From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 75/93] maccess: clarify kerneldoc comments Date: Mon, 08 Jun 2020 21:34:07 -0700 Message-ID: <20200609043407.0_Fv4GM3y%akpm@linux-foundation.org> References: <20200608212922.5b7fa74ca3f4e2444441b7f9@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:57890 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726449AbgFIEeK (ORCPT ); Tue, 9 Jun 2020 00:34:10 -0400 In-Reply-To: <20200608212922.5b7fa74ca3f4e2444441b7f9@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, ast@kernel.org, daniel@iogearbox.net, hch@lst.de, hpa@zytor.com, linux-mm@kvack.org, mhiramat@kernel.org, mingo@elte.hu, mm-commits@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org From: Christoph Hellwig Subject: maccess: clarify kerneldoc comments Add proper kerneldoc comments for probe_kernel_read_strict and probe_kernel_read strncpy_from_unsafe_strict and explain the different versus the non-strict version. Link: http://lkml.kernel.org/r/20200521152301.2587579-5-hch@lst.de Signed-off-by: Christoph Hellwig Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Masami Hiramatsu Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- mm/maccess.c | 60 +++++++++++++++++++++++++++++++++++-------------- 1 file changed, 43 insertions(+), 17 deletions(-) --- a/mm/maccess.c~maccess-clarify-kerneldoc-comments +++ a/mm/maccess.c @@ -31,29 +31,36 @@ probe_write_common(void __user *dst, con } /** - * probe_kernel_read(): safely attempt to read from a kernel-space location + * probe_kernel_read(): safely attempt to read from any location * @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. + * Same as probe_kernel_read_strict() except that for architectures with + * not fully separated user and kernel address spaces this function also works + * for user address tanges. + * + * DO NOT USE THIS FUNCTION - it is broken on architectures with entirely + * separate kernel and user address spaces, and also a bad idea otherwise. + */ +long __weak probe_kernel_read(void *dst, const void *src, size_t size) + __attribute__((alias("__probe_kernel_read"))); + +/** + * probe_kernel_read_strict(): safely attempt to read from kernel-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 kernel address @src to the buffer at @dst. If a kernel + * fault happens, handle that and return -EFAULT. * * We ensure that the copy_from_user is executed in atomic context so that * do_page_fault() doesn't attempt to take mmap_lock. This makes * probe_kernel_read() suitable for use within regions where the caller * already holds mmap_lock, or other locks which nest inside mmap_lock. - * - * probe_kernel_read_strict() is the same as probe_kernel_read() except for - * the case where architectures have non-overlapping user and kernel address - * ranges: probe_kernel_read_strict() will additionally return -EFAULT for - * probing memory on a user address range where probe_user_read() is supposed - * to be used instead. */ -long __weak probe_kernel_read(void *dst, const void *src, size_t size) - __attribute__((alias("__probe_kernel_read"))); - long __weak probe_kernel_read_strict(void *dst, const void *src, size_t size) __attribute__((alias("__probe_kernel_read"))); @@ -154,15 +161,34 @@ EXPORT_SYMBOL_GPL(probe_user_write); * 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. * - * strncpy_from_unsafe_strict() is the same as strncpy_from_unsafe() except - * for the case where architectures have non-overlapping user and kernel address - * ranges: strncpy_from_unsafe_strict() will additionally return -EFAULT for - * probing memory on a user address range where strncpy_from_unsafe_user() is - * supposed to be used instead. + * Same as strncpy_from_unsafe_strict() except that for architectures with + * not fully separated user and kernel address spaces this function also works + * for user address tanges. + * + * DO NOT USE THIS FUNCTION - it is broken on architectures with entirely + * separate kernel and user address spaces, and also a bad idea otherwise. */ long __weak strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) __attribute__((alias("__strncpy_from_unsafe"))); +/** + * strncpy_from_unsafe_strict: - Copy a NUL terminated string from unsafe + * address. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @unsafe_addr: Unsafe address. + * @count: Maximum number of bytes to copy, including the trailing NUL. + * + * Copies a NUL-terminated string from unsafe 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 __weak strncpy_from_unsafe_strict(char *dst, const void *unsafe_addr, long count) __attribute__((alias("__strncpy_from_unsafe"))); _