From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28B9EC43381 for ; Mon, 25 Feb 2019 16:37:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED4D820684 for ; Mon, 25 Feb 2019 16:37:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="E+/KriRr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728238AbfBYQhz (ORCPT ); Mon, 25 Feb 2019 11:37:55 -0500 Received: from merlin.infradead.org ([205.233.59.134]:41670 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727950AbfBYQhy (ORCPT ); Mon, 25 Feb 2019 11:37:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=GMwjB0YOeZrQAjzhQaTMpUu1AUhAe5LSmXuz2Kqr6Mg=; b=E+/KriRr/pBGI8/LURR/0dF5ls CvJEjpyzo8yXIK4ItZK7IjYHV6Pt1tsNxtznReceG9Egm6DlUX2LsTnsA/DlSy0qwSMFJy7LjCRTa P1xmmoa1LEOiQ+qVAo91ql+hXPUz1nbIjCuOeDI387LjPAycCJA7K80tXntmLGweWau3A0e3iSZSj JSSiPvRSgNcxD9Ny1HxGkLgiI0xHB/j/6zZjVgAUQ60kGBOVdGq62piyXwLYxojCcTtcOo34PKkSx o5fi9a92p2zcq/wbh03nmIWD9s5Vrz+jHaQaAoKtmWP8NQ3ne/jnQ3rkxFHOsxEKDaPiXUUC0i9Uv J6AgPXKQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gyJGF-0007aA-BE; Mon, 25 Feb 2019 16:37:47 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 050212026BE91; Mon, 25 Feb 2019 17:37:46 +0100 (CET) Date: Mon, 25 Feb 2019 17:37:45 +0100 From: Peter Zijlstra To: Andy Lutomirski Cc: Linus Torvalds , Thomas Gleixner , "H. Peter Anvin" , Julien Thierry , Will Deacon , Ingo Molnar , Catalin Marinas , James Morse , valentin.schneider@arm.com, Brian Gerst , Josh Poimboeuf , Andrew Lutomirski , Borislav Petkov , Denys Vlasenko , LKML Subject: Re: [PATCH 2/6] x86/ia32: Fix ia32_restore_sigcontext AC leak Message-ID: <20190225163745.GF32494@hirez.programming.kicks-ass.net> References: <20190225124330.613028745@infradead.org> <20190225125231.936952143@infradead.org> <20190225161003.GL32477@hirez.programming.kicks-ass.net> <3F83AE74-3F9E-42BB-8F9C-3033F72B3EF5@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3F83AE74-3F9E-42BB-8F9C-3033F72B3EF5@amacapital.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 25, 2019 at 08:29:12AM -0800, Andy Lutomirski wrote: > > diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c > > index 321fe5f5d0e9..e04eeeddcc35 100644 > > --- a/arch/x86/ia32/ia32_signal.c > > +++ b/arch/x86/ia32/ia32_signal.c > > @@ -53,17 +53,16 @@ > > #define GET_SEG(seg) ({ \ > > unsigned short tmp; \ > > get_user_ex(tmp, &sc->seg); \ > > - tmp; \ > > + tmp | 3; \ > > }) > > > > Drop this part. > > > #define COPY_SEG_CPL3(seg) do { \ > > - regs->seg = GET_SEG(seg) | 3; \ > > + regs->seg = GET_SEG(seg); \ > > } while (0) > > And this. > > Unfortunately, whether we want the | 3 varies by segment. For FS and > GS, we definitely don’t want it, since 0 is a common and important > value, and 3 is a deeply screwed up value. (3 is legal to *write* to > GS, and it sticks, but IRET silently changes it to 0, because the > original 386 designers (I assume) confused themselves. > > > > #define RELOAD_SEG(seg) { \ > > - unsigned int pre = GET_SEG(seg); \ > > + unsigned int pre = (seg); \ > > unsigned int cur = get_user_seg(seg); \ > > - pre |= 3; \ And here ? > > if (pre != cur) \ > > set_user_seg(seg, pre); \ > > } Thing is; afaict the current code _always_ does |3 on any GET_SET() result. If you want to change that; I'm fine with that, but lets not do that in this same patch. So then? diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 321fe5f5d0e9..4d5fcd47ab75 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -61,9 +61,8 @@ } while (0) #define RELOAD_SEG(seg) { \ - unsigned int pre = GET_SEG(seg); \ + unsigned int pre = (seg) | 3; \ unsigned int cur = get_user_seg(seg); \ - pre |= 3; \ if (pre != cur) \ set_user_seg(seg, pre); \ } @@ -72,6 +71,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, struct sigcontext_32 __user *sc) { unsigned int tmpflags, err = 0; + u16 gs, fs, es, ds; void __user *buf; u32 tmp; @@ -79,16 +79,10 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, current->restart_block.fn = do_no_restart_syscall; get_user_try { - /* - * Reload fs and gs if they have changed in the signal - * handler. This does not handle long fs/gs base changes in - * the handler, but does not clobber them at least in the - * normal case. - */ - RELOAD_SEG(gs); - RELOAD_SEG(fs); - RELOAD_SEG(ds); - RELOAD_SEG(es); + gs = GET_SEG(gs); + fs = GET_SEG(fs); + ds = GET_SEG(ds); + es = GET_SEG(es); COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx); COPY(dx); COPY(cx); COPY(ip); COPY(ax); @@ -106,6 +100,17 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, buf = compat_ptr(tmp); } get_user_catch(err); + /* + * Reload fs and gs if they have changed in the signal + * handler. This does not handle long fs/gs base changes in + * the handler, but does not clobber them at least in the + * normal case. + */ + RELOAD_SEG(gs); + RELOAD_SEG(fs); + RELOAD_SEG(ds); + RELOAD_SEG(es); + err |= fpu__restore_sig(buf, 1); force_iret();