linux/mm/maccess.c
Andrew Morton 0ab32b6f1b uaccess: reimplement probe_kernel_address() using probe_kernel_read()
probe_kernel_address() is basically the same as the (later added)
probe_kernel_read().

The return value on EFAULT is a bit different: probe_kernel_address()
returns number-of-bytes-not-copied whereas probe_kernel_read() returns
-EFAULT.  All callers have been checked, none cared.

probe_kernel_read() can be overridden by the architecture whereas
probe_kernel_address() cannot.  parisc, blackfin and um do this, to insert
additional checking.  Hence this patch possibly fixes obscure bugs,
although there are only two probe_kernel_address() callsites outside
arch/.

My first attempt involved removing probe_kernel_address() entirely and
converting all callsites to use probe_kernel_read() directly, but that got
tiresome.

This patch shrinks mm/slab_common.o by 218 bytes.  For a single
probe_kernel_address() callsite.

Cc: Steven Miao <realmz6@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-05 19:34:48 -08:00

109 lines
3.1 KiB
C

/*
* Access kernel memory without faulting.
*/
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
/**
* probe_kernel_read(): safely attempt to read from a 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.
*
* 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.
*/
long __weak probe_kernel_read(void *dst, const void *src, size_t size)
__attribute__((alias("__probe_kernel_read")));
long __probe_kernel_read(void *dst, const void *src, size_t size)
{
long ret;
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();
set_fs(old_fs);
return ret ? -EFAULT : 0;
}
EXPORT_SYMBOL_GPL(probe_kernel_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
* @size: size of the data chunk
*
* Safely write to address @dst from the buffer at @src. If a kernel fault
* happens, handle that and return -EFAULT.
*/
long __weak probe_kernel_write(void *dst, const void *src, size_t size)
__attribute__((alias("__probe_kernel_write")));
long __probe_kernel_write(void *dst, const void *src, size_t size)
{
long ret;
mm_segment_t old_fs = get_fs();
set_fs(KERNEL_DS);
pagefault_disable();
ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
pagefault_enable();
set_fs(old_fs);
return ret ? -EFAULT : 0;
}
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
* least @count bytes long.
* @src: 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 strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
{
mm_segment_t old_fs = get_fs();
const void *src = unsafe_addr;
long ret;
if (unlikely(count <= 0))
return 0;
set_fs(KERNEL_DS);
pagefault_disable();
do {
ret = __copy_from_user_inatomic(dst++,
(const void __user __force *)src++, 1);
} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
dst[-1] = '\0';
pagefault_enable();
set_fs(old_fs);
return ret < 0 ? ret : src - unsafe_addr;
}