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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 06EB9C3A5A9 for ; Mon, 4 May 2020 16:52:47 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C3DF32073E for ; Mon, 4 May 2020 16:52:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="uxkusMIb"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="uyMa7may" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3DF32073E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.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:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Embe2UKPiqpyaLhE25/rrP9m0jdoBF76TORDbotHbuo=; b=uxkusMIb3uSt6w MPmi33NzpiJm6VJ6CE3Q/yLbVYEGC6D4Ar+ak6BbQminR6UIyrDMU9jZpAKpNQmscAveb7gWPoJt0 exWLrsSIQw4Yh2NHRjMojJrHYId9X30SOahbaBXHZs1Rup2KmdL1Bj1c3op7xaOCSahHWu2mo/mFn ac0zZs/DCKIbFl6oyttvWvorNW6nsFSqNQwYNXDnVVt40Y1cZg2GGSsXKtXVI8obp4wYhv2ozOGbJ 3cECM39OeFJ1bshazKOzhoQXh9NgEkquLD1MbdOjxBnOTC7weK7+wnd9yQeMObW5wPZZFYbh4pOnQ avX4AKg6m3M/PFWTe/5w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVeKj-0006Mo-ON; Mon, 04 May 2020 16:52:45 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVeKb-0006L2-1W for linux-arm-kernel@lists.infradead.org; Mon, 04 May 2020 16:52:43 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C292E20721; Mon, 4 May 2020 16:52:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588611155; bh=pHevdodwKI9AchWwf20bTvyMZmY/KXT51VAk5UHfloY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uyMa7mayYmQKcwMDm+GOx012e1zqDeyv+W5L6bDtfpKFAZ+E7dHLgSdsy/T09kHTW ixd15enHaJKKfVWzOVcZQBM4JTXKH1eXGREFx5btkK873B8qrSEX32IqtAqg24KSMC y7A6s2xNnFeJRxYbjVN/DbsKn+VXK3WbXoGH2kNQ= Date: Mon, 4 May 2020 17:52:28 +0100 From: Will Deacon To: Sami Tolvanen Subject: Re: [PATCH v11 01/12] add support for Clang's Shadow Call Stack (SCS) Message-ID: <20200504165227.GB1833@willie-the-truck> References: <20191018161033.261971-1-samitolvanen@google.com> <20200416161245.148813-1-samitolvanen@google.com> <20200416161245.148813-2-samitolvanen@google.com> <20200420171727.GB24386@willie-the-truck> <20200420211830.GA5081@google.com> <20200422173938.GA3069@willie-the-truck> <20200422235134.GA211149@google.com> <202004231121.A13FDA100@keescook> <20200424112113.GC21141@willie-the-truck> <20200427204546.GA80713@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200427204546.GA80713@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200504_095237_122865_98ED5AEF X-CRM114-Status: GOOD ( 26.24 ) 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: Mark Rutland , Juri Lelli , kernel-hardening@lists.openwall.com, Peter Zijlstra , Catalin Marinas , Marc Zyngier , Masahiro Yamada , clang-built-linux@googlegroups.com, Ingo Molnar , Laura Abbott , Dave Martin , Kees Cook , Jann Horn , Steven Rostedt , linux-arm-kernel@lists.infradead.org, Michal Marek , Ard Biesheuvel , Nick Desaulniers , linux-kernel@vger.kernel.org, Miguel Ojeda , James Morse , Masami Hiramatsu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Archived-At: List-Archive: On Mon, Apr 27, 2020 at 01:45:46PM -0700, Sami Tolvanen wrote: > On Fri, Apr 24, 2020 at 12:21:14PM +0100, Will Deacon wrote: > > Also, since you mentioned the lack of redzoning, isn't it a bit dodgy > > allocating blindly out of the kmem_cache? It means we don't have a redzone > > or a guard page, so if you can trigger something like a recursion bug then > > could you scribble past the SCS before the main stack overflows? Would this > > clobber somebody else's SCS? > > I agree that allocating from a kmem_cache isn't ideal for safety. It's a > compromise to reduce memory overhead. Do you think it would be a problem if we always allocated a page for the SCS? > > The vmap version that I asked Sami to drop > > is at least better in this regard, although the guard page is at the wrong > > end of the stack and we just hope that the allocation below us didn't pass > > VM_NO_GUARD. Looks like the same story for vmap stack :/ > > SCS grows up and the guard page is after the allocation, so how is it at > the wrong end? Am I missing something here? Sorry, I'd got the SCS upside-down in my head (hey, that second 'S' stands for 'Stack'!). But I think I'm right about vmap stack, which feels a little fragile even though it seems to work out today with the very limited uses of VM_NO_GUARD. > > If we split the pointer in two (base, offset) then we could leave the > > base live in the thread_info, not require alignment of the stacks (which > > may allow for unconditional redzoning?) and then just update the offset > > value on context switch, which could be trivially checked as part of the > > existing stack overflow checking on kernel entry. > > I sent out v13 with split pointers, but I'm not sure it's convenient to > add an overflow check to kernel_ventry where the VMAP_STACK check is > done. I suppose I could add a check to kernel_entry after we load x18 > from tsk. Thoughts? I'll take a look at v13, since at this stage I'm keen to get something queued up so that we can use it as a base for further improvements without you having to repost the whole stack every time. Cheers, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel