From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227CJyh1vJ8J8SvO04BnDtOtv/XiAolkQ0kWv5cg44vQSiQtCDWg3w2QYLnPCVtHseetxfwI ARC-Seal: i=1; a=rsa-sha256; t=1518113570; cv=none; d=google.com; s=arc-20160816; b=V3BGRr+rxODLSYpRZcZH0wJO+C7lHM2DlGBu63/FrcW3rh0dS47oCS2osR5EBijJKx E+jDVjlP02Un+0vQnEbOep/wYN+v9Gy1XDvplzOF2xCksuyWKCVeZ3i+U2zoMiPKqeMB lM2LlGSpr2V0Ne71yd9zBXpCXRZ7jYnWvuBimiW1HoiIBX6mwN9JxcUqX5HgwBIxm5HR F5kzH/vJrARNHkSdvsOcSn21QWQ41DCm3YD2p9TzI2MLEbJi5rnhx8N7QKQ7n0iZKXpG R6XEFmV/My8mGP9O1pYl7+a5xcyIziSwjqq5hyM6US/2i5eJ7CHvQsPuD5iVOnwH61eH wGrQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=message-id:date:content-transfer-encoding:mime-version:references :in-reply-to:subject:cc:to:from:sender:delivered-to:delivered-to :list-id:list-subscribe:list-unsubscribe:list-help:list-post :precedence:mailing-list:arc-authentication-results; bh=33MGOvvHYPxa+2kSILlN/JSr5kXs6bl0VeCORZuLIrc=; b=dVUgYVp31ZRGafijnCeafJ7CJAFw8y5RmmKHPbZGd7CoX7mRYkpjZAa0crV0o6OkiV Jw29UxXOA6FWye2L94263eQcuIbXUuHllD52M8/UeOwv48rS6LVKkAOEIigEt3ckbWP/ 4bHVTwm4wnwvf4xjGjAJ3YgRb10uQx85rp6dalu5CE4p2mQjdcFErMqgffvtfSa2aE4w 3VfDwF77BT4ArDzSa5rw5hTfo78a3vhyozhj8b6qzPyxmOG6ST0thSn3iSrFG+nCmT2u sLqoeaGJ/YsrSWOMAREvhkzDZt6mH3kft5b4R59IUNKA4DWMsqq5OxZUeHRsabZrI84U sziQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-11658-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-11658-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=vt.edu Authentication-Results: mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-11658-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-11658-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=vt.edu Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: Sender: Valdis Kletnieks From: valdis.kletnieks@vt.edu X-Google-Original-From: Valdis.Kletnieks@vt.edu X-Mailer: exmh version 2.8.0 04/21/2017 with nmh-1.7+dev To: Jann Horn Cc: Matthew Wilcox , linux-mm@kvack.org, Kernel Hardening , kernel list , "Kirill A. Shutemov" Subject: Re: [RFC] Warn the user when they could overflow mapcount In-Reply-To: References: <20180208021112.GB14918@bombadil.infradead.org> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1518112722_2958P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Thu, 08 Feb 2018 12:58:42 -0500 Message-ID: <24367.1518112722@turing-police.cc.vt.edu> X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1591796976786547518?= X-GMAIL-MSGID: =?utf-8?q?1591857455031189496?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: --==_Exmh_1518112722_2958P Content-Type: text/plain; charset=us-ascii On Thu, 08 Feb 2018 03:56:26 +0100, Jann Horn said: > I wouldn't be too surprised if there are more 32-bit overflows that > start being realistic once you put something on the order of terabytes > of memory into one machine, given that refcount_t is 32 bits wide - > for example, the i_count. See > https://bugs.chromium.org/p/project-zero/issues/detail?id=809 for an > example where, given a sufficiently high RLIMIT_MEMLOCK, it was > possible to overflow a 32-bit refcounter on a system with just ~32GiB > of free memory (minimum required to store 2^32 64-bit pointers). > > On systems with RAM on the order of terabytes, it's probably a good > idea to turn on refcount hardening to make issues like that > non-exploitable for now. I have at least 10 systems across the hall that have 3T of RAM on them across our various HPC clusters. So this is indeed no longer a hypothetical issue. --==_Exmh_1518112722_2958P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Comment: Exmh version 2.8.0 04/21/2017 iQEVAwUBWnyP0o0DS38y7CIcAQJvMwgAqINtG3XsiyureZeY7FTqdkwoqxA0BUmM tUkyfbqu/6bfJmdPUOhV4a62wWIULi9xc/yTUcH3Ve/Y71KQVBWfz+QBeeMIihdr Qh8b6SWWL5gViGCj0uw0d8pbwgzmX/PplJSgupP8j4tf3CyQ7FcrIBpB3p8PfocO FINFQ/W8JiCVsTGlgmlcwAlTxTzmNP2EF7JoKp4Ugy/cBpxpN8B35/kawTBWirL4 f2OagdWoDdeyu+XyVEaBhybUuGhGVBnbYGELaaJ5A2uGfPhooVZEMzBDZbFgpesu 9jKlkll5COPF3fozpf6idD5uHYaWGUaYRw5rdH+7+eZ59JdRuYZoiw== =eDZP -----END PGP SIGNATURE----- --==_Exmh_1518112722_2958P--