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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 80747C4727D for ; Mon, 21 Sep 2020 23:48:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EB25523A75 for ; Mon, 21 Sep 2020 23:48:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="goDxIMoD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB25523A75 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 10D7A900007; Mon, 21 Sep 2020 19:48:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0BE89900004; Mon, 21 Sep 2020 19:48:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EA134900007; Mon, 21 Sep 2020 19:48:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0201.hostedemail.com [216.40.44.201]) by kanga.kvack.org (Postfix) with ESMTP id C9F9E900004 for ; Mon, 21 Sep 2020 19:48:40 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 8C33E8249980 for ; Mon, 21 Sep 2020 23:48:40 +0000 (UTC) X-FDA: 77288710800.05.bikes32_48062f727149 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin05.hostedemail.com (Postfix) with ESMTP id 68F9618012CDA for ; Mon, 21 Sep 2020 23:48:40 +0000 (UTC) X-HE-Tag: bikes32_48062f727149 X-Filterd-Recvd-Size: 7927 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 21 Sep 2020 23:48:39 +0000 (UTC) Received: from mail-wr1-f52.google.com (mail-wr1-f52.google.com [209.85.221.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8BC1823A9F for ; Mon, 21 Sep 2020 23:48:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600732118; bh=N8vHQdEHpTHWvUHKpDbNH8Yi1jVK5l/yl5V+P+NE0OA=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=goDxIMoDoxVa3C64VsVsoO1jj5SNv4S6MzZHZ98rF+dlRwaM2zylky7OMs58V0cIt 0k34+7+qqV1O1on10uR7KTin37l5HHeADO5pXJZJTKNV4jiznZr/kCqEdpy6SoWJMv J+loS6sIAobeIhC7PKoJMovzXnqu/F07k7RzKvZA= Received: by mail-wr1-f52.google.com with SMTP id e16so15028681wrm.2 for ; Mon, 21 Sep 2020 16:48:38 -0700 (PDT) X-Gm-Message-State: AOAM532aFARTJVOIdjI1SPAPIkB3oH3XAq9UZc+ho6Z685LVTdRbGxic 3jk220ZxPabuHuKT1DskTCLncV/1VX68xMWDDBTFrg== X-Google-Smtp-Source: ABdhPJzngS+LJRRhcziEyC3Eee4FojJ0Xz7OhABh4eqwGzQo/447WGnYoKx4dZhgKZSGTGYlukUJFQ1u+OQ1i1Jxyaw= X-Received: by 2002:a5d:6a47:: with SMTP id t7mr2138226wrw.75.1600732116993; Mon, 21 Sep 2020 16:48:36 -0700 (PDT) MIME-Version: 1.0 References: <20200918192312.25978-1-yu-cheng.yu@intel.com> <20200918192312.25978-9-yu-cheng.yu@intel.com> <24718de58ab7bc6d7288c58d3567ad802eeb6542.camel@intel.com> In-Reply-To: <24718de58ab7bc6d7288c58d3567ad802eeb6542.camel@intel.com> From: Andy Lutomirski Date: Mon, 21 Sep 2020 16:48:25 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled To: Yu-cheng Yu Cc: Andy Lutomirski , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , "open list:DOCUMENTATION" , Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 21, 2020 at 3:37 PM Yu-cheng Yu wrote: > > On Mon, 2020-09-21 at 09:22 -0700, Yu, Yu-cheng wrote: > > On 9/18/2020 5:11 PM, Andy Lutomirski wrote: > > > On Fri, Sep 18, 2020 at 12:23 PM Yu-cheng Yu wrote: > > > > Emulation of the legacy vsyscall page is required by some programs > > > > built before 2013. Newer programs after 2013 don't use it. > > > > Disable vsyscall emulation when Control-flow Enforcement (CET) is > > > > enabled to enhance security. > > > > > > > > Signed-off-by: Yu-cheng Yu > [...] > > > > > > Nope, try again. Having IBT on does *not* mean that every library in > > > the process knows that we have indirect branch tracking. The legacy > > > bitmap exists for a reason. Also, I want a way to flag programs as > > > not using the vsyscall page, but that flag should not be called CET. > > > And a process with vsyscalls off should not be able to read the > > > vsyscall page, and /proc/self/maps should be correct. > > > > > > So you have some choices: > > > > > > 1. Drop this patch and make it work. > > > > > > 2. Add a real per-process vsyscall control. Either make it depend on > > > vsyscall=xonly and wire it up correctly or actually make it work > > > correctly with vsyscall=emulate. > > > > > > NAK to any hacks in this space. Do it right or don't do it at all. > > > > > > > We can drop this patch, and bring back the previous patch that fixes up > > shadow stack and ibt. That makes vsyscall emulation work correctly, and > > does not force the application to do anything different from what is > > working now. I will post the previous patch as a reply to this thread > > so that people can make comments on it. > > > > Yu-cheng > > Here is the patch: > > ------ > > From dfdee39c795ee5dcee2c77f6ba344a61f4d8124b Mon Sep 17 00:00:00 2001 > From: Yu-cheng Yu > Date: Thu, 29 Nov 2018 14:15:38 -0800 > Subject: [PATCH 34/43] x86/vsyscall/64: Fixup Shadow Stack and Indirect Branch > Tracking for vsyscall emulation > > Vsyscall entry points are effectively branch targets. Mark them with > ENDBR64 opcodes. When emulating the RET instruction, unwind the shadow > stack and reset IBT state machine. > > Signed-off-by: Yu-cheng Yu > --- > arch/x86/entry/vsyscall/vsyscall_64.c | 29 +++++++++++++++++++++++ > arch/x86/entry/vsyscall/vsyscall_emu_64.S | 9 +++++++ > arch/x86/entry/vsyscall/vsyscall_trace.h | 1 + > 3 files changed, 39 insertions(+) > > diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c > b/arch/x86/entry/vsyscall/vsyscall_64.c > index 44c33103a955..0131c9f7f9c5 100644 > --- a/arch/x86/entry/vsyscall/vsyscall_64.c > +++ b/arch/x86/entry/vsyscall/vsyscall_64.c > @@ -38,6 +38,9 @@ > #include > #include > #include > +#include > +#include > +#include > > #define CREATE_TRACE_POINTS > #include "vsyscall_trace.h" > @@ -286,6 +289,32 @@ bool emulate_vsyscall(unsigned long error_code, > /* Emulate a ret instruction. */ > regs->ip = caller; > regs->sp += 8; > + > + if (current->thread.cet.shstk_size || > + current->thread.cet.ibt_enabled) { > + u64 r; > + > + fpregs_lock(); > + if (test_thread_flag(TIF_NEED_FPU_LOAD)) > + __fpregs_load_activate(); Wouldn't this be nicer if you operated on the memory image, not the registers? > + > +#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER > + /* Fixup branch tracking */ > + if (current->thread.cet.ibt_enabled) { > + rdmsrl(MSR_IA32_U_CET, r); > + wrmsrl(MSR_IA32_U_CET, r & ~CET_WAIT_ENDBR); > + } > +#endif Seems reasonable on first glance. > + > +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER > + /* Unwind shadow stack. */ > + if (current->thread.cet.shstk_size) { > + rdmsrl(MSR_IA32_PL3_SSP, r); > + wrmsrl(MSR_IA32_PL3_SSP, r + 8); > + } > +#endif What happens if the result is noncanonical? A quick skim of the SDM didn't find anything. This latter issue goes away if you operate on the memory image, though -- writing a bogus value is just fine, since the FP restore will handle it.