From: Christoph Hellwig <hch@lst.de>
To: x86@kernel.org, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Masami Hiramatsu <mhiramat@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-parisc@vger.kernel.org, linux-um@lists.infradead.org,
netdev@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: [PATCH 04/20] maccess: clarify kerneldoc comments
Date: Tue, 19 May 2020 15:44:33 +0200 [thread overview]
Message-ID: <20200519134449.1466624-5-hch@lst.de> (raw)
In-Reply-To: <20200519134449.1466624-1-hch@lst.de>
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.
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
mm/maccess.c | 61 ++++++++++++++++++++++++++++++++++++----------------
1 file changed, 43 insertions(+), 18 deletions(-)
diff --git a/mm/maccess.c b/mm/maccess.c
index 4e7f3b6eb05ae..747581ac50dc9 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -31,29 +31,35 @@ probe_write_common(void __user *dst, const void *src, size_t size)
}
/**
- * 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_sem. This makes
* probe_kernel_read() suitable for use within regions where the caller
* already holds mmap_sem, or other locks which nest inside mmap_sem.
- *
- * 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")));
@@ -153,15 +159,34 @@ long probe_user_write(void __user *dst, const void *src, size_t size)
* 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")));
--
2.26.2
next prev parent reply other threads:[~2020-05-19 13:46 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 13:44 clean up and streamline probe_kernel_* and friends v3 Christoph Hellwig
2020-05-19 13:44 ` [PATCH 01/20] maccess: unexport probe_kernel_write and probe_user_write Christoph Hellwig
2020-05-19 13:44 ` [PATCH 02/20] maccess: remove various unused weak aliases Christoph Hellwig
2020-05-19 13:44 ` [PATCH 03/20] maccess: remove duplicate kerneldoc comments Christoph Hellwig
2020-05-19 13:44 ` Christoph Hellwig [this message]
2020-05-19 13:44 ` [PATCH 05/20] maccess: update the top of file comment Christoph Hellwig
2020-05-19 13:44 ` [PATCH 06/20] maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 07/20] maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 08/20] maccess: rename strnlen_unsafe_user to strnlen_user_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 09/20] maccess: remove probe_read_common and probe_write_common Christoph Hellwig
2020-05-19 13:44 ` [PATCH 10/20] maccess: unify the probe kernel arch hooks Christoph Hellwig
2020-05-19 13:44 ` [PATCH 11/20] bpf: factor out a bpf_trace_copy_string helper Christoph Hellwig
2020-05-19 16:07 ` Linus Torvalds
2020-05-19 16:14 ` Christoph Hellwig
2020-05-19 16:36 ` Linus Torvalds
2020-05-19 13:44 ` [PATCH 12/20] maccess: remove strncpy_from_unsafe Christoph Hellwig
2020-05-19 16:25 ` Linus Torvalds
2020-05-19 16:41 ` Christoph Hellwig
2020-05-19 16:46 ` Linus Torvalds
2020-05-19 13:44 ` [PATCH 13/20] maccess: always use strict semantics for probe_kernel_read Christoph Hellwig
2020-05-19 16:33 ` Linus Torvalds
2020-05-20 11:11 ` Masami Hiramatsu
2020-05-20 11:13 ` Christoph Hellwig
2020-05-19 13:44 ` [PATCH 14/20] maccess: move user access routines together Christoph Hellwig
2020-05-19 13:44 ` [PATCH 15/20] maccess: allow architectures to provide kernel probing directly Christoph Hellwig
2020-05-19 13:44 ` [PATCH 16/20] x86: use non-set_fs based maccess routines Christoph Hellwig
2020-05-19 13:44 ` [PATCH 17/20] maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 18/20] maccess: rename probe_user_{read,write} to copy_{from,to}_user_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 19/20] maccess: rename probe_kernel_address to get_kernel_nofault Christoph Hellwig
2020-05-19 13:44 ` [PATCH 20/20] maccess: return -ERANGE when copy_from_kernel_nofault_allowed fails Christoph Hellwig
2020-05-20 11:02 ` Masami Hiramatsu
2020-05-20 16:16 ` Christoph Hellwig
2020-05-19 16:34 ` clean up and streamline probe_kernel_* and friends v3 Linus Torvalds
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