1c33fa9f5SIngo Molnar /* 2c33fa9f5SIngo Molnar * Access kernel memory without faulting. 3c33fa9f5SIngo Molnar */ 4b95f1b31SPaul Gortmaker #include <linux/export.h> 5c33fa9f5SIngo Molnar #include <linux/mm.h> 67c7fcf76SDavid Howells #include <linux/uaccess.h> 7c33fa9f5SIngo Molnar 8c33fa9f5SIngo Molnar /** 9c33fa9f5SIngo Molnar * probe_kernel_read(): safely attempt to read from a location 10c33fa9f5SIngo Molnar * @dst: pointer to the buffer that shall take the data 11c33fa9f5SIngo Molnar * @src: address to read from 12c33fa9f5SIngo Molnar * @size: size of the data chunk 13c33fa9f5SIngo Molnar * 14c33fa9f5SIngo Molnar * Safely read from address @src to the buffer at @dst. If a kernel fault 15c33fa9f5SIngo Molnar * happens, handle that and return -EFAULT. 160ab32b6fSAndrew Morton * 170ab32b6fSAndrew Morton * We ensure that the copy_from_user is executed in atomic context so that 180ab32b6fSAndrew Morton * do_page_fault() doesn't attempt to take mmap_sem. This makes 190ab32b6fSAndrew Morton * probe_kernel_read() suitable for use within regions where the caller 200ab32b6fSAndrew Morton * already holds mmap_sem, or other locks which nest inside mmap_sem. 21c33fa9f5SIngo Molnar */ 226144a85aSJason Wessel 23f29c5041SSteven Rostedt long __weak probe_kernel_read(void *dst, const void *src, size_t size) 246144a85aSJason Wessel __attribute__((alias("__probe_kernel_read"))); 256144a85aSJason Wessel 26f29c5041SSteven Rostedt long __probe_kernel_read(void *dst, const void *src, size_t size) 27c33fa9f5SIngo Molnar { 28c33fa9f5SIngo Molnar long ret; 29b4b8ac52SJason Wessel mm_segment_t old_fs = get_fs(); 30c33fa9f5SIngo Molnar 31b4b8ac52SJason Wessel set_fs(KERNEL_DS); 32c33fa9f5SIngo Molnar pagefault_disable(); 33c33fa9f5SIngo Molnar ret = __copy_from_user_inatomic(dst, 34c33fa9f5SIngo Molnar (__force const void __user *)src, size); 35c33fa9f5SIngo Molnar pagefault_enable(); 36b4b8ac52SJason Wessel set_fs(old_fs); 37c33fa9f5SIngo Molnar 38c33fa9f5SIngo Molnar return ret ? -EFAULT : 0; 39c33fa9f5SIngo Molnar } 40c33fa9f5SIngo Molnar EXPORT_SYMBOL_GPL(probe_kernel_read); 41c33fa9f5SIngo Molnar 42c33fa9f5SIngo Molnar /** 43c33fa9f5SIngo Molnar * probe_kernel_write(): safely attempt to write to a location 44c33fa9f5SIngo Molnar * @dst: address to write to 45c33fa9f5SIngo Molnar * @src: pointer to the data that shall be written 46c33fa9f5SIngo Molnar * @size: size of the data chunk 47c33fa9f5SIngo Molnar * 48c33fa9f5SIngo Molnar * Safely write to address @dst from the buffer at @src. If a kernel fault 49c33fa9f5SIngo Molnar * happens, handle that and return -EFAULT. 50c33fa9f5SIngo Molnar */ 51f29c5041SSteven Rostedt long __weak probe_kernel_write(void *dst, const void *src, size_t size) 526144a85aSJason Wessel __attribute__((alias("__probe_kernel_write"))); 536144a85aSJason Wessel 54f29c5041SSteven Rostedt long __probe_kernel_write(void *dst, const void *src, size_t size) 55c33fa9f5SIngo Molnar { 56c33fa9f5SIngo Molnar long ret; 57b4b8ac52SJason Wessel mm_segment_t old_fs = get_fs(); 58c33fa9f5SIngo Molnar 59b4b8ac52SJason Wessel set_fs(KERNEL_DS); 60c33fa9f5SIngo Molnar pagefault_disable(); 61c33fa9f5SIngo Molnar ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); 62c33fa9f5SIngo Molnar pagefault_enable(); 63b4b8ac52SJason Wessel set_fs(old_fs); 64c33fa9f5SIngo Molnar 65c33fa9f5SIngo Molnar return ret ? -EFAULT : 0; 66c33fa9f5SIngo Molnar } 67c33fa9f5SIngo Molnar EXPORT_SYMBOL_GPL(probe_kernel_write); 68dbb7ee0eSAlexei Starovoitov 69dbb7ee0eSAlexei Starovoitov /** 70dbb7ee0eSAlexei Starovoitov * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. 71dbb7ee0eSAlexei Starovoitov * @dst: Destination address, in kernel space. This buffer must be at 72dbb7ee0eSAlexei Starovoitov * least @count bytes long. 73dbb7ee0eSAlexei Starovoitov * @src: Unsafe address. 74dbb7ee0eSAlexei Starovoitov * @count: Maximum number of bytes to copy, including the trailing NUL. 75dbb7ee0eSAlexei Starovoitov * 76dbb7ee0eSAlexei Starovoitov * Copies a NUL-terminated string from unsafe address to kernel buffer. 77dbb7ee0eSAlexei Starovoitov * 78dbb7ee0eSAlexei Starovoitov * On success, returns the length of the string INCLUDING the trailing NUL. 79dbb7ee0eSAlexei Starovoitov * 80dbb7ee0eSAlexei Starovoitov * If access fails, returns -EFAULT (some data may have been copied 81dbb7ee0eSAlexei Starovoitov * and the trailing NUL added). 82dbb7ee0eSAlexei Starovoitov * 83dbb7ee0eSAlexei Starovoitov * If @count is smaller than the length of the string, copies @count-1 bytes, 84dbb7ee0eSAlexei Starovoitov * sets the last byte of @dst buffer to NUL and returns @count. 85dbb7ee0eSAlexei Starovoitov */ 86dbb7ee0eSAlexei Starovoitov long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) 87dbb7ee0eSAlexei Starovoitov { 88dbb7ee0eSAlexei Starovoitov mm_segment_t old_fs = get_fs(); 89dbb7ee0eSAlexei Starovoitov const void *src = unsafe_addr; 90dbb7ee0eSAlexei Starovoitov long ret; 91dbb7ee0eSAlexei Starovoitov 92dbb7ee0eSAlexei Starovoitov if (unlikely(count <= 0)) 93dbb7ee0eSAlexei Starovoitov return 0; 94dbb7ee0eSAlexei Starovoitov 95dbb7ee0eSAlexei Starovoitov set_fs(KERNEL_DS); 96dbb7ee0eSAlexei Starovoitov pagefault_disable(); 97dbb7ee0eSAlexei Starovoitov 98dbb7ee0eSAlexei Starovoitov do { 99dbb7ee0eSAlexei Starovoitov ret = __copy_from_user_inatomic(dst++, 100dbb7ee0eSAlexei Starovoitov (const void __user __force *)src++, 1); 101dbb7ee0eSAlexei Starovoitov } while (dst[-1] && ret == 0 && src - unsafe_addr < count); 102dbb7ee0eSAlexei Starovoitov 103dbb7ee0eSAlexei Starovoitov dst[-1] = '\0'; 104dbb7ee0eSAlexei Starovoitov pagefault_enable(); 105dbb7ee0eSAlexei Starovoitov set_fs(old_fs); 106dbb7ee0eSAlexei Starovoitov 1079dd861d5SRasmus Villemoes return ret ? -EFAULT : src - unsafe_addr; 108dbb7ee0eSAlexei Starovoitov } 109