KVM: x86: emulator: update the emulation mode after CR0 write

Update the emulation mode when handling writes to CR0, because
toggling CR0.PE switches between Real and Protected Mode, and toggling
CR0.PG when EFER.LME=1 switches between Long and Protected Mode.

This is likely a benign bug because there is no writeback of state,
other than the RIP increment, and when toggling CR0.PE, the CPU has
to execute code from a very low memory address.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20221025124741.228045-14-mlevitsk@redhat.com>
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 33385ebae1004403d17a980940d8d905c9210aac..2954c046740bfbf1fe270f79d1fa4bfbdb602cd8 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3641,11 +3641,25 @@ static int em_movbe(struct x86_emulate_ctxt *ctxt)
 
 static int em_cr_write(struct x86_emulate_ctxt *ctxt)
 {
-       if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val))
+       int cr_num = ctxt->modrm_reg;
+       int r;
+
+       if (ctxt->ops->set_cr(ctxt, cr_num, ctxt->src.val))
                return emulate_gp(ctxt, 0);
 
        /* Disable writeback. */
        ctxt->dst.type = OP_NONE;
+
+       if (cr_num == 0) {
+               /*
+                * CR0 write might have updated CR0.PE and/or CR0.PG
+                * which can affect the cpu's execution mode.
+                */
+               r = emulator_recalc_and_set_mode(ctxt);
+               if (r != X86EMUL_CONTINUE)
+                       return r;
+       }
+
        return X86EMUL_CONTINUE;
 }