fixes this by setting the error
pointers to defined values on FPU state switch in KVM.

Signed-off-by: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

-- 
           |           AMD Saxony Limited Liability Company & Co. KG
 Operating |         Wilschdorfer Landstr. 101, 01109 Dresden, Germany
 System    |                  Register Court Dresden: HRA 4896
 Research  |              General Partner authorized to represent:
 Center    |             AMD Saxony LLC (Wilmington, Delaware, US)
           | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy

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diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index ed33f59..f2d5ab0 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1474,6 +1474,18 @@ static void load_db_regs(unsigned long *db_regs)
 	asm volatile ("mov %0, %%dr3" : : "r"(db_regs[3]));
 }
 
+/* pass data that is likly in L1 here */
+static inline void fx_clear_error_pointers(void *data)
+{
+	/*
+	 * AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception is
+	 * pending. So this function is used to set these registers to defined
+	 * values.
+	 */
+	asm volatile ("emms\n"
+		      "fildl %[addr]\n" :: [addr] "m" (data));
+}
+
 static int svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
 	u16 fs_selector;
@@ -1510,6 +1522,7 @@ again:
 
 	if (vcpu->fpu_active) {
 		fx_save(vcpu->host_fx_image);
+		fx_clear_error_pointers(vcpu->svm->vmcb);
 		fx_restore(vcpu->guest_fx_image);
 	}
 
@@ -1624,6 +1637,7 @@ again:
 
 	if (vcpu->fpu_active) {
 		fx_save(vcpu->guest_fx_image);
+		fx_clear_error_pointers(vcpu->svm->vmcb);
 		fx_restore(vcpu->host_fx_image);
 	}
 

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