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>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b372a7557c16c7d8391fffafdf0b1c74b49c4822..9da95b9daf8deb83af606ae0fffb73f7fab74ff2 100644 (file)
--- 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)