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=-13.2 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 014A4C43381 for ; Tue, 2 Feb 2021 05:35:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA2C364EE7 for ; Tue, 2 Feb 2021 05:35:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231725AbhBBFfY (ORCPT ); Tue, 2 Feb 2021 00:35:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231538AbhBBFfH (ORCPT ); Tue, 2 Feb 2021 00:35:07 -0500 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 75C13C061573 for ; Mon, 1 Feb 2021 21:34:25 -0800 (PST) Received: by mail-wm1-x32d.google.com with SMTP id j11so412990wmi.3 for ; Mon, 01 Feb 2021 21:34:25 -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=lD+9VdFDDbbGKdh4Zlx/S6kSI7nJIlJMTXOt77nYf50=; b=c6ADmGsDwHXz5pqsJbysFZOPf2sccXandZLMCxhV2SBY5AeEWS9MvAu3A1L3a1CjhL NPCrbMA6t0stZ0Eq6KILOn6lTLJd6/Wparn+DKG1OEOl7DvoDnjdCBw3yGA2b/DkOxFj bDCLUPdLOGT6qFlvKp4N/U8LR5N9kYRS8GlSn6HOoZsKSUBhyH3zg3zWYV6D2hSPkANy sGFrnNBfW/cxZ9vseIaZXp2D8HnVZrLnqj9nGpSdeiw60EG1qr/XVwEcZgcoBSScv83v r+F1d0el8pKgYroBTfOLfgDhOG7Hcutr8ToP92EmfFiSVg75RMkO4dr7oUpoGRoS3wRX HTdg== 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=lD+9VdFDDbbGKdh4Zlx/S6kSI7nJIlJMTXOt77nYf50=; b=Du+S3DuoGKEwRAryl34EjfVrNHhDpsXe/FkmNI9E/1UoupAJ57bBSb5W9KfkAYmBJD /XL1wKRnrX3FBvrzC3BllTMtREC+rY9BtbTVKp2G6ph/Q6AInZQnei6Qc1sLtS+3YQdk XrfJFxgcVErT24qN/sz4TVN7oQZZ9SynU1pN4LHofgZazkY5WeDotFDaOxit1trIR6QY qS6R+xGQWZrdfniBBhWpiouI2rpGfCbweluoUKu4Nu2NpaP15Z1pp26eCq8yTWwYPudG Sl+ZJbSUUqOa+yso8/+EhT02HyUAZAkgcw5doZt5g0IYyn3qy3S0z/V0wE6knYnEOmoK X7Jw== X-Gm-Message-State: AOAM53232lNFyItFBxAjNh3zFQRVNmfNlIWtFRivrswg2hWU1bxbRZls R/nu71x7wfRUxJkFeY5pXn/scQsmn2feS6PL+iAPpQ== X-Google-Smtp-Source: ABdhPJz6ttAxWJJKNXWH8Zat2eIPwUyJ+Sf7ECY2vlX2Nz9RgCcMqIkMT272RDNbBCLgqaqpUVLQC9YR8N97KTCll7k= X-Received: by 2002:a1c:acc9:: with SMTP id v192mr1888469wme.22.1612244064008; Mon, 01 Feb 2021 21:34:24 -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> <20210126135254.GP827@dhcp22.suse.cz> In-Reply-To: From: Suren Baghdasaryan Date: Mon, 1 Feb 2021 21:34:12 -0800 Message-ID: Subject: Re: [PATCH v2 1/1] mm/madvise: replace ptrace attach requirement for process_madvise To: Michal Hocko Cc: Jann Horn , 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 , stable Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 28, 2021 at 11:08 PM Suren Baghdasaryan wrote: > > On Thu, Jan 28, 2021 at 11:51 AM Suren Baghdasaryan wrote: > > > > On Tue, Jan 26, 2021 at 5:52 AM 'Michal Hocko' via kernel-team > > wrote: > > > > > > On Wed 20-01-21 14:17:39, Jann Horn wrote: > > > > 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. > > > > > > Thanks for the clarification. I still cannot say I would have a good > > > mental picture. Having something in Documentation/core-api/ sounds > > > really needed. Wrt to perf_event_open it sounds really odd it can do > > > more than other places restrict indeed. Something for the respective > > > maintainer but I strongly suspect people simply copy the pattern from > > > other places because the expected semantic is not really clear. > > > > > > > Sorry, back to the matters of this patch. Are there any actionable > > items for me to take care of before it can be accepted? The only > > request from Andrew to write a man page is being worked on at > > https://lore.kernel.org/linux-mm/20210120202337.1481402-1-surenb@google.com/ > > and I'll follow up with the next version. I also CC'ed stable@ for > > this to be included into 5.10 per Andrew's request. That CC was lost > > at some point, so CC'ing again. > > > > I do not see anything else on this patch to fix. Please chime in if > > there are any more concerns, otherwise I would ask Andrew to take it > > into mm-tree and stable@ to apply it to 5.10. > > Thanks! > > process_madvise man page V2 is posted at: > https://lore.kernel.org/linux-mm/20210129070340.566340-1-surenb@google.com/ process_madvise man page V3 is posted at: https://lore.kernel.org/linux-mm/20210202053046.1653012-1-surenb@google.com/ > > > > > > > > -- > > > Michal Hocko > > > SUSE Labs > > > > > > -- > > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. > > >