KVM: x86: fix RSM into 64-bit protected mode

In order to get into 64-bit protected mode, you need to enable
paging while EFER.LMA=1.  For this to work, CS.L must be 0.
Currently, we load the segments before CR0 and CR4, which means
that if RSM returns into 64-bit protected mode CS.L is already 1
and everything breaks.

Luckily, CS.L=0 is always the case when executing RSM, because it
is forbidden to execute RSM from 64-bit protected mode.  Hence it
is enough to load CR0 and CR4 first, and only then the segments.

Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b372a7557c16..9da95b9daf8d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2418,7 +2418,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
         u64 val, cr0, cr4;
         u32 base3;
         u16 selector;
-        int i;
+        int i, r;
 
         for (i = 0; i < 16; i++)
                 *reg_write(ctxt, i) = GET_SMSTATE(u64, smbase, 0x7ff8 - i * 8);
@@ -2460,13 +2460,17 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
         dt.address =                GET_SMSTATE(u64, smbase, 0x7e68);
         ctxt->ops->set_gdt(ctxt, &dt);
 
+        r = rsm_enter_protected_mode(ctxt, cr0, cr4);
+        if (r != X86EMUL_CONTINUE)
+                return r;
+
         for (i = 0; i < 6; i++) {
-                int r = rsm_load_seg_64(ctxt, smbase, i);
+                r = rsm_load_seg_64(ctxt, smbase, i);
                 if (r != X86EMUL_CONTINUE)
                         return r;
         }
 
-        return rsm_enter_protected_mode(ctxt, cr0, cr4);
+        return X86EMUL_CONTINUE;
 }
 
 static int em_rsm(struct x86_emulate_ctxt *ctxt)