KVM: VMX: Fix host GDT.LIMIT corruption

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@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6a28d5d95e8fe88f7a5ee7f90ac0b2ae950ec55a..1850cb054d12b22c00b273cf8ed5210db3fbe315 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -130,6 +130,7 @@ 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;
@@ -690,6 +691,7 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
        save_msrs(vmx->guest_msrs, vmx->save_nmsrs);
        load_msrs(vmx->host_msrs, vmx->save_nmsrs);
        reload_host_efer(vmx);
+       load_gdt(&__get_cpu_var(host_gdt));
 }
 
 static void vmx_load_host_state(struct vcpu_vmx *vmx)
@@ -1176,6 +1178,8 @@ static void hardware_enable(void *garbage)
        asm volatile (ASM_VMX_VMXON_RAX
                      : : "a"(&phys_addr), "m"(phys_addr)
                      : "memory", "cc");
+
+       store_gdt(&__get_cpu_var(host_gdt));
 }
 
 static void vmclear_local_vcpus(void)