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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 D990DC43381 for ; Fri, 1 Mar 2019 02:29:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 92EDE218AE for ; Fri, 1 Mar 2019 02:29:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551407362; bh=jJdgpX1L47vSLflN1xQQdcVG1MpizQEHl3YKACjxcmI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=GYrd1g0GsbsbeA2DzFs+lJwGH/Hr586hDLSs9qF+iyygQRh2F1KHoiCN2T0k7CDY8 LAZFDgZgwFIv/KU2nB9hS4v/H23+rcLMBDUEYXLKtAhRQSqCV2/PgUEaKH2NRdOHtp +8tZKL8xlYsDs1nsoT9r/rbgytP8e6XmSLipHd8k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731324AbfCAC3U (ORCPT ); Thu, 28 Feb 2019 21:29:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:34500 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725896AbfCAC3U (ORCPT ); Thu, 28 Feb 2019 21:29:20 -0500 Received: from devnote (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 727B120863; Fri, 1 Mar 2019 02:29:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551407358; bh=jJdgpX1L47vSLflN1xQQdcVG1MpizQEHl3YKACjxcmI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ZFT5RBPhr/4YRUs20kfnwuZH39H+JLOmAPnVABFgLg9cV4Ue5tnbdbrmKYIyUF3tG eKTuaGqfFAXh5ZOA7TymG2vaypwpaHCFDlxs0EBIJt324UI0nSzVpUYiNf4mUFaNxk ReL31c2ZGYKD38hQtNtp1g6FSp1F9S7JqjNseuoE= Date: Fri, 1 Mar 2019 11:29:15 +0900 From: Masami Hiramatsu To: Yonghong Song Cc: Steven Rostedt , Linus Torvalds , "Shuah Khan" , "linux-kernel@vger.kernel.org" , "Andy Lutomirski" , Ingo Molnar , "Andrew Morton" , Changbin Du , Jann Horn , Kees Cook , "Andy Lutomirski" , Alexei Starovoitov , Nadav Amit , "Peter Zijlstra" , Joel Fernandes Subject: Re: [PATCH v5 3/6] uaccess: Add non-pagefault user-space read functions Message-Id: <20190301112915.f00e5d5c894f73da50746bcf@kernel.org> In-Reply-To: <40eae910-16f3-8c6f-6cc7-c52b77b30ccd@fb.com> References: <155136974478.2968.3105123100519786079.stgit@devbox> <155136983467.2968.13980231890937828195.stgit@devbox> <40eae910-16f3-8c6f-6cc7-c52b77b30ccd@fb.com> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Yonghong, On Thu, 28 Feb 2019 22:49:43 +0000 Yonghong Song wrote: > > > On 2/28/19 8:03 AM, Masami Hiramatsu wrote: > > Add probe_user_read(), strncpy_from_unsafe_user() and > > strnlen_unsafe_user() which allows caller to access user-space > > in IRQ context. > > > > Current probe_kernel_read() and strncpy_from_unsafe() are > > not available for user-space memory, because it sets > > KERNEL_DS while accessing data. On some arch, user address > > space and kernel address space can be co-exist, but others > > can not. In that case, setting KERNEL_DS means given > > Just curious. Given the list of arch's currently linux supports, > do you know which arch's fall into "user address space and > kernel address space" can co-exist, and which arch's cannot? As far as I can heard, (and based on probe_kernel_read() failure) sparc32 (and sparc64?), arm64, and s390 will not work. x86 works, but if user patch the 4G/4G, it shouldn't work. Thank you, > > Thanks! > > Yonghong > > > > address is treated as a kernel address space. > > Also strnlen_user() is only available from user context since > > it can sleep if pagefault is enabled. > > > > To access user-space memory without pagefault, we need > > these new functions which sets USER_DS while accessing > > the data. > > > > Signed-off-by: Masami Hiramatsu > > --- > > Changes in v5: > > - Simplify probe_user_read() (Thanks, Peter!) > > - Add strnlen_unsafe_user() > > Changes in v3: > > - Use user_access_ok() for probe_user_read(). > > Changes in v2: > > - Simplify strncpy_from_unsafe_user() using strncpy_from_user() > > according to Linus's suggestion. > > - Simplify probe_user_read() not using intermediate function. > > --- > > include/linux/uaccess.h | 14 +++++ > > mm/maccess.c | 122 +++++++++++++++++++++++++++++++++++++++++++++-- > > 2 files changed, 130 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h > > index 1afd9dfabe67..5be7f9adb418 100644 > > --- a/include/linux/uaccess.h > > +++ b/include/linux/uaccess.h > > @@ -258,6 +258,17 @@ extern long probe_kernel_read(void *dst, const void *src, size_t size); > > extern long __probe_kernel_read(void *dst, const void *src, size_t size); > > > > /* > > + * probe_user_read(): safely attempt to read from a location in user space > > + * @dst: pointer to the buffer that shall take the data > > + * @src: address to read from > > + * @size: size of the data chunk > > + * > > + * Safely read from address @src to the buffer at @dst. If a kernel fault > > + * happens, handle that and return -EFAULT. > > + */ > > +extern long probe_user_read(void *dst, const void __user *src, size_t size); > > + > > +/* > > * probe_kernel_write(): safely attempt to write to a location > > * @dst: address to write to > > * @src: pointer to the data that shall be written > > @@ -270,6 +281,9 @@ extern long notrace probe_kernel_write(void *dst, const void *src, size_t size); > > extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size); > > > > extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count); > > +extern long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr, > > + long count); > > +extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count); > > > > /** > > * probe_kernel_address(): safely