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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id CBAB2C433FE for ; Tue, 17 May 2022 09:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=X4HABQiOEoeIqb1m0og+s/t7QFOHx5GMSpmosay1x+c=; b=jnDIuZGgaMrPoU Dg1vYDzO23lT9h9YHkaLE8Ew+icqEc64LRaZQ3z+PLRIft/RHBzM3yuiyG4ha5ffdTNL1RU+CsIIR cs6oaUKcyXSfNj6c1WzTu6yDPsirsuUDSB4TaAxljyfcybhYtGmT57iWKfwwGRy96JwezZTNP2Z4x xjm/rw2Jv6Ua5wNl5gwMxusfzIJ6lkQexIGa6RINfp/FuZT2Iug1dphkZsYeKgmzUzJDosdUAA8ZI TB+jO05ELq1n4V0KymIzgjlv6nHMj7lP0phUBxrrC7o3RBrtqBZDrI9tA/fLlpva1zt3xcq+HbPiU M1u3ML9f8COroGa+9Ymg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nqtfD-00CndD-Dd; Tue, 17 May 2022 09:38:47 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nqtfA-00CnbI-5x for linux-arm-kernel@bombadil.infradead.org; Tue, 17 May 2022 09:38:44 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=jwTi2Cazog8blP0yOGLXWlJcsxSDGZ2u4uY9kxsLkfk=; b=MTdKy2r7vz9qnE0wpTp07nMDEg ljCp1Zb2NriOnwiA/uzXXdtuSEEAt+8MmHDW386odcrFLXR7ho+3sO3bDv22akTTPVfMMBXnv+sYI g6gwbLw7UoFN9kxB7jC1PnSyV0mnJYnpYuoffSyjX5HIclZnpntQBYF3T/PccfzfZB5YTQq8536iO PNACVypbg/9epOBrixidP1XzJqc62oEdrDBFOtkey9RO2PV2y4tUg/sKetgnmz/oaloCU6sVTc76I GIFxs0GQBFaxTwXsfnWWxc12azbRX8zbFTrsQm1XHYjiH/MDS52S3YLfghOmjbjQalbuvQq7Rp/3m 60MDw/MA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nqtf5-00Aje0-Dt; Tue, 17 May 2022 09:38:39 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7F7A130031C; Tue, 17 May 2022 11:38:36 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 66A62202BC439; Tue, 17 May 2022 11:38:36 +0200 (CEST) Date: Tue, 17 May 2022 11:38:36 +0200 From: Peter Zijlstra To: David Laight Cc: Kees Cook , Sami Tolvanen , "linux-kernel@vger.kernel.org" , Josh Poimboeuf , "x86@kernel.org" , Catalin Marinas , Will Deacon , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Joao Moreira , Sedat Dilek , Steven Rostedt , "linux-hardening@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "llvm@lists.linux.dev" Subject: Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG Message-ID: References: <20220513202159.1550547-1-samitolvanen@google.com> <20220513202159.1550547-21-samitolvanen@google.com> <20220516183047.GM76023@worktop.programming.kicks-ass.net> <202205161531.3339CA95@keescook> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Tue, May 17, 2022 at 08:48:41AM +0000, David Laight wrote: > From: Peter Zijlstra > > Sent: 17 May 2022 09:41 > ... > > > If we use %eax instead of %r10d for the hash transfer (as per Joao), and > > > use int3 instead of ud2, then we can shrink the fineibt sequence to: > > > > > > __cfi_\func: > > > endbr # 4 > > > xorl $0x12345678, %eax # 5 > > > jz 1f # 2 > > > int3 # 1 > > > \func: > > > ... > > > > > > Which is 12 bytes, and needs a larger preamble (up from 9 in the current > > > proposal). > > > > On all that; perhaps it would be good to have a compiler option to > > specify the preamble size. It can enforce the minimum at 7 to have at > > least the required: > > > > movl $0x12345678, %eax > > int3 > > int3 > > > > but any larger number will just increase the preamble with int3 padding > > at the top. > > > > That can go right along with the option to supress endbr when preamble > > :-) > > You also need a compiler option to specify the register. > While (I think) %eax is usable in kernel, it isn't in userspace. > It is used in varargs calls to pass (IIRC) the number of fp > args that are passed in registers. You're mistaken, the compiler doesn't emit the FineIBT code *at*all*. That's all patched in later. For kCFI the mov is never executed and is only there to make it a valid instruction. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel