KVM: SVM: Move spec control call after restore of GS

commit 15e6c22fd8e5a42c5ed6d487b7c9fe44c2517765 upstream.

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: 885f82bfbc6f x86/process: Allow runtime control of Speculative Store Bypass
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 541fb5d9152c713e12334a9b661941174587f193..e074cb7b6486ddbfe0da2fe62c14f8c07123e0ae 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4061,6 +4061,18 @@ static void svm_vcpu_run(struct kvm_vcpu *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
@@ -4081,18 +4093,6 @@ static void svm_vcpu_run(struct kvm_vcpu *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();