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=-13.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 68A4FC388F7 for ; Thu, 22 Oct 2020 12:42:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C10622267 for ; Thu, 22 Oct 2020 12:42:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LEbVq+Zr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2505387AbgJVMmk (ORCPT ); Thu, 22 Oct 2020 08:42:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:20755 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2505408AbgJVMmk (ORCPT ); Thu, 22 Oct 2020 08:42:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603370558; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=D8NfRDK57IWkyMuy8F79W605svkUQv4zH8HJOm5hlKE=; b=LEbVq+ZrJke0vg13llK+BZqC/21rsoTGDFUIHWT46+6ySArRdcDRbUXXXumnwxYUL+pUNZ zRL+HSSLigXyqpbqe1YKAzgf9HLAZOmaMKoeNM/Ot83vDL8JMgridaAskzEW8//dGytvKY p2HZswBjeWhgB6psIAc4Gm4CHDTZK8E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-137-JAg57F3NO6i2Qkw59bI5bQ-1; Thu, 22 Oct 2020 08:42:34 -0400 X-MC-Unique: JAg57F3NO6i2Qkw59bI5bQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 90D1C81C9AF; Thu, 22 Oct 2020 12:42:30 +0000 (UTC) Received: from [10.36.113.152] (ovpn-113-152.ams2.redhat.com [10.36.113.152]) by smtp.corp.redhat.com (Postfix) with ESMTP id 05FBF6EF62; Thu, 22 Oct 2020 12:42:24 +0000 (UTC) Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" To: Greg KH Cc: David Laight , Al Viro , Nick Desaulniers , Christoph Hellwig , "kernel-team@android.com" , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" References: <20201022082654.GA1477657@kroah.com> <80a2e5fa-718a-8433-1ab0-dd5b3e3b5416@redhat.com> <5d2ecb24db1e415b8ff88261435386ec@AcuMS.aculab.com> <20201022090155.GA1483166@kroah.com> <5fd6003b-55a6-2c3c-9a28-8fd3a575ca78@redhat.com> <20201022104805.GA1503673@kroah.com> <20201022121849.GA1664412@kroah.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <98d9df88-b7ef-fdfb-7d90-2fa7a9d7bab5@redhat.com> Date: Thu, 22 Oct 2020 14:42:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201022121849.GA1664412@kroah.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 22.10.20 14:18, Greg KH wrote: > On Thu, Oct 22, 2020 at 12:48:05PM +0200, Greg KH wrote: >> On Thu, Oct 22, 2020 at 11:36:40AM +0200, David Hildenbrand wrote: >>> On 22.10.20 11:32, David Laight wrote: >>>> From: David Hildenbrand >>>>> Sent: 22 October 2020 10:25 >>>> ... >>>>> ... especially because I recall that clang and gcc behave slightly >>>>> differently: >>>>> >>>>> https://github.com/hjl-tools/x86-psABI/issues/2 >>>>> >>>>> "Function args are different: narrow types are sign or zero extended to >>>>> 32 bits, depending on their type. clang depends on this for incoming >>>>> args, but gcc doesn't make that assumption. But both compilers do it >>>>> when calling, so gcc code can call clang code. >>>> >>>> It really is best to use 'int' (or even 'long') for all numeric >>>> arguments (and results) regardless of the domain of the value. >>>> >>>> Related, I've always worried about 'bool'.... >>>> >>>>> The upper 32 bits of registers are always undefined garbage for types >>>>> smaller than 64 bits." >>>> >>>> On x86-64 the high bits are zeroed by all 32bit loads. >>> >>> Yeah, but does not help here. >>> >>> >>> My thinking: if the compiler that calls import_iovec() has garbage in >>> the upper 32 bit >>> >>> a) gcc will zero it out and not rely on it being zero. >>> b) clang will not zero it out, assuming it is zero. >>> >>> But >>> >>> a) will zero it out when calling the !inlined variant >>> b) clang will zero it out when calling the !inlined variant >>> >>> When inlining, b) strikes. We access garbage. That would mean that we >>> have calling code that's not generated by clang/gcc IIUC. >>> >>> We can test easily by changing the parameters instead of adding an "inline". >> >> Let me try that as well, as I seem to have a good reproducer, but it >> takes a while to run... > > Ok, that didn't work. > > And I can't seem to "fix" this by adding noinline to patches further > along in the patch series (because this commit's function is no longer > present due to later patches.) We might have the same issues with iovec_from_user() and friends now. > > Will keep digging... > > greg k-h > Might be worth to give this a try, just to see if it's related to garbage in upper 32 bit and the way clang is handling it (might be a BUG in clang, though): diff --git a/include/linux/uio.h b/include/linux/uio.h index 72d88566694e..7527298c6b56 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -267,7 +267,7 @@ size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp, struct iov_iter *i); struct iovec *iovec_from_user(const struct iovec __user *uvector, - unsigned long nr_segs, unsigned long fast_segs, + unsigned nr_segs, unsigned fast_segs, struct iovec *fast_iov, bool compat); ssize_t import_iovec(int type, const struct iovec __user *uvec, unsigned nr_segs, unsigned fast_segs, struct iovec **iovp, diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 1635111c5bd2..58417f1916dc 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1652,7 +1652,7 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags) EXPORT_SYMBOL(dup_iter); static int copy_compat_iovec_from_user(struct iovec *iov, - const struct iovec __user *uvec, unsigned long nr_segs) + const struct iovec __user *uvec, unsigned nr_segs) { const struct compat_iovec __user *uiov = (const struct compat_iovec __user *)uvec; @@ -1684,7 +1684,7 @@ static int copy_compat_iovec_from_user(struct iovec *iov, } static int copy_iovec_from_user(struct iovec *iov, - const struct iovec __user *uvec, unsigned long nr_segs) + const struct iovec __user *uvec, unsigned nr_segs) { unsigned long seg; @@ -1699,7 +1699,7 @@ static int copy_iovec_from_user(struct iovec *iov, } struct iovec *iovec_from_user(const struct iovec __user *uvec, - unsigned long nr_segs, unsigned long fast_segs, + unsigned nr_segs, unsigned fast_segs, struct iovec *fast_iov, bool compat) { struct iovec *iov = fast_iov; @@ -1738,7 +1738,7 @@ ssize_t __import_iovec(int type, const struct iovec __user *uvec, struct iov_iter *i, bool compat) { ssize_t total_len = 0; - unsigned long seg; + unsigned seg; struct iovec *iov; iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat); -- Thanks, David / dhildenb