From: Thomas Gleixner <tglx@linutronix.de>
Subject: KVM: SVM: Move spec control call after restore of GS
Patch-mainline: v4.17-rc7
Git-commit: 15e6c22fd8e5a42c5ed6d487b7c9fe44c2517765
References: bsc#1087082 CVE-2018-3639

svm_vcpu_run() invokes x86_spec_ctrl_restore_host() after VMEXIT, but
before the host GS is restored. x86_spec_ctrl_restore_host() uses 'current'
to determine the host SSBD state of the thread. 'current' is GS based, but
host GS is not yet restored and the access causes a triple fault.

Move the call after the host GS restore.

Fixes: 5cf687548705 ("x86/bugs, KVM: Support the combination of guest and host IBRS")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kvm/svm.c |   24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5449,6 +5449,18 @@ static void svm_vcpu_run(struct kvm_vcpu
 #endif
 		);
 
+	/* Eliminate branch target predictions from guest mode */
+	vmexit_fill_RSB();
+
+#ifdef CONFIG_X86_64
+	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
+#else
+	loadsegment(fs, svm->host.fs);
+#ifndef CONFIG_X86_32_LAZY_GS
+	loadsegment(gs, svm->host.gs);
+#endif
+#endif
+
 	/*
 	 * We do not use IBRS in the kernel. If this vCPU has used the
 	 * SPEC_CTRL MSR it may have left it on; save the value and
@@ -5469,18 +5481,6 @@ static void svm_vcpu_run(struct kvm_vcpu
 
 	x86_spec_ctrl_restore_host(svm->spec_ctrl);
 
-	/* Eliminate branch target predictions from guest mode */
-	vmexit_fill_RSB();
-
-#ifdef CONFIG_X86_64
-	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
-#else
-	loadsegment(fs, svm->host.fs);
-#ifndef CONFIG_X86_32_LAZY_GS
-	loadsegment(gs, svm->host.gs);
-#endif
-#endif
-
 	reload_tss(vcpu);
 
 	local_irq_disable();