[34-longterm 235/260] KVM: VMX: Fix host GDT.LIMIT corruption

[Paul Gortmaker]

From: Avi Kivity <avi@xxxxxxxxxx>

commit 3444d7da1839b851eefedd372978d8a982316c36 upstream.

vmx does not restore GDT.LIMIT to the host value, instead it sets it to 64KB.
This means host userspace can learn a few bits of host memory.

Fix by reloading GDTR when we load other host state.

Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3c86c42..11db911 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -170,6 +170,7 @@ static u64 construct_eptp(unsigned long root_hpa);
 static DEFINE_PER_CPU(struct vmcs *, vmxarea);
 static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
 static DEFINE_PER_CPU(struct list_head, vcpus_on_cpu);
+static DEFINE_PER_CPU(struct desc_ptr, host_gdt);
 
 static unsigned long *vmx_io_bitmap_a;
 static unsigned long *vmx_io_bitmap_b;
@@ -717,6 +718,7 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
 		wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
 	}
 #endif
+	load_gdt(&__get_cpu_var(host_gdt));
 }
 
 static void vmx_load_host_state(struct vcpu_vmx *vmx)
@@ -1218,6 +1220,8 @@ static int hardware_enable(void *garbage)
 
 	ept_sync_global();
 
+	store_gdt(&__get_cpu_var(host_gdt));
+
 	return 0;
 }
 
-- 
1.7.3.3

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