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,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable 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 D566FC282DA for ; Tue, 16 Apr 2019 02:19:05 +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 A4EDB2070D for ; Tue, 16 Apr 2019 02:19:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="V/2dbs7g" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A4EDB2070D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.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=HEqu+88rdAxEwaZZ8S67tEHOEDSqfll+CJeCbTjzLJE=; b=V/2dbs7gNo1Pka rTVOp1AgXMNyIl8sni00au12OYRxAjUDS5nqV49zdQAEyyV4Y/MOfUTdMQMbBRTiw2JthzMxuMpaW cPiJB93O7L+ydXcKcybDB5GsTcvsE+LAaOsM/4w46T6WVx8/zl16snXHzhpJBcz0VsBqlz5R9Y/1i 9DpwRq2xuuv9wz+B5aeJiRfsfvqLv+at0vtvX/hFaTk9NwsjGpWudAaZwoXzI6lCEtioHpt1vOw00 gt24xC97xsnfvk8VOAx5NxsUlCY5T642nXXVsUDK0C7iRcn4em+Z6Lr+tONv6HaF6II37UBnHGsld FKPLgATIUNiP6QvsBI3w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hGDgT-0004Eq-Lr; Tue, 16 Apr 2019 02:18:53 +0000 Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hGDgS-0004Ef-Gw; Tue, 16 Apr 2019 02:18:52 +0000 Date: Mon, 15 Apr 2019 19:18:52 -0700 From: Matthew Wilcox To: Herbert Xu Subject: Re: [PATCH] crypto: testmgr - allocate buffers with __GFP_COMP Message-ID: <20190416021852.GA18616@bombadil.infradead.org> References: <20190411192607.GD225654@gmail.com> <20190411192827.72551-1-ebiggers@kernel.org> <20190415022412.GA29714@bombadil.infradead.org> <20190415024615.f765e7oagw26ezam@gondor.apana.org.au> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190415024615.f765e7oagw26ezam@gondor.apana.org.au> User-Agent: Mutt/1.9.2 (2017-12-15) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux ARM , Kees Cook , Rik van Riel , Linux Kernel Mailing List , Eric Biggers , linux-mm@kvack.org, linux-security-module , Geert Uytterhoeven , linux-crypto , Laura Abbott , Dmitry Vyukov 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 On Mon, Apr 15, 2019 at 10:46:15AM +0800, Herbert Xu wrote: > On Sun, Apr 14, 2019 at 07:24:12PM -0700, Matthew Wilcox wrote: > > On Thu, Apr 11, 2019 at 01:32:32PM -0700, Kees Cook wrote: > > > > @@ -156,7 +156,8 @@ static int __testmgr_alloc_buf(char *buf[XBUFSIZE], int order) > > > > int i; > > > > > > > > for (i = 0; i < XBUFSIZE; i++) { > > > > - buf[i] = (char *)__get_free_pages(GFP_KERNEL, order); > > > > + buf[i] = (char *)__get_free_pages(GFP_KERNEL | __GFP_COMP, > > > > + order); > > > > > > Is there a reason __GFP_COMP isn't automatically included in all page > > > allocations? (Or rather, it seems like the exception is when things > > > should NOT be considered part of the same allocation, so something > > > like __GFP_SINGLE should exist?.) > > > > The question is not whether or not things should be considered part of the > > same allocation. The question is whether the allocation is of a compound > > page or of N consecutive pages. Now you're asking what the difference is, > > and it's whether you need to be able to be able to call compound_head(), > > compound_order(), PageTail() or use a compound_dtor. If you don't, then > > you can save some time at allocation & free by not specifying __GFP_COMP. > > Thanks for clarifying Matthew. > > Eric, this means that we should not use __GFP_COMP here just to > silent what is clearly a broken warning. I agree; if the crypto code is never going to try to go from the address of a byte in the allocation back to the head page, then there's no need to specify GFP_COMP. But that leaves us in the awkward situation where HARDENED_USERCOPY_PAGESPAN does need to be able to figure out whether 'ptr + n - 1' lies within the same allocation as ptr. Without using a compound page, there's no indication in the VM structures that these two pages were allocated as part of the same allocation. We could force all multi-page allocations to be compound pages if HARDENED_USERCOPY_PAGESPAN is enabled, but I worry that could break something. We could make it catch fewer problems by succeeding if the page is not compound. I don't know, these all seem like bad choices to me. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel