KVM: VMX: Fix host userspace gsbase corruption

commit c8770e7ba63bb5dd8fe5f9d251275a8fa717fb78 upstream.

We now use load_gs_index() to load gs safely; unfortunately this also
changes MSR_KERNEL_GS_BASE, which we managed separately.  This resulted
in confusion and breakage running 32-bit host userspace on a 64-bit kernel.

Fix by
- saving guest MSR_KERNEL_GS_BASE before we we reload the host's gs
- doing the host save/load unconditionally, instead of only when in guest
  long mode

Things can be cleaned up further, but this is the minmal fix for now.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
[bwh: Backport to 2.6.32]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d00c64344ee60f07e23639b6ca71e9ea84c1f399..d9c4fb6f0ff37545f95c29c520c3c9dde17c06c5 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -654,10 +654,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
 #endif
 
 #ifdef CONFIG_X86_64
-       if (is_long_mode(&vmx->vcpu))
-               save_msrs(vmx->host_msrs +
-                         vmx->msr_offset_kernel_gs_base, 1);
-
+       save_msrs(vmx->host_msrs + vmx->msr_offset_kernel_gs_base, 1);
 #endif
        load_msrs(vmx->guest_msrs, vmx->save_nmsrs);
        load_transition_efer(vmx);
@@ -672,17 +669,26 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
        vmx->host_state.loaded = 0;
        if (vmx->host_state.fs_reload_needed)
                loadsegment(fs, vmx->host_state.fs_sel);
+#ifdef CONFIG_X86_64
+       if (is_long_mode(&vmx->vcpu))
+               save_msrs(vmx->guest_msrs + vmx->msr_offset_kernel_gs_base, 1);
+#endif
        if (vmx->host_state.gs_ldt_reload_needed) {
                kvm_load_ldt(vmx->host_state.ldt_sel);
 #ifdef CONFIG_X86_64
                load_gs_index(vmx->host_state.gs_sel);
-               wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
 #else
                loadsegment(gs, vmx->host_state.gs_sel);
 #endif
        }
        reload_tss();
+#ifdef CONFIG_X86_64
+       save_msrs(vmx->guest_msrs, vmx->msr_offset_kernel_gs_base);
+       save_msrs(vmx->guest_msrs + vmx->msr_offset_kernel_gs_base + 1,
+                 vmx->save_nmsrs - vmx->msr_offset_kernel_gs_base - 1);
+#else
        save_msrs(vmx->guest_msrs, vmx->save_nmsrs);
+#endif
        load_msrs(vmx->host_msrs, vmx->save_nmsrs);
        reload_host_efer(vmx);
        load_gdt(&__get_cpu_var(host_gdt));