From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A41B52737E3; Wed, 1 Jul 2026 08:14:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782893693; cv=none; b=A4/pQ62kDWbxIQaXzDI94lCE/0n2fRParD2Ey99gLi/rcnWCvG9S/qgoeDcyFR09z8Tng1++B/29l+pAi8gZEz/w6V45Cxa7Hl0R+/BHNuNAXhtzUkiuxZ574L0SwxYsJhZMBdeFIYdeASmy2Sxti6UH/4DzOU1AXz+h1krVwSU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782893693; c=relaxed/simple; bh=39pxWTxF9Nhuc3P0AQwydW+MAWu+cXbgi7YtbqzrXuU=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=Sg951r4yw+g+aC8xBMxlH8KSFyXuBoUy0BdvDzDR4cD/P1YV8t2L4zn+/cc+epsmRSg3qrOOXuH+1p7ohKP1jPdnAmpFSQvY1Ve+7hWk5L0STEvn1YrK8CitdTNKcWlUEqVEFIL1Db1yM+b6mCCeq/7rkflP4BVOjBIo/frCDSw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=WwYb6t3M; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="WwYb6t3M" Received: from ehlo.thunderbird.net (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 6617wJqg986666 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 1 Jul 2026 00:58:19 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 6617wJqg986666 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026062701; t=1782892700; bh=svsw8bf09g8hVr5lTGfzTsOW2DVBVtdsm1cgrew8gy0=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=WwYb6t3MOkJNASrSHK3PxMbAVLdL9nZ+N2HEetPR//ORAluvuOcgDHW0bq049woTd PYwLvJZ9tEekKWQKgKe11KyOI/RTT0I6fOyzEa7T3nP7p616hJM8BpBlKrVhBryGOs Y/AUVdrqJLlB0LdVD8tqhHXzp/7Go6Ha7etS+gpZmy6IsRx6/1gSjcqYwRTwFo9kj5 eJ4ABsfjsZbiFnaLj1lY/1gk5Kcy7ED/k7Ml6p9R6NBRKXt17lcDdODcQhbe7uwtz2 AWZxnXx1hr+7xuzrBdmOSvXET0xwgMnvk4ootLHSsvX5sJO36PDnQtHORLCqezF3tP Bn5IqhCHAYzrA== Date: Wed, 01 Jul 2026 00:58:12 -0700 From: "H. Peter Anvin" To: Peter Zijlstra , Dave Hansen CC: Xiang Mei , Kees Cook , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, linux-hardening@vger.kernel.org, Uladzislau Rezki , "Gustavo A . R . Silva" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jennifer Miller , Tiffany Bao , Ruoyu Wang , Adam Doupe , Kyle Zeng , Yan Shoshitaishvili Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v2=5D_mm/vmalloc=3A_widen_guard_?= =?US-ASCII?Q?region_to_defeat_ENTER-based_stack_pivot?= User-Agent: K-9 Mail for Android In-Reply-To: <20260701074834.GI49529@noisy.programming.kicks-ass.net> References: <20260629214712.1198680-1-xmei5@asu.edu> <20260701072747.GN48970@noisy.programming.kicks-ass.net> <20260701074834.GI49529@noisy.programming.kicks-ass.net> Message-ID: <8730D74D-6395-4FF4-B9F9-06AFABBF8CDE@zytor.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On July 1, 2026 12:48:34 AM PDT, Peter Zijlstra wr= ote: >On Wed, Jul 01, 2026 at 09:27:47AM +0200, Peter Zijlstra wrote: >> On Mon, Jun 29, 2026 at 03:29:50PM -0700, Dave Hansen wrote: >>=20 >> > But, really, if ENTER is so evil and nobody uses it, shouldn't we jus= t >> > have an MSR bit somewhere to tell the CPU to #UD for it rather than >> > playing these stack games? >>=20 >> For supervisor mode only, I suppose=2E We can't ever get rid of userspa= ce >> ENTER because legacy I suppose=2E But we can make sure the kernel is >> clean=2E >>=20 >> So yeah, having a knob to make supervisor-ENTER trap would be useful I >> suppose=2E > >x86_64-defconfig builds clean with the below :-) > > >diff --git a/tools/objtool/arch/x86/decode=2Ec b/tools/objtool/arch/x86/d= ecode=2Ec >index 1b387d5a195b=2E=2E9e53db863203 100644 >--- a/tools/objtool/arch/x86/decode=2Ec >+++ b/tools/objtool/arch/x86/decode=2Ec >@@ -642,6 +642,10 @@ int arch_decode_instruction(struct objtool_file *fil= e, const struct section *sec >=20 > break; >=20 >+ case 0xc8: >+ WARN("ENTER instruction at %s:%lx", sec->name, offset); >+ break; >+ > case 0xc9: > /* > * leave The problem is that it being a single byte long it can appear in the middl= e of another instruction=2E=20 ENTER was primarily designed for languages with nested local scopes, for w= hich it can do quite a bit of work=2E