From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753757AbdIYGOw (ORCPT ); Mon, 25 Sep 2017 02:14:52 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36076 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753195AbdIYGOu (ORCPT ); Mon, 25 Sep 2017 02:14:50 -0400 X-Google-Smtp-Source: AOwi7QBqdpPsWL5PbUMvFlmcemyFInezPIh4yJw2Bs37uz6e2XKZ0npCusRE5ABy6+BtYpxP5LdD4w== Date: Mon, 25 Sep 2017 08:14:45 +0200 From: Ingo Molnar To: Eric Biggers Cc: linux-kernel@vger.kernel.org, Andrew Morton , Andy Lutomirski , Borislav Petkov , Dave Hansen , Fenghua Yu , "H . Peter Anvin" , Linus Torvalds , Oleg Nesterov , Peter Zijlstra , Rik van Riel , Thomas Gleixner , Yu-cheng Yu Subject: Re: [PATCH 03/10] x86/fpu: Use validate_xstate_header() to validate the xstate_header in sanitize_restored_xstate() Message-ID: <20170925061445.uzt5phqebwnvbhcb@gmail.com> References: <20170924105913.9157-1-mingo@kernel.org> <20170924105913.9157-4-mingo@kernel.org> <20170924185147.GA26260@zzz.localdomain> <20170924190242.hsbs7tqhvcalnczt@gmail.com> <20170924200853.GB26260@zzz.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170924200853.GB26260@zzz.localdomain> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Eric Biggers wrote: > On Sun, Sep 24, 2017 at 09:02:42PM +0200, Ingo Molnar wrote: > > > > * Eric Biggers wrote: > > > > > On Sun, Sep 24, 2017 at 12:59:06PM +0200, Ingo Molnar wrote: > > > > @@ -328,10 +331,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > > > > err = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > > > > } else { > > > > err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size); > > > > - > > > > - /* xcomp_bv must be 0 when using uncompacted format */ > > > > - if (!err && fpu->state.xsave.header.xcomp_bv) > > > > - err = -EINVAL; > > > > + if (!err) > > > > + err = validate_xstate_header(&fpu->state.xsave.header); > > > > } > > > > > > > > > > Sorry, this is the buggy part. The problem is that this code runs even if XSAVE > > > isn't being used --- and in that case the state size is 512 bytes or less, so > > > the state doesn't actually include the xstate_header. So > > > validate_xstate_header() was reading out of bounds and seeing invalid values. > > > > > > So I think we need to check use_xsave() here, but it really needs to be in the > > > earlier patch which added the check for just ->xcomp_bv ("x86/fpu: Don't let > > > userspace set bogus xcomp_bv"), not in this one. > > > > > > As far the split of patch 2/3 into these 10 patches, it looks fine (though it > > > suddenly became a *lot* of patches!). One nit: the subject of this one really > > > should say "__fpu__restore_sig()", not "sanitize_restored_xstate()". > > > > > > I can send a fixed series when I have a chance. > > > > Could you please just send the delta patch against the whole tree to fix the bug? > > I'll worry about the patch dependencies and back-merge it to the proper place. > > > > The following diff against tip/master fixes the bug. Note: we *could* check > 'use_xsave()' instead of 'state_size > offsetof(struct xregs_state, header)', > but that might be confusing in the case where we couldn't find the xstate > information in the memory layout and only copy the fxregs_state, since then we'd > actually be validating the xsave_header which was already there, which shouldn't > ever fail. > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index afe54247cf27..fb639e70048f 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -331,7 +331,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > err = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > } else { > err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size); > - if (!err) > + > + if (!err && state_size > offsetof(struct xregs_state, header)) > err = validate_xstate_header(&fpu->state.xsave.header); > } I.e. a better check would be to check that the whole header can be accessed: state_size >= offsetof(struct xregs_state, header) + sizeof(struct xstate_header) Not that there should ever be a 'state_size' that points inside the header - so in the end I back-merged your original (and tested ...) version. Thanks, Ingo