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Subject[151/289] KVM: VMX: Fix host userspace gsbase corruption
2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Avi Kivity <avi@redhat.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/kvm/vmx.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -828,10 +828,9 @@ static void vmx_save_host_state(struct k
#endif

#ifdef CONFIG_X86_64
- if (is_long_mode(&vmx->vcpu)) {
- rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
+ rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
+ if (is_long_mode(&vmx->vcpu))
wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
- }
#endif
for (i = 0; i < vmx->save_nmsrs; ++i)
kvm_set_shared_msr(vmx->guest_msrs[i].index,
@@ -846,11 +845,14 @@ static void __vmx_load_host_state(struct

++vmx->vcpu.stat.host_state_reload;
vmx->host_state.loaded = 0;
+#ifdef CONFIG_X86_64
+ if (is_long_mode(&vmx->vcpu))
+ rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
+#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
@@ -859,10 +861,7 @@ static void __vmx_load_host_state(struct
loadsegment(fs, vmx->host_state.fs_sel);
reload_tss();
#ifdef CONFIG_X86_64
- if (is_long_mode(&vmx->vcpu)) {
- rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
- wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
- }
+ wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
#endif
if (current_thread_info()->status & TS_USEDFPU)
clts();



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