Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752272AbcD2Wrq (ORCPT ); Fri, 29 Apr 2016 18:47:46 -0400 Received: from mga11.intel.com ([192.55.52.93]:8040 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800AbcD2Wrp (ORCPT ); Fri, 29 Apr 2016 18:47:45 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,553,1455004800"; d="scan'208";a="965694238" Date: Fri, 29 Apr 2016 15:43:39 -0700 From: Yu-cheng Yu To: Dave Hansen Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, Andy Lutomirski , Borislav Petkov , Sai Praneeth Prakhya , "Ravi V. Shankar" , Fenghua Yu Subject: Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly Message-ID: <20160429224338.GA15757@test-lenovo> References: <5723BF63.2000100@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5723BF63.2000100@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1263 Lines: 30 On Fri, Apr 29, 2016 at 01:09:07PM -0700, Dave Hansen wrote: > On 03/04/2016 10:12 AM, Yu-cheng Yu wrote: > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > > index 0fbf60c..09945f1 100644 > > --- a/arch/x86/kernel/fpu/signal.c > > +++ b/arch/x86/kernel/fpu/signal.c > > @@ -130,6 +130,45 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf) > > return err; > > } > > > > +static int may_copy_fpregs_to_sigframe(void) > > +{ > > + /* > > + * In signal handling path, the kernel already checks if > > + * FPU instructions have been used before it calls > > + * copy_fpstate_to_sigframe(). We check this here again > > + * to detect any potential mis-use and saving invalid > > + * register values directly to a signal frame. > > + */ > > + WARN_ONCE(!current->thread.fpu.fpstate_active, > > + "direct FPU save with no math use\n"); > > This is probably an OK check for this _particular_ context (since this > context is all ready to copy_to_user() the fpu state). But is it good > generally? Why couldn't you have a !fpstate_active thread that _was_ > fpregs_active? > > Such a thread _could_ do a direct XSAVE with no issues. But it won't come to this function unless fpstate_active is ture?