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 current->kernel_uaccess_faults_ok++; 34 ret = __copy_from_user_inatomic(dst, 35 (__force const void __user *)src, size); 36 current->kernel_uaccess_faults_ok--; 37 pagefault_enable(); 38 set_fs(old_fs); 39 40 return ret ? -EFAULT : 0; 41 } 42 EXPORT_SYMBOL_GPL(probe_kernel_read); 43 44 /** 45 * probe_kernel_write(): safely attempt to write to a location 46 * @dst: address to write to 47 * @src: pointer to the data that shall be written 48 * @size: size of the data chunk 49 * 50 * Safely write to address @dst from the buffer at @src. If a kernel fault 51 * happens, handle that and return -EFAULT. 52 */ 53 long __weak probe_kernel_write(void *dst, const void *src, size_t size) 54 __attribute__((alias("__probe_kernel_write"))); 55 56 long __probe_kernel_write(void *dst, const void *src, size_t size) 57 { 58 long ret; 59 mm_segment_t old_fs = get_fs(); 60 61 set_fs(KERNEL_DS); 62 pagefault_disable(); 63 current->kernel_uaccess_faults_ok++; 64 ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); 65 current->kernel_uaccess_faults_ok--; 66 pagefault_enable(); 67 set_fs(old_fs); 68 69 return ret ? -EFAULT : 0; 70 } 71 EXPORT_SYMBOL_GPL(probe_kernel_write); 72 73 /** 74 * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. 75 * @dst: Destination address, in kernel space. This buffer must be at 76 * least @count bytes long. 77 * @unsafe_addr: Unsafe address. 78 * @count: Maximum number of bytes to copy, including the trailing NUL. 79 * 80 * Copies a NUL-terminated string from unsafe address to kernel buffer. 81 * 82 * On success, returns the length of the string INCLUDING the trailing NUL. 83 * 84 * If access fails, returns -EFAULT (some data may have been copied 85 * and the trailing NUL added). 86 * 87 * If @count is smaller than the length of the string, copies @count-1 bytes, 88 * sets the last byte of @dst buffer to NUL and returns @count. 89 */ 90 long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) 91 { 92 mm_segment_t old_fs = get_fs(); 93 const void *src = unsafe_addr; 94 long ret; 95 96 if (unlikely(count <= 0)) 97 return 0; 98 99 set_fs(KERNEL_DS); 100 pagefault_disable(); 101 current->kernel_uaccess_faults_ok++; 102 103 do { 104 ret = __get_user(*dst++, (const char __user __force *)src++); 105 } while (dst[-1] && ret == 0 && src - unsafe_addr < count); 106 107 current->kernel_uaccess_faults_ok--; 108 dst[-1] = '\0'; 109 pagefault_enable(); 110 set_fs(old_fs); 111 112 return ret ? -EFAULT : src - unsafe_addr; 113 } 114