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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 60B31C43461 for ; Thu, 17 Sep 2020 15:37:45 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CDC7F22208 for ; Thu, 17 Sep 2020 15:37:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="EqZYq6l0"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="BFLuqVFA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDC7F22208 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=bg0uKl1ahm0mTcwodt8lbKOi9ya9mrWKHP6vf7A1rGY=; b=EqZYq6l0B2oAZ8jD5jukVDWEH ORkgndyCrMt23QI+ZCa85pYqFGXrwaKnvxq15hXKtOBfyZrH/J/cFnMDJf8pNCIkGV3zCG6HkXn/e nTIKChMtIWeHx1rxWclyQl+dAxucKg+0pZ4lTt5j7aNw8C560C7I5EimZEJV8iVe3Q1sxhVnwcPk4 m1nrW9E+eSUyjmbWeVIQITqCXCkITEOMBn6dbxfr2ZUfu02IN3rz2f1kwm/7foeJb0QC9fxNPEZY6 3a0z6SvZx7u3YcEXXp3QZZt+MtGJIRz0I7cMsGGPuPpZdzfTVGO5DuyoogUYvKcfn4CDTYMiWZMHP uvw90LREA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIvxC-00065v-N3; Thu, 17 Sep 2020 15:36:10 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIvxA-00065A-5l for linux-arm-kernel@lists.infradead.org; Thu, 17 Sep 2020 15:36:09 +0000 Received: from [192.168.254.38] (unknown [47.187.206.220]) by linux.microsoft.com (Postfix) with ESMTPSA id B4CB020B7178; Thu, 17 Sep 2020 08:36:03 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com B4CB020B7178 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1600356964; bh=QO+LfG0Faopxheg2cutvYRBT+pPhms6wveYLa1LgL+U=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=BFLuqVFA/BDQQm7DZtjpCvIA39dAw9ux6L9xLBXRs6zIIXnRN+iAbXLuSLqhrzA+k BG7bFfSeOzurlviYcp2xoC7KmQR6uPkch48sGL+8ZSgMbTtNqSk+vcT3F4zKwn48wg Rw5oLxGtZN7S6/Kam+IanR5OdBOQIIId/5GCFEoU= Subject: Re: [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor To: Florian Weimer References: <20200916150826.5990-1-madvenka@linux.microsoft.com> <87v9gdz01h.fsf@mid.deneb.enyo.de> From: "Madhavan T. Venkataraman" Message-ID: <96ea02df-4154-5888-1669-f3beeed60b33@linux.microsoft.com> Date: Thu, 17 Sep 2020 10:36:02 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <87v9gdz01h.fsf@mid.deneb.enyo.de> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200917_113608_377847_C6622C6C X-CRM114-Status: GOOD ( 29.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, oleg@redhat.com, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, libffi-discuss@sourceware.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 9/16/20 8:04 PM, Florian Weimer wrote: > * madvenka: > >> Examples of trampolines >> ======================= >> >> libffi (A Portable Foreign Function Interface Library): >> >> libffi allows a user to define functions with an arbitrary list of >> arguments and return value through a feature called "Closures". >> Closures use trampolines to jump to ABI handlers that handle calling >> conventions and call a target function. libffi is used by a lot >> of different applications. To name a few: >> >> - Python >> - Java >> - Javascript >> - Ruby FFI >> - Lisp >> - Objective C > > libffi does not actually need this. It currently collocates > trampolines and the data they need on the same page, but that's > actually unecessary. It's possible to avoid doing this just by > changing libffi, without any kernel changes. > > I think this has already been done for the iOS port. > The trampoline table that has been implemented for the iOS port (MACH) is based on PC-relative data referencing. That is, the code and data are placed in adjacent pages so that the code can access the data using an address relative to the current PC. This is an ISA feature that is not supported on all architectures. Now, if it is a performance feature, we can include some architectures and exclude others. But this is a security feature. IMO, we cannot exclude any architecture even if it is a legacy one as long as Linux is running on the architecture. So, we need a solution that does not assume any specific ISA feature. >> The code for trampoline X in the trampoline table is: >> >> load &code_table[X], code_reg >> load (code_reg), code_reg >> load &data_table[X], data_reg >> load (data_reg), data_reg >> jump code_reg >> >> The addresses &code_table[X] and &data_table[X] are baked into the >> trampoline code. So, PC-relative data references are not needed. The user >> can modify code_table[X] and data_table[X] dynamically. > > You can put this code into the libffi shared object and map it from > there, just like the rest of the libffi code. To get more > trampolines, you can map the page containing the trampolines multiple > times, each instance preceded by a separate data page with the control > information. > If you put the code in the libffi shared object, how do you pass data to the code at runtime? If the code we are talking about is a function, then there is an ABI defined way to pass data to the function. But if the code we are talking about is some arbitrary code such as a trampoline, there is no ABI defined way to pass data to it except in a couple of platforms such as HP PA-RISC that have support for function descriptors in the ABI itself. As mentioned before, if the ISA supports PC-relative data references (e.g., X86 64-bit platforms support RIP-relative data references) then we can pass data to that code by placing the code and data in adjacent pages. So, you can implement the trampoline table for X64. i386 does not support it. > I think the previous patch submission has also resulted in several > comments along those lines, so I'm not sure why you are reposting > this. IIRC, I have answered all of those comments by mentioning the point that we need to support all architectures without requiring special ISA features. Taking the kernel's help in this is one solution. > >> libffi >> ====== >> >> I have implemented my solution for libffi and provided the changes for >> X86 and ARM, 32-bit and 64-bit. Here is the reference patch: >> >> http://linux.microsoft.com/~madvenka/libffi/libffi.v2.txt > > The URL does not appear to work, I get a 403 error. I apologize for that. That site is supposed to be accessible publicly. I will contact the administrator and get this resolved. Sorry for the annoyance. > >> If the trampfd patchset gets accepted, I will send the libffi changes >> to the maintainers for a review. BTW, I have also successfully executed >> the libffi self tests. > > I have not seen your libffi changes, but I expect that the complexity > is about the same as a userspace-only solution. > > I agree. The complexity is about the same. But the support is for all architectures. Once the common code is in place, the changes for each architecture are trivial. Madhavan > Cc:ing libffi upstream for awareness. The start of the thread is > here: > > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel