1 files changed, 254 insertions, 0 deletions
diff --git a/mm/maccess.c b/mm/maccess.c
new file mode 100644
index 000000000..6e41ba452
--- /dev/null
+++ b/mm/maccess.c
@@ -0,0 +1,254 @@
+/*
+ * Access kernel memory without faulting.
+ */
+#include <linux/export.h>
+#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;
+}
+
+static __always_inline long
+probe_write_common(void __user *dst, const void *src, size_t size)
+{
+	long ret;
+
+	pagefault_disable();
+	ret = __copy_to_user_inatomic(dst, src, size);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
+/**
+ * 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
+ *
+ * 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);
+	ret = probe_read_common(dst, (__force const void __user *)src, size);
+	set_fs(old_fs);
+
+	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(VERIFY_READ, 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
+ * @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);
+	ret = probe_write_common((__force void __user *)dst, src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(probe_kernel_write);
+
+/**
+ * probe_user_write(): safely attempt to write to a user-space 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_user_write(void __user *dst, const void *src, size_t size)
+    __attribute__((alias("__probe_user_write")));
+
+long __probe_user_write(void __user *dst, const void *src, size_t size)
+{
+	long ret = -EFAULT;
+	mm_segment_t old_fs = get_fs();
+
+	set_fs(USER_DS);
+	if (access_ok(VERIFY_WRITE, dst, size))
+		ret = probe_write_common(dst, src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(probe_user_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.
+ * @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 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 = __get_user(*dst++, (const char __user __force *)src++);
+	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
+
+	dst[-1] = '\0';
+	pagefault_enable();
+	set_fs(old_fs);
+
+	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;
+}