Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nadav Amit , Paolo Bonzini Subject: [PATCH 3.17 126/319] KVM: x86: Decoding guest instructions which cross page boundary may fail Date: Wed, 12 Nov 2014 10:14:24 +0900 Message-Id: <20141112011013.493463962@linuxfoundation.org> In-Reply-To: <20141112010952.553519040@linuxfoundation.org> References: <20141112010952.553519040@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nadav Amit commit 08da44aedba0f493e10695fa334348a7a4f72eb3 upstream. Once an instruction crosses a page boundary, the size read from the second page disregards the common case that part of the operand resides on the first page. As a result, fetch of long insturctions may fail, and thereby cause the decoding to fail as well. Fixes: 5cfc7e0f5e5e1adf998df94f8e36edaf5d30d38e Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/emulate.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -773,8 +773,10 @@ static int __do_insn_fetch_bytes(struct static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, unsigned size) { - if (unlikely(ctxt->fetch.end - ctxt->fetch.ptr < size)) - return __do_insn_fetch_bytes(ctxt, size); + unsigned done_size = ctxt->fetch.end - ctxt->fetch.ptr; + + if (unlikely(done_size < size)) + return __do_insn_fetch_bytes(ctxt, size - done_size); else return X86EMUL_CONTINUE; }