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=-28.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 3C536C4332D for ; Thu, 4 Mar 2021 00:16:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16B1C64EC4 for ; Thu, 4 Mar 2021 00:16:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1392503AbhCDAOw (ORCPT ); Wed, 3 Mar 2021 19:14:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44270 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353065AbhCDADE (ORCPT ); Wed, 3 Mar 2021 19:03:04 -0500 Received: from mail-yb1-xb34.google.com (mail-yb1-xb34.google.com [IPv6:2607:f8b0:4864:20::b34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 78130C0613E5 for ; Wed, 3 Mar 2021 15:34:23 -0800 (PST) Received: by mail-yb1-xb34.google.com with SMTP id m9so26484430ybk.8 for ; Wed, 03 Mar 2021 15:34:23 -0800 (PST) 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=dK3NMZEn6j+LEopfsKHiSKgLCccGDXi0UgAxRfW2Oqc=; b=PmpeEda9EVHOi2NUTA6CQFAIu3OnfUOUQQ1bsO2Wgb4Z1uXp+cFrBBjYJDNIBtXOTs /ckOxfORWw2x+c6lh9BCl/9/Rr3/34Oa+ujJ1Dbtl9cyMTSfcly6z6kzFxCVwEPDAf8X WwfEkSDvKoN4DZwVI3CiTHwAar1bL/8NnTjQ4x/6KFF+nqku5nwb1ciZ7kwpp6idKSnh RB6vdb5nk0v4z94zYx0S/+pkC/AM9E7zatTomJLb6+qeJjTG/2b1x87YaMeyV9M0M70l Xjwi2jPUWCxeQBBWPOfs9MN3LkjS5oQWbUtWkHUgml0L/3ZwnddJea2A85/vRg76WD7o 6u/g== 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=dK3NMZEn6j+LEopfsKHiSKgLCccGDXi0UgAxRfW2Oqc=; b=hht/oiEHhyDhOhJuGzFcdqfqvzjBiegk0hscRRDv9u2tuCF/cwYX5+SAVf2cutBSui 8gYouxX09Rseq43E8Z3z+E6vIqG3e8+tHvtaMRMGPuxmJlFNVH+D9ziVlhVSwXX7LAFZ x4sqBZanilTzG2479yh0mU/pFo+PB8LifTmeGyGvhnlXhCdeyiI3kB4oV5GPTJyP6n10 Uy2FRNVYZtWNHKrIAV8yH14zTzK6iLGJIDvtRjQNkRnqT6hzeApp6Ihf/RemgJX552Lc l46nS+OKGiY6oJjdidTiBkbom6938byMSX8Il/I78kr8MiF2VWyYwWK/c2xzOOWRgY6D Uncg== X-Gm-Message-State: AOAM530I++aTjIYhjxk8a1bnmq6pyAOnbi2vem51395isLV9FtAmTgdq x23gtXF0/hXX44lv1GgTkCHVGeGm6NKCcY0rUOsDcw== X-Google-Smtp-Source: ABdhPJzc/mHrww3IY/9z3+WUQSdSGo89Gggng+nexIlrYjiTSXlmpCbrmm1SF2HqKZOC/kksFNF5jAzISE+d4+AHWE0= X-Received: by 2002:a25:d74b:: with SMTP id o72mr2541368ybg.190.1614814462375; Wed, 03 Mar 2021 15:34:22 -0800 (PST) MIME-Version: 1.0 References: <20210303185807.2160264-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 3 Mar 2021 15:34:11 -0800 Message-ID: Subject: Re: [PATCH v3 1/1] mm/madvise: replace ptrace attach requirement for process_madvise To: Shakeel Butt Cc: Andrew Morton , Jann Horn , Kees Cook , Jeffrey Vander Stoep , Minchan Kim , Michal Hocko , David Rientjes , =?UTF-8?Q?Edgar_Arriaga_Garc=C3=ADa?= , Tim Murray , Florian Weimer , Oleg Nesterov , James Morris , Linux MM , SElinux list , Linux API , linux-security-module , stable , LKML , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt wrote: > > On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan wrote: > > > > process_madvise currently requires ptrace attach capability. > > PTRACE_MODE_ATTACH gives one process complete control over another > > process. It effectively removes the security boundary between the > > two processes (in one direction). Granting ptrace attach capability > > even to a system process is considered dangerous since it creates an > > attack surface. This severely limits the usage of this API. > > The operations process_madvise can perform do not affect the correctness > > of the operation of the target process; they only affect where the data > > is physically located (and therefore, how fast it can be accessed). > > What we want is the ability for one process to influence another process > > in order to optimize performance across the entire system while leaving > > the security boundary intact. > > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > > and CAP_SYS_NICE for influencing process performance. > > > > Cc: stable@vger.kernel.org # 5.10+ > > Signed-off-by: Suren Baghdasaryan > > Reviewed-by: Kees Cook > > Acked-by: Minchan Kim > > Acked-by: David Rientjes > > --- > > changes in v3 > > - Added Reviewed-by: Kees Cook > > - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f458bad476a3358e3a45023789cb7bb9f993 > > - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request > > - cc'ed linux-security-module@vger.kernel.org per James Morris's request > > > > mm/madvise.c | 13 ++++++++++++- > > 1 file changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index df692d2e35d4..01fef79ac761 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > > goto release_task; > > } > > > > - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); > > + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ > > + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); > > if (IS_ERR_OR_NULL(mm)) { > > ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; > > goto release_task; > > } > > > > + /* > > + * Require CAP_SYS_NICE for influencing process performance. Note that > > + * only non-destructive hints are currently supported. > > How is non-destructive defined? Is MADV_DONTNEED non-destructive? Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive. > > > + */ > > + if (!capable(CAP_SYS_NICE)) { > > + ret = -EPERM; > > + goto release_mm; > > + } > > + > > total_len = iov_iter_count(&iter); > > > > while (iov_iter_count(&iter)) { > > @@ -1218,6 +1228,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > > if (ret == 0) > > ret = total_len - iov_iter_count(&iter); > > > > +release_mm: > > mmput(mm); > > release_task: > > put_task_struct(task); > > -- > > 2.30.1.766.gb4fecdf3b7-goog > >