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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 645C3C433DF for ; Thu, 21 May 2020 23:30:46 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B6425207F9 for ; Thu, 21 May 2020 23:30:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="MpBbNEwc" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6425207F9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18854-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 5624 invoked by uid 550); 21 May 2020 23:30:39 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 5599 invoked from network); 21 May 2020 23:30:38 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=1gibyxiWx0QNF1j9zPlChAHDNDwaEmxS/M++y57RUrs=; b=MpBbNEwcm5wRraAV5OiblA2zPdqD9KNWPoAHUgqKM8Rbst+M/JjT04I9uUUH1EALHs lW+yRfivRRJqil+IgM0QapLJey39Kg/2mP1L3qwPliX5LQPUjzvp6TxCDx0umxNp19gB nFFRmUzPGKWjr17uv2KuvHYtLQgkR9/n6ZRqg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=1gibyxiWx0QNF1j9zPlChAHDNDwaEmxS/M++y57RUrs=; b=LxV35jVV8ljG2yJZBrwtSIx2nSNiBrEFELNMz2ibpJZoIN/oDCs9PThaTyVDzS0vWj nu5xsVUTajuqN7rEELH/Pd/c6xbpkEWkijucJM7SByas3iGaDPIjLNA4uanijh30Zayd Yyjd4K9gSyDlO5JUGtXQ5n9g0CjkTcO0VCRHkQkih6+vh6IsxrjQM08ppUHF/+NSb5dW B7bZJ2EEYqj6U+dw0jGNwpLTadzbObIvUubfTEZVZIEsftuPGZHntLwaClvXtAiEP6cU kXMXEFqMl+er5Ghc/tb5VttyhlJiMqJRAFh7ODYJT4fhCT41A0JDP0ezhT7ejTL7vJ74 Qutw== X-Gm-Message-State: AOAM5323wfXOnESksl7MdKXkA7QvaZTJBV/haauA0hht1zFpQ1wO8bkV +epNLv8vgVtxsE4fbjH4ArrJ9g== X-Google-Smtp-Source: ABdhPJy9tCvODJaSjshfgmC7fdO80oHfJyQWMgbloCJ5mYHG3BMqD79HqFicR3fubN7UfR62DwQKIw== X-Received: by 2002:a63:546:: with SMTP id 67mr11688886pgf.364.1590103825857; Thu, 21 May 2020 16:30:25 -0700 (PDT) Date: Thu, 21 May 2020 16:30:23 -0700 From: Kees Cook To: Thomas Gleixner Cc: Kristen Carlson Accardi , mingo@redhat.com, bp@alien8.de, arjan@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, rick.p.edgecombe@intel.com Subject: Re: [PATCH v2 0/9] Function Granular KASLR Message-ID: <202005211604.86AE1C2@keescook> References: <20200521165641.15940-1-kristen@linux.intel.com> <87367sudpl.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87367sudpl.fsf@nanos.tec.linutronix.de> On Fri, May 22, 2020 at 12:26:30AM +0200, Thomas Gleixner wrote: > I understand how this is supposed to work, but I fail to find an > explanation how all of this is preserving the text subsections we have, > i.e. .kprobes.text, .entry.text ...? I had the same question when I first started looking at earlier versions of this series! :) > I assume that the functions in these subsections are reshuffled within > their own randomized address space so that __xxx_text_start and > __xxx_text_end markers still make sense, right? No, but perhaps in the future. Right now, they are entirely ignored and left untouched. The current series only looks at the sections produced by -ffunction-sections, which is to say only things named ".text.$thing" (e.g. ".text.func1", ".text.func2"). Since the "special" text sections in the kernel are named ".$thing.text" (specifically to avoid other long-standing linker logic that does similar .text.* pattern matches) they get ignored by FGKASLR right now too. Even more specifically, they're ignored because all of these special _input_ sections are actually manually collected by the linker script into the ".text" _output_ section, which FGKASLR ignores -- it can only randomize the final output sections (and has no basic block visibility into the section contents), so everything in .text is untouched. Because these special sections are collapsed into the single .text output section is why we've needed the __$thing_start and __$thing_end symbols manually constructed by the linker scripts: we lose input section location/size details once the linker collects them into an output section. > I'm surely too tired to figure it out from the patches, but you really > want to explain that very detailed for mere mortals who are not deep > into this magic as you are. Yeah, it's worth calling out, especially since it's an area of future work -- I think if we can move the special sections out of .text into their own output sections that can get randomized and we'll have section position/size information available without the manual ..._start/_end symbols. But this will require work with the compiler and linker to get what's needed relative to -ffunction-sections, teach the kernel about the new way of getting _start/_end, etc etc. So, before any of that, just .text.* is a good first step, and after that I think next would be getting .text randomized relative to the other .text.* sections (IIUC, it is entirely untouched currently, so only the standard KASLR base offset moves it around). Only after that do we start poking around trying to munge the special section contents (which requires use solving a few problems simultaneously). :) -- Kees Cook