Commit 3d708182 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

uaccess: Add non-pagefault user-space read functions 

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
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.

Link: http://lkml.kernel.org/r/155789869802.26965.4940338412595759063.stgit@devnote2



Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 2d8d8fac

include/linux/uaccess.h

+14 −0
Original line number Diff line number Diff line
@@ -242,6 +242,17 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, 
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
@@ -255,6 +266,9 @@ 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

mm/maccess.c

+116 −6
Original line number Diff line number Diff line
@@ -5,8 +5,20 @@ 
#include <linux/mm.h>

#include <linux/uaccess.h>



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
@@ -29,16 +41,40 @@ 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();



	set_fs(USER_DS);

	if (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
@@ -66,6 +102,7 @@ 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 +142,76 @@ 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)

 *

 * 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;

}

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