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 8806CC4332B for ; Thu, 4 Mar 2021 01:20:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4774C64FB3 for ; Thu, 4 Mar 2021 01:20:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235667AbhCDBT5 (ORCPT ); Wed, 3 Mar 2021 20:19:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33232 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239181AbhCDBTG (ORCPT ); Wed, 3 Mar 2021 20:19:06 -0500 Received: from mail-yb1-xb2d.google.com (mail-yb1-xb2d.google.com [IPv6:2607:f8b0:4864:20::b2d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69DCFC0613D7 for ; Wed, 3 Mar 2021 17:17:56 -0800 (PST) Received: by mail-yb1-xb2d.google.com with SMTP id h82so12914799ybc.13 for ; Wed, 03 Mar 2021 17:17:56 -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=cDGMmdlKM20UbxSk1D5HECStpUJywJgGf1k2Ph58Sv4=; b=Biwa5C9LBzhQgtedUPAK6nj6XvZwKukqS173MEMYHs8EnBOalCdRzddBpT28z/s4M1 C8jiWaLWV/QeBcbnLZuTVpheAwE2sHqBop6iq/q/mBXyF34ewhHxWbtn+X0gHy3oR7U9 upFl7iFJXW9cxs22jmCAvu5tsd8n2xCN4g7YTATbMYcezrCQ5pwIF8GgMsOfhUHej2M9 NvjUIMacn8ixwWQreNum7fI/cxxMiNbKqyDmZ4BiA2UNW9f61p6vQqOKHOtVPqzoyfo5 C32W6Q8M4FOHGBaX5TSrasEPYyOGQLtl8k2JNOOYsoBsLWPWoGB9e1hMX/uuTzqrC7pF TuAA== 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=cDGMmdlKM20UbxSk1D5HECStpUJywJgGf1k2Ph58Sv4=; b=dCKg/S9g3ZKnHQtfoBRS2Djz51ZK19K8T3Gfegi8ZoPYdn6/iaX9w117Z0rq0ctPTC aQpfmxaNQ1zs262l+mx4RMwq0GxcZkuZV3ZH/vx91RM9gGOCfnemHNTOBYzLM78c7DOh CDQ5QJerZflqMzhEJxmkaXf9pu2Yqv5+l+7NQIsjU48lCo8+NtyP0e+5/mRu0Chw8lSK sMPW6xKPrDg4gcn3PjdlRkRUVo/FMecGHOPwVXkFbES3OfWlaiNcAg/3uusHB2pa9uE2 IqUDYRasT+xtF6v8BIC/WK5GmTgPgg8MuEqlgwCQ7bmCsieNnuuefD268cexk2zRw84J 7TTg== X-Gm-Message-State: AOAM530BGrGYSDXKqmYvvC7RC/gD/7U6Pj3AEyW2AGq3gnsLR8r6q5KQ q0BRTABlX5azuaVO4mrUtzPxgwhggxKZf16LVly6Xw== X-Google-Smtp-Source: ABdhPJyfPshyKfeDIOoqAVg5Fwk8zLy1gznd2y9ophif2UxaiMhTBt3pbqxOJ6plYf+5MPVAog6sGYQXCN5R/Gnxis0= X-Received: by 2002:a5b:751:: with SMTP id s17mr3016364ybq.111.1614820675298; Wed, 03 Mar 2021 17:17:55 -0800 (PST) MIME-Version: 1.0 References: <20210303185807.2160264-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 3 Mar 2021 17:17:44 -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 4:04 PM Shakeel Butt wrote: > > On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan wrote: > > > > 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. > > > > There is a plan to support MADV_DONTNEED for this syscall. Do we need > to change these access checks again with that support? I think so. Destructive hints affect the data, so we will probably need stricter checks for those hints.