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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 CB0CFC4346A for ; Mon, 21 Sep 2020 15:02:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A377020758 for ; Mon, 21 Sep 2020 15:02:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727265AbgIUPC1 (ORCPT ); Mon, 21 Sep 2020 11:02:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46594 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727231AbgIUPC0 (ORCPT ); Mon, 21 Sep 2020 11:02:26 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 724C2C061755; Mon, 21 Sep 2020 08:02:26 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKNKV-003BjE-Jk; Mon, 21 Sep 2020 15:02:11 +0000 Date: Mon, 21 Sep 2020 16:02:11 +0100 From: Al Viro To: Christoph Hellwig Cc: Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , David Laight , 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 Subject: Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw() Message-ID: <20200921150211.GS3421308@ZenIV.linux.org.uk> References: <20200921143434.707844-1-hch@lst.de> <20200921143434.707844-3-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200921143434.707844-3-hch@lst.de> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Sep 21, 2020 at 04:34:25PM +0200, Christoph Hellwig wrote: > From: David Laight > > This is the only direct call of rw_copy_check_uvector(). Removing it > will allow rw_copy_check_uvector() to be inlined into import_iovec(), > while only paying a minor price by setting up an otherwise unused > iov_iter in the process_vm_readv/process_vm_writev syscalls that aren't > in a super hot path. > @@ -443,7 +443,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction, > const struct iovec *iov, unsigned long nr_segs, > size_t count) > { > - WARN_ON(direction & ~(READ | WRITE)); > + WARN_ON(direction & ~(READ | WRITE | CHECK_IOVEC_ONLY)); > direction &= READ | WRITE; Ugh... > - rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, > - iovstack_r, &iov_r); > + rc = import_iovec(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, &iov_r, > + &iter_r); > if (rc <= 0) > goto free_iovecs; > > - rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write); > + rc = process_vm_rw_core(pid, &iter_l, iter_r.iov, iter_r.nr_segs, > + flags, vm_write); ... and ugh^2, since now you are not only setting a meaningless iov_iter, you are creating a new place that pokes directly into struct iov_iter guts. Sure, moving rw_copy_check_uvector() over to lib/iov_iter.c makes sense. But I would rather split the access_ok()-related checks out of that thing and bury CHECK_IOVEC_ONLY. Step 1: move the damn thing to lib/iov_iter.c (same as you do, but without making it static) Step 2: split it in two: ssize_t rw_copy_check_uvector(const struct iovec __user * uvector, unsigned long nr_segs, unsigned long fast_segs, struct iovec *fast_pointer, struct iovec **ret_pointer) { unsigned long seg; ssize_t ret; struct iovec *iov = fast_pointer; *ret_pointer = fast_pointer; /* * SuS says "The readv() function *may* fail if the iovcnt argument * was less than or equal to 0, or greater than {IOV_MAX}. Linux has * traditionally returned zero for zero segments, so... */ if (nr_segs == 0) return 0; /* * First get the "struct iovec" from user memory and * verify all the pointers */ if (nr_segs > UIO_MAXIOV) return -EINVAL; if (nr_segs > fast_segs) { iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL); if (!iov) return -ENOMEM; *ret_pointer = iov; } if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) return -EFAULT; /* * According to the Single Unix Specification we should return EINVAL * if an element length is < 0 when cast to ssize_t or if the * total length would overflow the ssize_t return value of the * system call. * * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the * overflow case. */ ret = 0; for (seg = 0; seg < nr_segs; seg++) { void __user *buf = iov[seg].iov_base; ssize_t len = (ssize_t)iov[seg].iov_len; /* see if we we're about to use an invalid len or if * it's about to overflow ssize_t */ if (len < 0) return -EINVAL; if (len > MAX_RW_COUNT - ret) { len = MAX_RW_COUNT - ret; iov[seg].iov_len = len; } ret += len; } return ret; } /* * This is merely an early sanity check; we do _not_ rely upon * it when we get to the actual memory accesses. */ static bool check_iovecs(const struct iovec *iov, int nr_segs) { for (seg = 0; seg < nr_segs; seg++) { void __user *buf = iov[seg].iov_base; ssize_t len = (ssize_t)iov[seg].iov_len; if (unlikely(!access_ok(buf, len))) return false; } return true; } ssize_t import_iovec(int type, const struct iovec __user * uvector, unsigned nr_segs, unsigned fast_segs, struct iovec **iov, struct iov_iter *i) { struct iovec *p; ssize_t n; n = rw_copy_check_uvector(uvector, nr_segs, fast_segs, *iov, &p); if (n > 0 && !check_iovecs(p, nr_segs)) n = -EFAULT; if (n < 0) { if (p != *iov) kfree(p); *iov = NULL; return n; } iov_iter_init(i, type, p, nr_segs, n); *iov = p == *iov ? NULL : p; return n; } kill CHECK_IOVEC_ONLY and use rw_copy_check_uvector() without the type argument in mm/process_vm_access.c Saner that way, IMO...