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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 014ABC3A5AB for ; Thu, 5 Sep 2019 07:32:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C53962332B for ; Thu, 5 Sep 2019 07:32:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="AJRabzew" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730839AbfIEHci (ORCPT ); Thu, 5 Sep 2019 03:32:38 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:60790 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726032AbfIEHch (ORCPT ); Thu, 5 Sep 2019 03:32:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=4t74LAQ8HoNYAg0doAzYeg6TjlgtY7XOq8PTAR8Aews=; b=AJRabzewRFq+7OIffGLOihagu Q6x11cx7vH4lTSeXsd4sAIih6IBnXO0V0QVaYKYPuOX5IyCWWNG/A5IpMM7XxnP5h6RLlcaHT7zAl Fno/b6maUNUFsIFZfcSZQfkojE92I1guZML9x4l93b6YVf0uAT4pU5Fy9CwtrM/pmFvkV07Tl/NDH UWkPdVlV3t+bv3MIvz+w7aolGCsHgXfQaMgu8S2KGM3coJTlVXl+SJRvUIqp+hXS+wtnXq+q3pBAn iaVF6fnqduZ0Uuod15wKkSs509rKcOJZLU443oqaQooqsVuFFvY8MOtj86gBpYi+ToNnI/idUssy/ WNhx5pafw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i5mFW-0005ul-GL; Thu, 05 Sep 2019 07:32:10 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 73B24306038; Thu, 5 Sep 2019 09:31:28 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 550C129DE6C22; Thu, 5 Sep 2019 09:32:05 +0200 (CEST) Date: Thu, 5 Sep 2019 09:32:05 +0200 From: Peter Zijlstra To: Aleksa Sarai Cc: Al Viro , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Christian Brauner , Rasmus Villemoes , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Aleksa Sarai , Linus Torvalds , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Message-ID: <20190905073205.GY2332@hirez.programming.kicks-ass.net> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904201933.10736-2-cyphar@cyphar.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > +/** > + * copy_struct_to_user: copy a struct to user space > + * @dst: Destination address, in user space. > + * @usize: Size of @dst struct. > + * @src: Source address, in kernel space. > + * @ksize: Size of @src struct. > + * > + * Copies a struct from kernel space to user space, in a way that guarantees > + * backwards-compatibility for struct syscall arguments (as long as future > + * struct extensions are made such that all new fields are *appended* to the > + * old struct, and zeroed-out new fields have the same meaning as the old > + * struct). > + * > + * @ksize is just sizeof(*dst), and @usize should've been passed by user space. > + * The recommended usage is something like the following: > + * > + * SYSCALL_DEFINE2(foobar, struct foo __user *, uarg, size_t, usize) > + * { > + * int err; > + * struct foo karg = {}; > + * > + * // do something with karg > + * > + * err = copy_struct_to_user(uarg, usize, &karg, sizeof(karg)); > + * if (err) > + * return err; > + * > + * // ... > + * } > + * > + * There are three cases to consider: > + * * If @usize == @ksize, then it's copied verbatim. > + * * If @usize < @ksize, then kernel space is "returning" a newer struct to an > + * older user space. In order to avoid user space getting incomplete > + * information (new fields might be important), all trailing bytes in @src > + * (@ksize - @usize) must be zerored s/zerored/zero/, right? > , otherwise -EFBIG is returned. 