[PATCH v2 05/11] KVM: x86: emulator: update the emulation mode after CR0 write

Maxim Levitsky
2022-06-21T15:09:48Z

CR0.PE toggles real/protected mode, thus its update
should update the emulation 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>
---
arch/x86/kvm/emulate.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6f4632babc4cd8..002687d17f9364 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3659,11 +3659,22 @@ 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 */
+ r = update_emulation_mode(ctxt);
+ if (r != X86EMUL_CONTINUE)
+ return r;
+ }
+
return X86EMUL_CONTINUE;
}

--
2.26.3