attempt to read from a location > > diff --git a/mm/maccess.c b/mm/maccess.c > > index ec00be51a24f..d1b2ec78d9ef 100644 > > --- a/mm/maccess.c > > +++ b/mm/maccess.c > > @@ -5,8 +5,20 @@ > > #include > > #include > > > > +static __always_inline long > > +probe_read_common(void *dst, const void __user *src, size_t size) > > +{ > > + long ret; > > + > > + pagefault_disable(); > > + ret = __copy_from_user_inatomic(dst, src, size); > > + pagefault_enable(); > > + > > + return ret ? -EFAULT : 0; > > +} > > + > > /** > > - * probe_kernel_read(): safely attempt to read from a location > > + * probe_kernel_read(): safely attempt to read from a kernel-space location > > * @dst: pointer to the buffer that shall take the data > > * @src: address to read from > > * @size: size of the data chunk > > @@ -29,17 +41,45 @@ long __probe_kernel_read(void *dst, const void *src, size_t size) > > mm_segment_t old_fs = get_fs(); > > > > set_fs(KERNEL_DS); > > - pagefault_disable(); > > - ret = __copy_from_user_inatomic(dst, > > - (__force const void __user *)src, size); > > - pagefault_enable(); > > + ret = probe_read_common(dst, (__force const void __user *)src, size); > > set_fs(old_fs); > > > > - return ret ? -EFAULT : 0; > > + return ret; > > } > > EXPORT_SYMBOL_GPL(probe_kernel_read); > > > > /** > > + * probe_user_read(): safely attempt to read from a user-space location > > + * @dst: pointer to the buffer that shall take the data > > + * @src: address to read from. This must be a user address. > > + * @size: size of the data chunk > > + * > > + * Safely read from user address @src to the buffer at @dst. If a kernel fault > > + * happens, handle that and return -EFAULT. > > + */ > > + > > +long __weak probe_user_read(void *dst, const void __user *src, size_t size) > > + __attribute__((alias("__probe_user_read"))); > > + > > +long __probe_user_read(void *dst, const void __user *src, size_t size) > > +{ > > + long ret = -EFAULT; > > + mm_segment_t old_fs = get_fs(); > > + > > + /* > > + * Since this can be called in IRQ context, we carefully set the > > + * USER_DS and use user_access_ok() which checks segment setting > > + * instead of task context. > > + */ > > + set_fs(USER_DS); > > + if (user_access_ok(src, size)) > > + ret = probe_read_common(dst, src, size); > > + set_fs(old_fs); > > + return ret; > > +} > > +EXPORT_SYMBOL_GPL(probe_user_read); > > + > > +/** > > * probe_kernel_write(): safely attempt to write to a location > > * @dst: address to write to > > * @src: pointer to the data that shall be written > > @@ -66,6 +106,7 @@ long __probe_kernel_write(void *dst, const void *src, size_t size) > > } > > EXPORT_SYMBOL_GPL(probe_kernel_write); > > > > + > > /** > > * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. > > * @dst: Destination address, in kernel space. This buffer must be at > > @@ -105,3 +146,72 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) > > > > return ret ? -EFAULT : src - unsafe_addr; > > } > > + > > +/** > > + * strncpy_from_unsafe_user: - Copy a NUL terminated string from unsafe user > > + * address. > > + * @dst: Destination address, in kernel space. This buffer must be at > > + * least @count bytes long. > > + * @unsafe_addr: Unsafe user address. > > + * @count: Maximum number of bytes to copy, including the trailing NUL. > > + * > > + * Copies a NUL-terminated string from unsafe user address to kernel buffer. > > + * > > + * On success, returns the length of the string INCLUDING the trailing NUL. > > + * > > + * If access fails, returns -EFAULT (some data may have been copied > > + * and the trailing NUL added). > > + * > > + * If @count is smaller than the length of the string, copies @count-1 bytes, > > + * sets the last byte of @dst buffer to NUL and returns @count. > > + */ > > +long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr, > > + long count) > > +{ > > + mm_segment_t old_fs = get_fs(); > > + long ret; > > + > > + if (unlikely(count <= 0)) > > + return 0; > > + > > + set_fs(USER_DS); > > + pagefault_disable(); > > + ret = strncpy_from_user(dst, unsafe_addr, count); > > + pagefault_enable(); > > + set_fs(old_fs); > > + if (ret >= count) { > > + ret = count; > > + dst[ret - 1] = '\0'; > > + } else if (ret > 0) > > + ret++; > > + return ret; > > +} > > + > > +/** > > + * strnlen_unsafe_user: - Get the size of a user string INCLUDING final NUL. > > + * @unsafe_addr: The string to measure. > > + * @count: Maximum count (including NUL character) > > + * > > + * Get the size of a NUL-terminated string in user space without pagefault. > > + * > > + * Returns the size of the string INCLUDING the terminating NUL. > > + * > > + * If the string is too long, returns a number larger than @count. User > > + * has to check the return value against "> count". > > + * On exception (or invalid count), returns 0. > > + * > > + * Unlike strnlen_user, this can be used from IRQ handler etc. because > > + * it disables pagefaults. > > + */ > > +long strnlen_unsafe_user(const void __user *unsafe_addr, long count) > > +{ > > + mm_segment_t old_fs = get_fs(); > > + int ret; > > + > > + set_fs(USER_DS); > > + pagefault_disable(); > > + ret = strnlen_user(unsafe_addr, count); > > + pagefault_enable(); > > + set_fs(old_fs); > > + return ret; > > +} > > -- Masami Hiramatsu