'Funny' that, copy_struct_from_user() below seems to use E2BIG. > + * * If @usize > @ksize, then the kernel is "returning" an older struct to a > + * newer user space. The trailing bytes in @dst (@usize - @ksize) will be > + * zero-filled. > + * > + * Returns (in all cases, some data may have been copied): > + * * -EFBIG: (@usize < @ksize) and there are non-zero trailing bytes in @src. > + * * -EFAULT: access to user space failed. > + */ > +int copy_struct_to_user(void __user *dst, size_t usize, > + const void *src, size_t ksize) > +{ > + size_t size = min(ksize, usize); > + size_t rest = abs(ksize - usize); > + > + if (unlikely(usize > PAGE_SIZE)) > + return -EFAULT; Not documented above. Implementation consistent with *from*, but see below. > + if (unlikely(!access_ok(dst, usize))) > + return -EFAULT; > + > + /* Deal with trailing bytes. */ > + if (usize < ksize) { > + if (memchr_inv(src + size, 0, rest)) > + return -EFBIG; > + } else if (usize > ksize) { > + if (__memzero_user(dst + size, rest)) > + return -EFAULT; > + } > + /* Copy the interoperable parts of the struct. */ > + if (__copy_to_user(dst, src, size)) > + return -EFAULT; > + return 0; > +} > +EXPORT_SYMBOL(copy_struct_to_user); > + > +/** > + * copy_struct_from_user: copy a struct from user space > + * @dst: Destination address, in kernel space. This buffer must be @ksize > + * bytes long. > + * @ksize: Size of @dst struct. > + * @src: Source address, in user space. > + * @usize: (Alleged) size of @src struct. > + * > + * Copies a struct from user space to kernel space, in a way that guarantees > + * backwards-compatibility for struct syscall arguments (as long as future > + * struct extensions are made such that all new fields are *appended* to the > + * old struct, and zeroed-out new fields have the same meaning as the old > + * struct). > + * > + * @ksize is just sizeof(*dst), and @usize should've been passed by user space. > + * The recommended usage is something like the following: > + * > + * SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize) > + * { > + * int err; > + * struct foo karg = {}; > + * > + * err = copy_struct_from_user(&karg, sizeof(karg), uarg, size); > + * if (err) > + * return err; > + * > + * // ... > + * } > + * > + * There are three cases to consider: > + * * If @usize == @ksize, then it's copied verbatim. > + * * If @usize < @ksize, then the user space has passed an old struct to a > + * newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize) > + * are to be zero-filled. > + * * If @usize > @ksize, then the user space has passed a new struct to an > + * older kernel. The trailing bytes unknown to the kernel (@usize - @ksize) > + * are checked to ensure they are zeroed, otherwise -E2BIG is returned. > + * > + * Returns (in all cases, some data may have been copied): > + * * -E2BIG: (@usize > @ksize) and there are non-zero trailing bytes in @src. > + * * -E2BIG: @usize is "too big" (at time of writing, >PAGE_SIZE). > + * * -EFAULT: access to user space failed. > + */ > +int copy_struct_from_user(void *dst, size_t ksize, > + const void __user *src, size_t usize) > +{ > + size_t size = min(ksize, usize); > + size_t rest = abs(ksize - usize); > + > + if (unlikely(usize > PAGE_SIZE)) > + return -EFAULT; Documented above as returning -E2BIG. > + if (unlikely(!access_ok(src, usize))) > + return -EFAULT; > + > + /* Deal with trailing bytes. */ > + if (usize < ksize) > + memset(dst + size, 0, rest); > + else if (usize > ksize) { > + const void __user *addr = src + size; > + char buffer[BUFFER_SIZE] = {}; Isn't that too big for on-stack? > + > + while (rest > 0) { > + size_t bufsize = min(rest, sizeof(buffer)); > + > + if (__copy_from_user(buffer, addr, bufsize)) > + return -EFAULT; > + if (memchr_inv(buffer, 0, bufsize)) > + return -E2BIG; > + > + addr += bufsize; > + rest -= bufsize; > + } The perf implementation uses get_user(); but if that is too slow, surely we can do something with uaccess_try() here? > + } > + /* Copy the interoperable parts of the struct. */ > + if (__copy_from_user(dst, src, size)) > + return -EFAULT; > + return 0; > +} > +EXPORT_SYMBOL(copy_struct_from_user); And personally I'm not a big fan of EXPORT_SYMBOL().