1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Access kernel memory without faulting. 4 */ 5 #include <linux/export.h> 6 #include <linux/mm.h> 7 #include <linux/uaccess.h> 8 9 /** 10 * probe_kernel_read(): safely attempt to read from a location 11 * @dst: pointer to the buffer that shall take the data 12 * @src: address to read from 13 * @size: size of the data chunk 14 * 15 * Safely read from address @src to the buffer at @dst. If a kernel fault 16 * happens, handle that and return -EFAULT. 17 * 18 * We ensure that the copy_from_user is executed in atomic context so that 19 * do_page_fault() doesn't attempt to take mmap_sem. This makes 20 * probe_kernel_read() suitable for use within regions where the caller 21 * already holds mmap_sem, or other locks which nest inside mmap_sem. 22 */ 23 24 long __weak probe_kernel_read(void *dst, const void *src, size_t size) 25 __attribute__((alias("__probe_kernel_read"))); 26 27 long __probe_kernel_read(void *dst, const void *src, size_t size) 28 { 29 long ret; 30 mm_segment_t old_fs = get_fs(); 31 32 set_fs(KERNEL_DS); 33 pagefault_disable(); 34 ret = __copy_from_user_inatomic(dst, 35 (__force const void __user *)src, size); 36 pagefault_enable(); 37 set_fs(old_fs); 38 39 return ret ? -EFAULT : 0; 40 } 41 EXPORT_SYMBOL_GPL(probe_kernel_read); 42 43 /** 44 * probe_kernel_write(): safely attempt to write to a location 45 * @dst: address to write to 46 * @src: pointer to the data that shall be written 47 * @size: size of the data chunk 48 * 49 * Safely write to address @dst from the buffer at @src. If a kernel fault 50 * happens, handle that and return -EFAULT. 51 */ 52 long __weak probe_kernel_write(void *dst, const void *src, size_t size) 53 __attribute__((alias("__probe_kernel_write"))); 54 55 long __probe_kernel_write(void *dst, const void *src, size_t size) 56 { 57 long ret; 58 mm_segment_t old_fs = get_fs(); 59 60 set_fs(KERNEL_DS); 61 pagefault_disable(); 62 ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); 63 pagefault_enable(); 64 set_fs(old_fs); 65 66 return ret ? -EFAULT : 0; 67 } 68 EXPORT_SYMBOL_GPL(probe_kernel_write); 69 70 /** 71 * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. 72 * @dst: Destination address, in kernel space. This buffer must be at 73 * least @count bytes long. 74 * @unsafe_addr: Unsafe address. 75 * @count: Maximum number of bytes to copy, including the trailing NUL. 76 * 77 * Copies a NUL-terminated string from unsafe address to kernel buffer. 78 * 79 * On success, returns the length of the string INCLUDING the trailing NUL. 80 * 81 * If access fails, returns -EFAULT (some data may have been copied 82 * and the trailing NUL added). 83 * 84 * If @count is smaller than the length of the string, copies @count-1 bytes, 85 * sets the last byte of @dst buffer to NUL and returns @count. 86 */ 87 long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) 88 { 89 mm_segment_t old_fs = get_fs(); 90 const void *src = unsafe_addr; 91 long ret; 92 93 if (unlikely(count <= 0)) 94 return 0; 95 96 set_fs(KERNEL_DS); 97 pagefault_disable(); 98 99 do { 100 ret = __get_user(*dst++, (const char __user __force *)src++); 101 } while (dst[-1] && ret == 0 && src - unsafe_addr < count); 102 103 dst[-1] = '\0'; 104 pagefault_enable(); 105 set_fs(old_fs); 106 107 return ret ? -EFAULT : src - unsafe_addr; 108 } 109