From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756194AbaIZWAo (ORCPT ); Fri, 26 Sep 2014 18:00:44 -0400 Received: from mail-oi0-f50.google.com ([209.85.218.50]:54662 "EHLO mail-oi0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755148AbaIZWAn (ORCPT ); Fri, 26 Sep 2014 18:00:43 -0400 Date: Fri, 26 Sep 2014 17:00:41 -0500 From: Chuck Ebbert To: Anish Bhatt Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, sebastian@fds-team.de, Linus Torvalds Subject: Re: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry Message-ID: <20140926170041.700f44bd@as> In-Reply-To: <1411674171-24442-1-git-send-email-anish@chelsio.com> References: <1411674171-24442-1-git-send-email-anish@chelsio.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 25 Sep 2014 12:42:51 -0700 Anish Bhatt wrote: > The MSR_SYSCALL_MASK, which is responsible for clearing specific EFLAGS on > syscall entry, should also clear the nested task (NT) flag to be safe from > userspace injection. Without this fix the application segmentation > faults on syscall return because of the changed meaning of the IRET > instruction. > > Further details can be seen here https://bugs.winehq.org/show_bug.cgi?id=33275 > > Signed-off-by: Anish Bhatt > Signed-off-by: Sebastian Lackner > --- > arch/x86/kernel/cpu/common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index e4ab2b4..3126558 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -1184,7 +1184,7 @@ void syscall_init(void) > /* Flags to clear on syscall */ > wrmsrl(MSR_SYSCALL_MASK, > X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF| > - X86_EFLAGS_IOPL|X86_EFLAGS_AC); > + X86_EFLAGS_IOPL|X86_EFLAGS_AC|X86_EFLAGS_NT); > } > > /* I don't get it. Why isn't this patch acceptable, at least on x86-64 where NT is never valid? Bueller?