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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 9DB7CC04EB8 for ; Thu, 6 Dec 2018 22:21:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6A4F220868 for ; Thu, 6 Dec 2018 22:21:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A4F220868 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726098AbeLFWVe (ORCPT ); Thu, 6 Dec 2018 17:21:34 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40332 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725939AbeLFWVd (ORCPT ); Thu, 6 Dec 2018 17:21:33 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 698B6ED263; Thu, 6 Dec 2018 22:21:33 +0000 (UTC) Received: from segfault.boston.devel.redhat.com (segfault.boston.devel.redhat.com [10.19.60.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 34B025D9CB; Thu, 6 Dec 2018 22:21:32 +0000 (UTC) From: Jeff Moyer To: Matthew Wilcox Cc: Alexander Viro , Benjamin LaHaise , Andrew Morton , Kees Cook , linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Carpenter Subject: Re: [PATCH] aio: Convert ioctx_table to XArray References: <20181128183531.5139-1-willy@infradead.org> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 Date: Thu, 06 Dec 2018 17:21:31 -0500 In-Reply-To: <20181128183531.5139-1-willy@infradead.org> (Matthew Wilcox's message of "Wed, 28 Nov 2018 10:35:31 -0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 06 Dec 2018 22:21:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Matthew Wilcox writes: > This custom resizing array was vulnerable to a Spectre attack (speculating > off the end of an array to a user-controlled offset). The XArray is > not vulnerable to Spectre as it always masks its lookups to be within > the bounds of the array. I'm not a big fan of completely re-writing the code to fix this. Isn't the below patch sufficient? -Jeff diff --git a/fs/aio.c b/fs/aio.c index 97f983592925..9402ae0b63d5 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1038,6 +1038,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) if (!table || id >= table->nr) goto out; + id = array_index_nospec(index, table->nr); ctx = rcu_dereference(table->table[id]); if (ctx && ctx->user_id == ctx_id) { if (percpu_ref_tryget_live(&ctx->users))