1*457c8996SThomas Gleixner // SPDX-License-Identifier: GPL-2.0-only 2c33fa9f5SIngo Molnar /* 3c33fa9f5SIngo Molnar * Access kernel memory without faulting. 4c33fa9f5SIngo Molnar */ 5b95f1b31SPaul Gortmaker #include <linux/export.h> 6c33fa9f5SIngo Molnar #include <linux/mm.h> 77c7fcf76SDavid Howells #include <linux/uaccess.h> 8c33fa9f5SIngo Molnar 9c33fa9f5SIngo Molnar /** 10c33fa9f5SIngo Molnar * probe_kernel_read(): safely attempt to read from a location 11c33fa9f5SIngo Molnar * @dst: pointer to the buffer that shall take the data 12c33fa9f5SIngo Molnar * @src: address to read from 13c33fa9f5SIngo Molnar * @size: size of the data chunk 14c33fa9f5SIngo Molnar * 15c33fa9f5SIngo Molnar * Safely read from address @src to the buffer at @dst. If a kernel fault 16c33fa9f5SIngo Molnar * happens, handle that and return -EFAULT. 170ab32b6fSAndrew Morton * 180ab32b6fSAndrew Morton * We ensure that the copy_from_user is executed in atomic context so that 190ab32b6fSAndrew Morton * do_page_fault() doesn't attempt to take mmap_sem. This makes 200ab32b6fSAndrew Morton * probe_kernel_read() suitable for use within regions where the caller 210ab32b6fSAndrew Morton * already holds mmap_sem, or other locks which nest inside mmap_sem. 22c33fa9f5SIngo Molnar */ 236144a85aSJason Wessel 24f29c5041SSteven Rostedt long __weak probe_kernel_read(void *dst, const void *src, size_t size) 256144a85aSJason Wessel __attribute__((alias("__probe_kernel_read"))); 266144a85aSJason Wessel 27f29c5041SSteven Rostedt long __probe_kernel_read(void *dst, const void *src, size_t size) 28c33fa9f5SIngo Molnar { 29c33fa9f5SIngo Molnar long ret; 30b4b8ac52SJason Wessel mm_segment_t old_fs = get_fs(); 31c33fa9f5SIngo Molnar 32b4b8ac52SJason Wessel set_fs(KERNEL_DS); 33c33fa9f5SIngo Molnar pagefault_disable(); 34c33fa9f5SIngo Molnar ret = __copy_from_user_inatomic(dst, 35c33fa9f5SIngo Molnar (__force const void __user *)src, size); 36c33fa9f5SIngo Molnar pagefault_enable(); 37b4b8ac52SJason Wessel set_fs(old_fs); 38c33fa9f5SIngo Molnar 39c33fa9f5SIngo Molnar return ret ? -EFAULT : 0; 40c33fa9f5SIngo Molnar } 41c33fa9f5SIngo Molnar EXPORT_SYMBOL_GPL(probe_kernel_read); 42c33fa9f5SIngo Molnar 43c33fa9f5SIngo Molnar /** 44c33fa9f5SIngo Molnar * probe_kernel_write(): safely attempt to write to a location 45c33fa9f5SIngo Molnar * @dst: address to write to 46c33fa9f5SIngo Molnar * @src: pointer to the data that shall be written 47c33fa9f5SIngo Molnar * @size: size of the data chunk 48c33fa9f5SIngo Molnar * 49c33fa9f5SIngo Molnar * Safely write to address @dst from the buffer at @src. If a kernel fault 50c33fa9f5SIngo Molnar * happens, handle that and return -EFAULT. 51c33fa9f5SIngo Molnar */ 52f29c5041SSteven Rostedt long __weak probe_kernel_write(void *dst, const void *src, size_t size) 536144a85aSJason Wessel __attribute__((alias("__probe_kernel_write"))); 546144a85aSJason Wessel 55f29c5041SSteven Rostedt long __probe_kernel_write(void *dst, const void *src, size_t size) 56c33fa9f5SIngo Molnar { 57c33fa9f5SIngo Molnar long ret; 58b4b8ac52SJason Wessel mm_segment_t old_fs = get_fs(); 59c33fa9f5SIngo Molnar 60b4b8ac52SJason Wessel set_fs(KERNEL_DS); 61c33fa9f5SIngo Molnar pagefault_disable(); 62c33fa9f5SIngo Molnar ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); 63c33fa9f5SIngo Molnar pagefault_enable(); 64b4b8ac52SJason Wessel set_fs(old_fs); 65c33fa9f5SIngo Molnar 66c33fa9f5SIngo Molnar return ret ? -EFAULT : 0; 67c33fa9f5SIngo Molnar } 68c33fa9f5SIngo Molnar EXPORT_SYMBOL_GPL(probe_kernel_write); 69dbb7ee0eSAlexei Starovoitov 70dbb7ee0eSAlexei Starovoitov /** 71dbb7ee0eSAlexei Starovoitov * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. 72dbb7ee0eSAlexei Starovoitov * @dst: Destination address, in kernel space. This buffer must be at 73dbb7ee0eSAlexei Starovoitov * least @count bytes long. 74f144c390SMike Rapoport * @unsafe_addr: Unsafe address. 75dbb7ee0eSAlexei Starovoitov * @count: Maximum number of bytes to copy, including the trailing NUL. 76dbb7ee0eSAlexei Starovoitov * 77dbb7ee0eSAlexei Starovoitov * Copies a NUL-terminated string from unsafe address to kernel buffer. 78dbb7ee0eSAlexei Starovoitov * 79dbb7ee0eSAlexei Starovoitov * On success, returns the length of the string INCLUDING the trailing NUL. 80dbb7ee0eSAlexei Starovoitov * 81dbb7ee0eSAlexei Starovoitov * If access fails, returns -EFAULT (some data may have been copied 82dbb7ee0eSAlexei Starovoitov * and the trailing NUL added). 83dbb7ee0eSAlexei Starovoitov * 84dbb7ee0eSAlexei Starovoitov * If @count is smaller than the length of the string, copies @count-1 bytes, 85dbb7ee0eSAlexei Starovoitov * sets the last byte of @dst buffer to NUL and returns @count. 86dbb7ee0eSAlexei Starovoitov */ 87dbb7ee0eSAlexei Starovoitov long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) 88dbb7ee0eSAlexei Starovoitov { 89dbb7ee0eSAlexei Starovoitov mm_segment_t old_fs = get_fs(); 90dbb7ee0eSAlexei Starovoitov const void *src = unsafe_addr; 91dbb7ee0eSAlexei Starovoitov long ret; 92dbb7ee0eSAlexei Starovoitov 93dbb7ee0eSAlexei Starovoitov if (unlikely(count <= 0)) 94dbb7ee0eSAlexei Starovoitov return 0; 95dbb7ee0eSAlexei Starovoitov 96dbb7ee0eSAlexei Starovoitov set_fs(KERNEL_DS); 97dbb7ee0eSAlexei Starovoitov pagefault_disable(); 98dbb7ee0eSAlexei Starovoitov 99dbb7ee0eSAlexei Starovoitov do { 100bd28b145SLinus Torvalds ret = __get_user(*dst++, (const char __user __force *)src++); 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