From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Erik Rull , Paolo Bonzini Subject: [PATCH 3.10 28/62] KVM: emulate: fix CMPXCHG8B on 32-bit hosts Date: Mon, 16 Mar 2015 15:09:45 +0100 Message-Id: <20150316140934.465633109@linuxfoundation.org> In-Reply-To: <20150316140933.139548981@linuxfoundation.org> References: <20150316140933.139548981@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paolo Bonzini commit 4ff6f8e61eb7f96d3ca535c6d240f863ccd6fb7d upstream. This has been broken for a long time: it broke first in 2.6.35, then was almost fixed in 2.6.36 but this one-liner slipped through the cracks. The bug shows up as an infinite loop in Windows 7 (and newer) boot on 32-bit hosts without EPT. Windows uses CMPXCHG8B to write to page tables, which causes a page fault if running without EPT; the emulator is then called from kvm_mmu_page_fault. The loop then happens if the higher 4 bytes are not 0; the common case for this is that the NX bit (bit 63) is 1. Fixes: 6550e1f165f384f3a46b60a1be9aba4bc3c2adad Fixes: 16518d5ada690643453eb0aef3cc7841d3623c2d Reported-by: Erik Rull Tested-by: Erik Rull Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/emulate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4732,7 +4732,8 @@ int x86_emulate_insn(struct x86_emulate_ if (rc != X86EMUL_CONTINUE) goto done; } - ctxt->dst.orig_val = ctxt->dst.val; + /* Copy full 64-bit value for CMPXCHG8B. */ + ctxt->dst.orig_val64 = ctxt->dst.val64; special_insn: