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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F97DC48BC4 for ; Sun, 18 Feb 2024 00:26:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 906E06B009E; Sat, 17 Feb 2024 19:26:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8B79C6B009F; Sat, 17 Feb 2024 19:26:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7A63A6B00A0; Sat, 17 Feb 2024 19:26:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 66A9F6B009E for ; Sat, 17 Feb 2024 19:26:48 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id DF1AD80375 for ; Sun, 18 Feb 2024 00:26:47 +0000 (UTC) X-FDA: 81803034054.01.6436AD2 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) by imf18.hostedemail.com (Postfix) with ESMTP id 8C2C01C0009 for ; Sun, 18 Feb 2024 00:26:45 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=zytor.com header.s=2024021201 header.b="Kbh/cWTs"; spf=pass (imf18.hostedemail.com: domain of hpa@zytor.com designates 198.137.202.136 as permitted sender) smtp.mailfrom=hpa@zytor.com; dmarc=pass (policy=none) header.from=zytor.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1708216006; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Wz3l09giQfTSL1YwWsrN6DHEZxbftRXxZ+FPELlf150=; b=lbgwNGHlbENw2Jh0oSttx76oJVbg/kzLzN/Mypw4lFODq72uzEnAJtS1tSbdWJkNfJbxE7 kL44Egow/7kFn3VqhKriTWS3Azn6lYO89M9ZSwSIOJ8KWEa85Kf74Nd5E86ljSj9AlxqH7 5hVvEVloIWklh7VAm6YBFw91P0Dh7wY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1708216006; a=rsa-sha256; cv=none; b=SyFIZHyYLdqQrmXsQ+bhx0bugG7C2dS2kUajeReNiQEcGu/c5nyQ0o5QsWF62hi4V+ICin pqbTRiN43sotVyhrVTWEzZL770UZNcMoizw3yoWdjjpY7IQ1EnzQUqWSKmh68ST4mFVdH6 JLpiY837r5W7IOV/T24csVJ0c2lc4Ts= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=zytor.com header.s=2024021201 header.b="Kbh/cWTs"; spf=pass (imf18.hostedemail.com: domain of hpa@zytor.com designates 198.137.202.136 as permitted sender) smtp.mailfrom=hpa@zytor.com; dmarc=pass (policy=none) header.from=zytor.com Received: from [127.0.0.1] ([76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.17.2/8.17.1) with ESMTPSA id 41I0PcJe2642444 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Sat, 17 Feb 2024 16:25:39 -0800 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 41I0PcJe2642444 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2024021201; t=1708215944; bh=Wz3l09giQfTSL1YwWsrN6DHEZxbftRXxZ+FPELlf150=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=Kbh/cWTs4TZxrYFDQ9PGa9IsSYuA1vHWzgIsTR0kvi4sW/bys585nuFqikL0TP5gm HKIVOVqbT7JBgMSPQTIwCyqhkiwtXimEAmjOXHjR+2553XQJaMLSzYstWWUWnS4bKN dQOpwm5HzNuMPAIWbCXZ1VCkmdcz6uzIgYOMlj5+Cn11b+VeVfNQY6lnCMeyDdLuuS Ye2WBh6HLbJT67nCtUY3geuu7PCBMFHE/c0FI1Bv7dC7naHq0HkUbcVGJabT880svv Wr8a2dA16Nlv2/Q86qDi2U+JKHTIgZbdXPgEurZBZy98nZMptUmWwHxqFcf1ctQEKg 2lKStlO9LtM6A== Date: Sat, 17 Feb 2024 16:25:33 -0800 From: "H. Peter Anvin" To: Kees Cook , Jiri Kosina CC: Geert Uytterhoeven , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Peter Zijlstra , Qi Zheng , Alexandre Ghiti , Al Viro , Christian Brauner , Jan Kara , Eric Biederman , Christophe Leroy , Josh Poimboeuf , "Kirill A. Shutemov" , Rick Edgecombe , Brian Gerst , Bjorn Helgaas , Tony Battersby , linux-kernel@vger.kernel.org, y0un9n132@gmail.com, x86@kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 0/2] Adjust brk randomness User-Agent: K-9 Mail for Android In-Reply-To: <20240217062035.work.493-kees@kernel.org> References: <20240217062035.work.493-kees@kernel.org> Message-ID: <05E12A71-D8A4-4E6D-9C9D-024251C1BDC7@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 8C2C01C0009 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: pch16mjoxwsh9yi75j9ohkth9pt36ntq X-HE-Tag: 1708216005-726201 X-HE-Meta: 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 ORVrdIcE qUFT4tutC3JOV+4uDwQOLQPBzY9QcSWPmNZSct5jUKcq6ii9JrDuecb4ROlyzydbh9reqH7HyaRwUfDSKiqEb2J8C/29DjvBxS2pFYMTbQx6jiOTxy84xV95j+oTcnVCfOSF0E9cKsA8wzQVgYHDCVgwTNX1aKU4neq9ZG76GPAbeOgRu54li4h7P3CGC7DGYG5q4VKmOhAU9inkatQxiGXVRzNVSGdwKlZFO93UYA7kdDuXBAhMAZyzUdybhwmx+QwVgx+Gs9EO1iyZOCo3YXIb0UnQ93WY7Ye0zuwtfq1F/lvHfuLVV4P2J3/ipTuRnyh3jeW64/ze/aWU= 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: List-Subscribe: List-Unsubscribe: On February 16, 2024 10:25:42 PM PST, Kees Cook w= rote: >Hi, > >It was recently pointed out[1] that x86_64 brk entropy was not great, >and that on all architectures the brk can (when the random offset is 0) >be immediately adjacent to =2Ebss, leaving no gap that could stop linear >overflows from the =2Ebss=2E Address both issues=2E > >-Kees > >Link: https://lore=2Ekernel=2Eorg/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmu= s=3DdzOUG5E4gV7ayCbu0MPJTZzWkw@mail=2Egmail=2Ecom [1] > >Kees Cook (2): > x86: Increase brk randomness entropy on x86_64 > binfmt_elf: Leave a gap between =2Ebss and brk > > arch/x86/kernel/process=2Ec | 5 ++++- > fs/binfmt_elf=2Ec | 3 +++ > 2 files changed, 7 insertions(+), 1 deletion(-) > Why do we even have the brk, or perhaps more importantly, why do we use it= ? Is there any reason whatsoever why glibc uses brk instead of mmap to her = heap memory? I thought the base of the brk wasn't even known to userspace other than in= the form of the image end=2E=2E=2E