Commit 893a5ab6 authored Jan 14, 2011 by Joerg Roedel Committed by Avi Kivity Feb 09, 2011

KVM: SVM: Make sure KERNEL_GS_BASE is valid when loading gs_index



The gs_index loading code uses the swapgs instruction to
switch to the user gs_base temporarily. This is unsave in an
lightweight exit-path in KVM on AMD because the
KERNEL_GS_BASE MSR is switches lazily. An NMI happening in
the critical path of load_gs_index may use the wrong GS_BASE
value then leading to unpredictable behavior, e.g. a
triple-fault.

This patch fixes the issue by making sure that load_gs_index
is called only with a valid KERNEL_GS_BASE value loaded in
KVM.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

parent 0b0abeaf

arch/x86/kvm/svm.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1150,8 +1150,8 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
		kvm_load_ldt(svm->host.ldt);
		#ifdef CONFIG_X86_64
		loadsegment(fs, svm->host.fs);
		load_gs_index(svm->host.gs);
		wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
		load_gs_index(svm->host.gs);
		#else
		loadsegment(gs, svm->host.gs);
		#endif