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Subject[046/127] KVM: VMX: Fix host userspace gsbase corruption
2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

From: Ben Hutchings <ben@decadent.org.uk>

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>

---
arch/x86/kvm/vmx.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -654,10 +654,7 @@ static void vmx_save_host_state(struct k
#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
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));



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