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=-13.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham 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 B71BCC54FCC for ; Tue, 21 Apr 2020 15:10:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8EBA92068F for ; Tue, 21 Apr 2020 15:10:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="XbPByrKc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729149AbgDUPKO (ORCPT ); Tue, 21 Apr 2020 11:10:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54868 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726018AbgDUPKN (ORCPT ); Tue, 21 Apr 2020 11:10:13 -0400 Received: from mail-lf1-x142.google.com (mail-lf1-x142.google.com [IPv6:2a00:1450:4864:20::142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 158F6C061A10 for ; Tue, 21 Apr 2020 08:10:13 -0700 (PDT) Received: by mail-lf1-x142.google.com with SMTP id l11so11429611lfc.5 for ; Tue, 21 Apr 2020 08:10:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=XNK0e8yf1FrEYvaxfLQv37hJ9f6DqOREqQ/OEs3byWk=; b=XbPByrKcv2Fc3cTT2uQvd0lBB1L7Llj1mV8jtJw+7/p5IMdICaAGGf6LShzjU9krmG Omu1OxI7UC8sJL3plkMvJNbTh+qzjNjk1drRvt1aoR8yEeNn8ILglA6nJuLrhGaXYqVh w8LcASc34gOivyIQKmWmNTudAFpOrC2yJ1SR+p4HItnObTovsoQ3G4UHtyLH7kIv0NEb cEuBC1f41k0zwCGAMgVdVoktWIkQcetGDcQn+WU2z90N/6sisbVV6c3bOw+ZFFrg0CGh Hq72d5fBJfOLSovcq2+I5wMfnDhmr5rhT4jLCY/tCbF6uBxIj5G+LYrF+pcJKN3HAOK6 WA7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XNK0e8yf1FrEYvaxfLQv37hJ9f6DqOREqQ/OEs3byWk=; b=S5aaxienO4wKaqmiqV/IYfy4ZEytLxFMNiXaf5Uej1SIrytmmdvEMPvTonXQAzrG6N +ehosQ4MKHEjWM1VYBnFC8CQ25kE/M/E08XYDEItNALI/RGmGMaUKhGD9zE/PY8LAmbE aNI8MX4nHMm8ffiKOWMQcuYDh1x90Vg+7EXp/D4cc6QDMnseaEo2ntxWgMXzzg4Dryky cLd5sH/rPGDHlg6t8jKsDWVm3a8sIP2nRrjMizjWmudKPXcS86QJBBUg1Esc2zCh5g5q e6crlFzOQPC0md+f7QB5dec12rYWwVeYCOvH+oEXfeBy91C5xBaJ+9Z43o35TgM28pDK UmGQ== X-Gm-Message-State: AGi0PuYMpl3vi9UwaE8Owmgr6I173Y4RKE+DQGQqdeH9Vd31mVX76QQg lmQol/a7uW18Vpy17H1Zvu0/6vKX/kwJ5vh9YwBG5w== X-Google-Smtp-Source: APiQypKLNs/ylG/NH1TDF/1f7YloULLpvIqw0pPPlG6htHD8PvjqTjdNwtVQe7RGogQhs34Lny2XgnJhaBx8k+q+/Sg= X-Received: by 2002:a19:c850:: with SMTP id y77mr13991308lff.45.1587481811207; Tue, 21 Apr 2020 08:10:11 -0700 (PDT) MIME-Version: 1.0 References: <20200419100848.63472-1-glider@google.com> <20200420153352.6682533e794f591dae7aafbc@linux-foundation.org> <202004201540.01C8F82B@keescook> <20200421034249.GB23230@ZenIV.linux.org.uk> In-Reply-To: From: Jann Horn Date: Tue, 21 Apr 2020 17:09:44 +0200 Message-ID: Subject: Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info() To: Alexander Potapenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "the arch/x86 maintainers" , Yu-cheng Yu , Dave Hansen Cc: Al Viro , Kees Cook , Andrew Morton , Alexey Dobriyan , LKML , sunhaoyl@outlook.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +x86 folks (rest of thread is on lore , with original bug report on github ) On Tue, Apr 21, 2020 at 2:54 PM Alexander Potapenko wrote: > On Tue, Apr 21, 2020 at 5:42 AM Al Viro wrote: > > On Mon, Apr 20, 2020 at 03:41:40PM -0700, Kees Cook wrote: > > > On Mon, Apr 20, 2020 at 03:33:52PM -0700, Andrew Morton wrote: > > > > On Sun, 19 Apr 2020 12:08:48 +0200 glider@google.com wrote: > > > > > > > > > KMSAN reported uninitialized data being written to disk when dumping > > > > > core. As a result, several kilobytes of kmalloc memory may be written to > > > > > the core file and then read by a non-privileged user. > > > > > > Ewww. That's been there for 12 years. Did something change in > > > regset_size() or regset->get()? Do you know what leaves the hole? > > > > Not lately and I would also like to hear the details; which regset it is? > > Should be reasonably easy to find - just memset() the damn thing to something > > recognizable, do whatever triggers that KMSAN report and look at that > > resulting coredump. > > > > Seems to be REGSET_XSTATE filled by xstateregs_get(). > Is there a ptrace interface also using that function? It looks to me like the problem KMSAN found is that copy_xstate_to_kernel() will not fill out memory for unused xstates? I think this may have been introduced by commit 91c3dba7dbc1 ("x86/fpu/xstate: Fix PTRACE frames for XSAVES", introduced in v4.8). There seem to be no other functions that reach that path other than coredumping; I think the correct fix would be to change copy_xstate_to_kernel() to always fully initialize the output buffer. The ptrace path uses copy_xstate_to_user(); there, instead of leaking kernel memory to userspace, parts of the userspace buffer are simply not written to at all.