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 1EA5F334374; Mon, 29 Jun 2026 12:51:10 +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=1782737472; cv=none; b=A0v4Hz/4aUg1Vgd+7X/AN7uCmtCckVCGLuEcilwz7EAGxmvWPn8qtURuvnJ0lMH574Y+rM2nOqpcO3LzeqjSvUtBWSwlMRyeLE/uxgnZ6GVb9xAyY3cBccx+KZRq6pdvMxJ4/gp0D71WuhnVUOP8zma6dDeL5bpFrTCvblTJfxA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782737472; c=relaxed/simple; bh=Sf2ujpg/Rw5tZYc9Z4kjo7IjiQSaj0etzo1ySbqjL8c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dPgSXTlSz+AhogXzun7sGHFxVT/63OcW2gj0cdXYWuNdnxBUICf/wbFpOIehRB7Eupri+mBbc1bivONy+AMruBShd24rffT2LR0TFNgsEe/cCufdPp9iX/G1+7qJv6+qLasJeSgBSsHpcHdYjBzCkvM9qgqIyas8nhZ4/wcTBeE= 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=Js7hPGLW; 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="Js7hPGLW" Received: from [IPV6:2601:646:8081:7da1:4462:691a:e05c:b745] ([IPv6:2601:646:8081:7da1:4462:691a:e05c:b745]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 65TCoD8T244601 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 29 Jun 2026 05:50:14 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 65TCoD8T244601 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026062701; t=1782737416; bh=fRdbBuAywd2/yTywAa2lmTsqxPePV+KffkY5n9Y48hM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Js7hPGLWS5LTsb/3bMqBHhoVGIEj0VMpjxMvYFT2YIS6f3nHXeLALfVUDkd+j1wkV nWUug3QAfVgal8LCz0dJ+sOdkzS+uELoC3ObibQVmQU7Joi0u/rYGI9WpA1dIX8YcH Q1Jn+GhyBywHcndGzVYJ+QZ6Zum7Q8wLdpRTMu/8V9g8voVNG41Q8Bjqf/WBLWDW2B h2dbJ1kQ29c77xr5O7maE+enOLuuXL+5UXjMD/MaTsmmkcK25Gpk9a9sQw9lrss5ss 26PFDqL2qXOJRWI+K9ckx1oVcM3YMb4bPv63pNLC6YD30f9ItKquGx5Fmmc/vCeRII C1hgFlSlEGFZQ== Message-ID: <3c4094d8-ae5e-4ffd-b28a-0c10db50296c@zytor.com> Date: Mon, 29 Jun 2026 05:50:08 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vmalloc: widen guard region to defeat ENTER-based stack pivot To: Matthew Wilcox Cc: Xiang Mei , Pedro Falcato , 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 References: <20260626173444.2252041-1-xmei5@asu.edu> <499a4e15-34a4-421b-946a-c855199fdbf9@zytor.com> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026-06-28 21:43, Matthew Wilcox wrote: > On Sun, Jun 28, 2026 at 07:09:37PM -0700, H. Peter Anvin wrote: >> >>> 2) `enter` is not rare since we can take part in the instruction. >> >> This sentence doesn't parse. > > They mean that we can jump into the middle of an instruction, and it is > not rare to see a 'c8' byte in the instruction stream. > OK, I see the point now. The main difference is that ENTER doesn't require a REX prefix, whereas ADD/SUB/LEA do (otherwise it truncates RSP and everything immediately dies as a result of SMAP violations [you are welcome].) This means that an offending bit combination is far less common. -hpa