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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59A87EB64DC for ; Wed, 21 Jun 2023 08:52:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231721AbjFUIwa (ORCPT ); Wed, 21 Jun 2023 04:52:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229983AbjFUIw1 (ORCPT ); Wed, 21 Jun 2023 04:52:27 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E58595 for ; Wed, 21 Jun 2023 01:52:26 -0700 (PDT) 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=ZxzonGtfOib4bPz4vU4l7YCxSJ6y+1nTH4FRT1JSooU=; b=dJ1z5ZascKyFFx/kUKDQ2f4eIB NvyeXAQE8zMoi7rFIClyOlPkcXeS/jGBSe5xzH4T8Owk1N0W4N5OFjK6MBDtP8c5Fo1LisZmoJjSt BILykQgxFX9IOOHUNo9A+nGJ5k/m/nuB0kzu2Zfa3US7zPs/UIghVpKWLc48umyhLSrN7LDQqJj07 I6tmHhHKBHzG5p8Cs1miYiYVeXhCM2sNOqzwWJaMiAyH9HZAgb42MwQRUefUz422NXzlFQ5gUvKDW 9ggwBIa1LazU/FrDoXcXqpenU82mYO/SHjBtP5uskORHWCsw/S83R/O5QCbVRwnEMFttkAu7033tb xsXMtJ0A==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qBtZb-00E9kA-35; Wed, 21 Jun 2023 08:52:19 +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 BF69D300137; Wed, 21 Jun 2023 10:52:17 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B020C20825AF7; Wed, 21 Jun 2023 10:52:17 +0200 (CEST) Date: Wed, 21 Jun 2023 10:52:17 +0200 From: Peter Zijlstra To: Kees Cook Cc: x86@kernel.org, alyssa.milburn@linux.intel.com, linux-kernel@vger.kernel.org, samitolvanen@google.com, jpoimboe@kernel.org, joao@overdrivepizza.com, tim.c.chen@linux.intel.com Subject: Re: [PATCH 1/2] x86/cfi: Fix ret_from_fork indirect calls Message-ID: <20230621085217.GI2046280@hirez.programming.kicks-ass.net> References: <20230615193546.949657149@infradead.org> <20230615193722.127844423@infradead.org> <202306201455.AF16F617A@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202306201455.AF16F617A@keescook> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 20, 2023 at 02:56:22PM -0700, Kees Cook wrote: > On Thu, Jun 15, 2023 at 09:35:47PM +0200, Peter Zijlstra wrote: > > The ret_from_fork stub does an indirect call to the kthread function, > > but only knows about Retpolines. Instead of making the asm more > > complicated, punt to C and let the compiler figure it out. > > > > Specifically, this makes it a proper kCFI indirect call when needed (in > > fact, it is nearly impossible to code a kCFI indirect call in asm). > > > > This was the only callsite that was still calling func()+0 on regular > > indirect functions. > > > > Signed-off-by: Peter Zijlstra (Intel) > > I worry this creates a calling gadget, but I don't think it really > counts since it's just converting between two prototypes. Regardless: Ah, since this will never be indirectly called, I should be able to annotate this so it never can be. Let me see what I can get the compiler to do.