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