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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 B504DC43381 for ; Wed, 20 Jan 2021 13:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DA1823371 for ; Wed, 20 Jan 2021 13:26:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389790AbhATN0K (ORCPT ); Wed, 20 Jan 2021 08:26:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388268AbhATNSs (ORCPT ); Wed, 20 Jan 2021 08:18:48 -0500 Received: from mail-lf1-x12d.google.com (mail-lf1-x12d.google.com [IPv6:2a00:1450:4864:20::12d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4E7EFC0613C1 for ; Wed, 20 Jan 2021 05:18:07 -0800 (PST) Received: by mail-lf1-x12d.google.com with SMTP id h7so4809886lfc.6 for ; Wed, 20 Jan 2021 05:18:07 -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=KEq8tBsSJotuDC8emCL/6gnLfDlNS7DjovwJhhjL6ms=; b=ULlMSelK9Ah0BMaovUHmsACU3A8+D692YYxmt2OYno3eGXN24zqnixuDonvFpZ2434 yGSCIJLnb9rvtjhVV8XPX2nCR1tR5/W56AKUtGD1OkiGVo7IeB4jiaFQf7E/SPuBZCPk d4Lus8TY9Pvv6JwfYfacYCpF4wqkl22vCHCQTbwiluzAHo44vfyw87aw1bj7GxrJh8cR nZV9kGNYb8OxcaZ9Ql7C/WeH9v4zws6ASGW2+LqT3AtKKoJHzqc0nxsas+X7WZpY7KVr OAUDEHg2PDM3TgJfR2sQZHreqITp3VHs1U9nSDMrPkcdRevPf/w7OuV8CjENhYu9SBn6 VcWw== 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=KEq8tBsSJotuDC8emCL/6gnLfDlNS7DjovwJhhjL6ms=; b=DYWVI6xofib2LHj0akcKQnPTSz9T7bGb/lKtN6f3c8Soendi2fuukf7sfIUqUki25w FgrEgS+ZJzZWUTy1ALnHeuH3RL2kf+BzBrTJy5Nt1BG0u8c4xN11Lj/5xLr7SCQbyI5I pQq3FVfeWWgJqMqJSQmHlgqq5EN8X2xrfR9QcM9fIH2Vmljh9tKUJrBEqeit+viWkJB9 ocjm+SNWleSLveBjiLp2UR1HIWXpGiKVTNA3z74qv3MFY/PXIz3UDanJWoOjQOFUwm0z jQ/3buMAc0R6V9j7Ru5mCcb0CZ/+d2r7DOw+gO8RTCJsVJY1VOxk2V+0JChVjV/j71Dw GdDQ== X-Gm-Message-State: AOAM531PaB1NCQUswb2fQbdWRZmYDBRR3WfqaDJXOVn+iQnSrSCpjV8X ZSIf/G05k29dZ3KluSOEbzleDhSekXHA/36Xlog2Qg== X-Google-Smtp-Source: ABdhPJzqDqJvZXUcfXv4xFpgmlCE0aHWXWLar3aIIwchg7i4ldiK53CzSQfu3T1ZKIGVaiUK6Qge3/wJtkCQkY/hjps= X-Received: by 2002:a19:8cb:: with SMTP id 194mr4180105lfi.463.1611148685415; Wed, 20 Jan 2021 05:18:05 -0800 (PST) MIME-Version: 1.0 References: <20210111170622.2613577-1-surenb@google.com> <20210112074629.GG22493@dhcp22.suse.cz> <20210112174507.GA23780@redhat.com> <20210113142202.GC22493@dhcp22.suse.cz> In-Reply-To: <20210113142202.GC22493@dhcp22.suse.cz> From: Jann Horn Date: Wed, 20 Jan 2021 14:17:39 +0100 Message-ID: Subject: Re: [PATCH v2 1/1] mm/madvise: replace ptrace attach requirement for process_madvise To: Michal Hocko Cc: Suren Baghdasaryan , Oleg Nesterov , Andrew Morton , Kees Cook , Jeffrey Vander Stoep , Minchan Kim , Shakeel Butt , David Rientjes , =?UTF-8?Q?Edgar_Arriaga_Garc=C3=ADa?= , Tim Murray , linux-mm , SElinux list , Linux API , LKML , kernel-team , linux-security-module Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 13, 2021 at 3:22 PM Michal Hocko wrote: > On Tue 12-01-21 09:51:24, Suren Baghdasaryan wrote: > > On Tue, Jan 12, 2021 at 9:45 AM Oleg Nesterov wrote: > > > > > > On 01/12, Michal Hocko wrote: > > > > > > > > On Mon 11-01-21 09:06:22, Suren Baghdasaryan wrote: > > > > > > > > > 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. > > > > > > > > I have to say that ptrace modes are rather obscure to me. So I cannot > > > > really judge whether MODE_READ is sufficient. My understanding has > > > > always been that this is requred to RO access to the address space. But > > > > this operation clearly has a visible side effect. Do we have any actual > > > > documentation for the existing modes? > > > > > > > > I would be really curious to hear from Jann and Oleg (now Cced). > > > > > > Can't comment, sorry. I never understood these security checks and never tried. > > > IIUC only selinux/etc can treat ATTACH/READ differently and I have no idea what > > > is the difference. Yama in particular only does its checks on ATTACH and ignores READ, that's the difference you're probably most likely to encounter on a normal desktop system, since some distros turn Yama on by default. Basically the idea there is that running "gdb -p $pid" or "strace -p $pid" as a normal user will usually fail, but reading /proc/$pid/maps still works; so you can see things like detailed memory usage information and such, but you're not supposed to be able to directly peek into a running SSH client and inject data into the existing SSH connection, or steal the cryptographic keys for the current connection, or something like that. > > I haven't seen a written explanation on ptrace modes but when I > > consulted Jann his explanation was: > > > > PTRACE_MODE_READ means you can inspect metadata about processes with > > the specified domain, across UID boundaries. > > PTRACE_MODE_ATTACH means you can fully impersonate processes with the > > specified domain, across UID boundaries. > > Maybe this would be a good start to document expectations. Some more > practical examples where the difference is visible would be great as > well. Before documenting the behavior, it would be a good idea to figure out what to do with perf_event_open(). That one's weird in that it only requires PTRACE_MODE_READ, but actually allows you to sample stuff like userspace stack and register contents (if perf_event_paranoid is 1 or 2). Maybe for SELinux things (and maybe also for Yama), there should be a level in between that allows fully inspecting the process (for purposes like profiling) but without the ability to corrupt its memory or registers or things like that. Or maybe perf_event_open() should just use the ATTACH mode.