usercopy: Enhance and rename report_usercopy()

In preparation for refactoring the usercopy checks to pass offset to
the hardened usercopy report, this renames report_usercopy() to the
more accurate usercopy_abort(), marks it as noreturn because it is,
adds a hopefully helpful comment for anyone investigating such reports,
makes the function available to the slab allocators, and adds new "detail"
and "offset" arguments.

Signed-off-by: Kees Cook <keescook@chromium.org>

include/linux/uaccess.h

@@ -273,4 +273,10 @@ extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
 #define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0)
 #endif
 
+#ifdef CONFIG_HARDENED_USERCOPY
+void __noreturn usercopy_abort(const char *name, const char *detail,
+			       bool to_user, unsigned long offset,
+			       unsigned long len);
+#endif
+
 #endif		/* __LINUX_UACCESS_H__ */