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=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 541ADC5CFFE for ; Tue, 11 Dec 2018 17:21:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2091D20851 for ; Tue, 11 Dec 2018 17:21:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2091D20851 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 S1727375AbeLKRV4 (ORCPT ); Tue, 11 Dec 2018 12:21:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35543 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726231AbeLKRV4 (ORCPT ); Tue, 11 Dec 2018 12:21:56 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 02B4A811DC; Tue, 11 Dec 2018 17:21:55 +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 CE9705D73F; Tue, 11 Dec 2018 17:21:53 +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: Tue, 11 Dec 2018 12:21:52 -0500 In-Reply-To: (Jeff Moyer's message of "Thu, 06 Dec 2018 17:26:33 -0500") 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 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 11 Dec 2018 17:21:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeff Moyer writes: > Jeff Moyer writes: > >> 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? > > Too quick on the draw. Here's a patch that compiles. ;-) Hi, Matthew, I'm going to submit this version formally. If you're interested in converting the ioctx_table to xarray, you can do that separately from a security fix. I would include a performance analysis with that patch, though. The idea of using a radix tree for the ioctx table was discarded due to performance reasons--see commit db446a08c23d5 ("aio: convert the ioctx list to table lookup v3"). I suspect using the xarray will perform similarly. Cheers, Jeff > diff --git a/fs/aio.c b/fs/aio.c > index 97f983592925..aac9659381d2 100644 > --- a/fs/aio.c > +++ b/fs/aio.c > @@ -45,6 +45,7 @@ > > #include > #include > +#include > > #include "internal.h" > > @@ -1038,6 +1039,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) > if (!table || id >= table->nr) > goto out; > > + id = array_index_nospec(id, table->nr); > ctx = rcu_dereference(table->table[id]); > if (ctx && ctx->user_id == ctx_id) { > if (percpu_ref_tryget_live(&ctx->users)) > > -- > To unsubscribe, send a message with 'unsubscribe linux-aio' in > the body to majordomo@kvack.org. For more info on Linux AIO, > see: http://www.kvack.org/aio/ > Don't email: aart@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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> Date: Tue, 11 Dec 2018 12:21:52 -0500 In-Reply-To: (Jeff Moyer's message of "Thu, 06 Dec 2018 17:26:33 -0500") Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: Jeff Moyer writes: > Jeff Moyer writes: > >> 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? > > Too quick on the draw. Here's a patch that compiles. ;-) Hi, Matthew, I'm going to submit this version formally. If you're interested in converting the ioctx_table to xarray, you can do that separately from a security fix. I would include a performance analysis with that patch, though. The idea of using a radix tree for the ioctx table was discarded due to performance reasons--see commit db446a08c23d5 ("aio: convert the ioctx list to table lookup v3"). I suspect using the xarray will perform similarly. Cheers, Jeff > diff --git a/fs/aio.c b/fs/aio.c > index 97f983592925..aac9659381d2 100644 > --- a/fs/aio.c > +++ b/fs/aio.c > @@ -45,6 +45,7 @@ > > #include > #include > +#include > > #include "internal.h" > > @@ -1038,6 +1039,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) > if (!table || id >= table->nr) > goto out; > > + id = array_index_nospec(id, table->nr); > ctx = rcu_dereference(table->table[id]); > if (ctx && ctx->user_id == ctx_id) { > if (percpu_ref_tryget_live(&ctx->users)) > > -- > To unsubscribe, send a message with 'unsubscribe linux-aio' in > the body to majordomo@kvack.org. For more info on Linux AIO, > see: http://www.kvack.org/aio/ > Don't email: aart@kvack.org