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 18 long __weak probe_kernel_read(void *dst, const void *src, size_t size) 19 __attribute__((alias("__probe_kernel_read"))); 20 21 long __probe_kernel_read(void *dst, const void *src, size_t size) 22 { 23 long ret; 24 mm_segment_t old_fs = get_fs(); 25 26 set_fs(KERNEL_DS); 27 pagefault_disable(); 28 ret = __copy_from_user_inatomic(dst, 29 (__force const void __user *)src, size); 30 pagefault_enable(); 31 set_fs(old_fs); 32 33 return ret ? -EFAULT : 0; 34 } 35 EXPORT_SYMBOL_GPL(probe_kernel_read); 36 37 /** 38 * probe_kernel_write(): safely attempt to write to a location 39 * @dst: address to write to 40 * @src: pointer to the data that shall be written 41 * @size: size of the data chunk 42 * 43 * Safely write to address @dst from the buffer at @src. If a kernel fault 44 * happens, handle that and return -EFAULT. 45 */ 46 long __weak probe_kernel_write(void *dst, const void *src, size_t size) 47 __attribute__((alias("__probe_kernel_write"))); 48 49 long __probe_kernel_write(void *dst, const void *src, size_t size) 50 { 51 long ret; 52 mm_segment_t old_fs = get_fs(); 53 54 set_fs(KERNEL_DS); 55 pagefault_disable(); 56 ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); 57 pagefault_enable(); 58 set_fs(old_fs); 59 60 return ret ? -EFAULT : 0; 61 } 62 EXPORT_SYMBOL_GPL(probe_kernel_write); 63 64 /** 65 * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. 66 * @dst: Destination address, in kernel space. This buffer must be at 67 * least @count bytes long. 68 * @src: Unsafe address. 69 * @count: Maximum number of bytes to copy, including the trailing NUL. 70 * 71 * Copies a NUL-terminated string from unsafe address to kernel buffer. 72 * 73 * On success, returns the length of the string INCLUDING the trailing NUL. 74 * 75 * If access fails, returns -EFAULT (some data may have been copied 76 * and the trailing NUL added). 77 * 78 * If @count is smaller than the length of the string, copies @count-1 bytes, 79 * sets the last byte of @dst buffer to NUL and returns @count. 80 */ 81 long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) 82 { 83 mm_segment_t old_fs = get_fs(); 84 const void *src = unsafe_addr; 85 long ret; 86 87 if (unlikely(count <= 0)) 88 return 0; 89 90 set_fs(KERNEL_DS); 91 pagefault_disable(); 92 93 do { 94 ret = __copy_from_user_inatomic(dst++, 95 (const void __user __force *)src++, 1); 96 } while (dst[-1] && ret == 0 && src - unsafe_addr < count); 97 98 dst[-1] = '\0'; 99 pagefault_enable(); 100 set_fs(old_fs); 101 102 return ret < 0 ? ret : src - unsafe_addr; 103 } 104