From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="LwFyl/Nj" Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06787FE; Sun, 10 Dec 2023 03:45:24 -0800 (PST) Received: by mail-ej1-x631.google.com with SMTP id a640c23a62f3a-a1c7b20f895so414676866b.2; Sun, 10 Dec 2023 03:45:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702208721; x=1702813521; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=Yp3hxbGdS2eZBPtlqCepXeiPKyyCDAaMr2U9ZBJTXkg=; b=LwFyl/Njv6bsLT2DAMPOZBwxWFtYrQuTwHaEH9Ok+WrVX2s14Quq10g9mEUg7zEHm9 ZUNOhzP/ce1sWjTCot9hG/wsgMGtZxro5tA4kPQtvRS28tmM5qQRO7ydvl6QslWHVkP7 bjVOVDipxeFDy45RdsUNg4PdoY+0Vo/zi+hOhw7jLNefj+YwhOi4h+DKPTy/wVBlOcc+ pcvzIlqk6HwmvL3ieM1GAW2vhnvvAFV0GLG/giwMmMTssOs3Sma8n8qihzOWbOhgOLTO fFiW1cTDt33X7KWwSsb0lXrKPq/qXXwNpV8Tw/O9BoHttBBh04OTg14Z6ZM/+15WYpn9 1gUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702208721; x=1702813521; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Yp3hxbGdS2eZBPtlqCepXeiPKyyCDAaMr2U9ZBJTXkg=; b=d8cndg5peX2HV4eXltkrVB5w4XHxwiUpKLt8zVhDIeXsX0+JOfvcuTfTT+KHadOpj2 ZtpR4oqcbNgDpYwPvWYGK0IsL2tJ3PmXC8H36znMe/x8FsnyL5XOunxWE37DuxatQbJ5 YvA6mGoefVykVFzjenZC65XG1NMN2SN44LyqetQQ8O49PsqT9jVQ4y1kU7djOL0tksVH 2Sna/4KsEhnCED+tZwGhgYqTfJrTgnQ5gPa/Olps1EmA17gbQHs7VAA35rGu1au0OlM3 fSbg6vcKiWV8Nk2GEwJRsLKwi9d29Wjxg6/5rPkd5xIHUeARAswGPjI241tpGte4jUh/ KRxg== X-Gm-Message-State: AOJu0YySlJFaayvI6Fvgz3TWyZicu5/nWKZAjn8YaoPJitEEo9qBGsYe A5DxFA/TFWfjDZlgkyv+9w== X-Google-Smtp-Source: AGHT+IEqCsZ7ZXLuWOmv3maORdUwlfQjqZozZP+afPI3r5sYdATksOhbu8geeOgTbY1EoEt+o4ZFWg== X-Received: by 2002:a17:906:512:b0:a19:a1ba:8cb6 with SMTP id j18-20020a170906051200b00a19a1ba8cb6mr1279246eja.84.1702208721021; Sun, 10 Dec 2023 03:45:21 -0800 (PST) Received: from p183 ([46.53.250.155]) by smtp.gmail.com with ESMTPSA id fj8-20020a1709069c8800b00a1d5c342674sm3295540ejc.27.2023.12.10.03.45.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 Dec 2023 03:45:20 -0800 (PST) Date: Sun, 10 Dec 2023 14:45:18 +0300 From: Alexey Dobriyan To: "Eric W. Biederman" Cc: Kees Cook , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Randy Dunlap , Bagas Sanjaya , Jonathan Corbet , linux-mm@kvack.org Subject: Re: [PATCH v3] ELF: document some de-facto PT_* ABI quirks Message-ID: <57f5aa9d-79c5-4f65-b90f-204600edfb80@p183> References: <2acb586c-08a9-42d9-a41e-7986cc1383ea@p183> <87edp7jyu4.fsf@meer.lwn.net> <88d3f1bb-f4e0-4c40-9304-3843513a1262@p183> <202312061456.2103DA1@keescook> <874jgugilq.fsf@email.froward.int.ebiederm.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <874jgugilq.fsf@email.froward.int.ebiederm.org> On Thu, Dec 07, 2023 at 09:03:45AM -0600, Eric W. Biederman wrote: > Kees Cook writes: > > > *thread necromancy* Question below... > > > > On Sat, Apr 15, 2023 at 08:37:29PM +0300, Alexey Dobriyan wrote: > >> Turns out rules about PT_INTERP, PT_GNU_STACK and PT_GNU_PROPERTY > >> program headers are slightly different. > >> > >> Signed-off-by: Alexey Dobriyan > >> --- > >> > >> v3: move to Documentation/userspace-api/ > >> v2: integrate into documentation build system > >> > >> Documentation/userspace-api/ELF.rst | 34 ++++++++++++++++++++++++++++++++++ > >> Documentation/userspace-api/index.rst | 1 + > >> 2 files changed, 35 insertions(+) > >> > >> new file mode 100644 > >> --- /dev/null > >> +++ b/Documentation/userspace-api/ELF.rst > >> @@ -0,0 +1,34 @@ > >> +.. SPDX-License-Identifier: GPL-2.0 > >> + > >> +================================= > >> +Linux-specific ELF idiosyncrasies > >> +================================= > >> + > >> +Definitions > >> +=========== > >> + > >> +"First" program header is the one with the smallest offset in the file: > >> +e_phoff. > > Confusing e_phoff is the defined location of the array of program > headers. > > Perhaps the "First" in that array with the lowest e_phnum? > > >> +"Last" program header is the one with the biggest offset in the file: > >> +e_phoff + (e_phnum - 1) * sizeof(Elf_Phdr). > > Ditto the "Last" in the array with the largest array index. > > I nit pick this because it sounded at first like you were talking about > p_offset. Which is a value contained in the program header entry. > > >> +PT_INTERP > >> +========= > >> + > >> +First PT_INTERP program header is used to locate the filename of ELF > >> +interpreter. Other PT_INTERP headers are ignored (since Linux 2.4.11). > >> + > >> +PT_GNU_STACK > >> +============ > >> + > >> +Last PT_GNU_STACK program header defines userspace stack executability > >> +(since Linux 2.6.6). Other PT_GNU_STACK headers are ignored. > >> + > >> +PT_GNU_PROPERTY > >> +=============== > >> + > >> +ELF interpreter's last PT_GNU_PROPERTY program header is used (since > >> +Linux 5.8). If interpreter doesn't have one, then the last PT_GNU_PROPERTY > >> +program header of an executable is used. Other PT_GNU_PROPERTY headers > >> +are ignored. > > A more interesting property to document is that PT_GNU_PROPERTY must > precede PT_INTERP in the linux implementation, otherwise we ignore it. > > > Should we perhaps solve some of these in some way? What would folks > > prefer the behaviors be? (I like to have things been "as expected", but > > it's not very obvious here for redundant headers...) > > All of these are really headers that should appear only once. Yes. > Quite frankly if we are going to do something with this my sense is that > we should fail the execve with a clear error code as userspace should > not be doing this, and accepting a malformed executable will hide > errors, and perhaps hide someone causing problems. Maybe do it for PT_GNU_PROPERTY which is relatively new. > I really don't think having multiple copies of these headers with > different values is something we should encourage. > > It looks like -ELIBBAD is the documented way to fail and report > a bad file format. It is obvious you don't know how much will break. > For PT_GNU_PROPTERTY perhaps we should accept it anywhere, instead of > silently ignoring it depending upon it's location? > > I thinking change the code to talk one pass through the program headers > to identify the interesting headers, and then with the interesting > headers all identified we go do something with them. > > Anyway just my opinion, but that is what it feels like to me. _Not_ checking for duplicates will result in the simplest and fastest exec. which is what current code does.