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TOMOYO Linux Cross Reference
Linux/include/linux/uaccess.h

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 #ifndef __LINUX_UACCESS_H__
  3 #define __LINUX_UACCESS_H__
  4 
  5 #include <linux/fault-inject-usercopy.h>
  6 #include <linux/instrumented.h>
  7 #include <linux/minmax.h>
  8 #include <linux/sched.h>
  9 #include <linux/thread_info.h>
 10 
 11 #include <asm/uaccess.h>
 12 
 13 /*
 14  * Architectures should provide two primitives (raw_copy_{to,from}_user())
 15  * and get rid of their private instances of copy_{to,from}_user() and
 16  * __copy_{to,from}_user{,_inatomic}().
 17  *
 18  * raw_copy_{to,from}_user(to, from, size) should copy up to size bytes and
 19  * return the amount left to copy.  They should assume that access_ok() has
 20  * already been checked (and succeeded); they should *not* zero-pad anything.
 21  * No KASAN or object size checks either - those belong here.
 22  *
 23  * Both of these functions should attempt to copy size bytes starting at from
 24  * into the area starting at to.  They must not fetch or store anything
 25  * outside of those areas.  Return value must be between 0 (everything
 26  * copied successfully) and size (nothing copied).
 27  *
 28  * If raw_copy_{to,from}_user(to, from, size) returns N, size - N bytes starting
 29  * at to must become equal to the bytes fetched from the corresponding area
 30  * starting at from.  All data past to + size - N must be left unmodified.
 31  *
 32  * If copying succeeds, the return value must be 0.  If some data cannot be
 33  * fetched, it is permitted to copy less than had been fetched; the only
 34  * hard requirement is that not storing anything at all (i.e. returning size)
 35  * should happen only when nothing could be copied.  In other words, you don't
 36  * have to squeeze as much as possible - it is allowed, but not necessary.
 37  *
 38  * For raw_copy_from_user() to always points to kernel memory and no faults
 39  * on store should happen.  Interpretation of from is affected by set_fs().
 40  * For raw_copy_to_user() it's the other way round.
 41  *
 42  * Both can be inlined - it's up to architectures whether it wants to bother
 43  * with that.  They should not be used directly; they are used to implement
 44  * the 6 functions (copy_{to,from}_user(), __copy_{to,from}_user_inatomic())
 45  * that are used instead.  Out of those, __... ones are inlined.  Plain
 46  * copy_{to,from}_user() might or might not be inlined.  If you want them
 47  * inlined, have asm/uaccess.h define INLINE_COPY_{TO,FROM}_USER.
 48  *
 49  * NOTE: only copy_from_user() zero-pads the destination in case of short copy.
 50  * Neither __copy_from_user() nor __copy_from_user_inatomic() zero anything
 51  * at all; their callers absolutely must check the return value.
 52  *
 53  * Biarch ones should also provide raw_copy_in_user() - similar to the above,
 54  * but both source and destination are __user pointers (affected by set_fs()
 55  * as usual) and both source and destination can trigger faults.
 56  */
 57 
 58 static __always_inline __must_check unsigned long
 59 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 60 {
 61         instrument_copy_from_user(to, from, n);
 62         check_object_size(to, n, false);
 63         return raw_copy_from_user(to, from, n);
 64 }
 65 
 66 static __always_inline __must_check unsigned long
 67 __copy_from_user(void *to, const void __user *from, unsigned long n)
 68 {
 69         might_fault();
 70         if (should_fail_usercopy())
 71                 return n;
 72         instrument_copy_from_user(to, from, n);
 73         check_object_size(to, n, false);
 74         return raw_copy_from_user(to, from, n);
 75 }
 76 
 77 /**
 78  * __copy_to_user_inatomic: - Copy a block of data into user space, with less checking.
 79  * @to:   Destination address, in user space.
 80  * @from: Source address, in kernel space.
 81  * @n:    Number of bytes to copy.
 82  *
 83  * Context: User context only.
 84  *
 85  * Copy data from kernel space to user space.  Caller must check
 86  * the specified block with access_ok() before calling this function.
 87  * The caller should also make sure he pins the user space address
 88  * so that we don't result in page fault and sleep.
 89  */
 90 static __always_inline __must_check unsigned long
 91 __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
 92 {
 93         if (should_fail_usercopy())
 94                 return n;
 95         instrument_copy_to_user(to, from, n);
 96         check_object_size(from, n, true);
 97         return raw_copy_to_user(to, from, n);
 98 }
 99 
100 static __always_inline __must_check unsigned long
101 __copy_to_user(void __user *to, const void *from, unsigned long n)
102 {
103         might_fault();
104         if (should_fail_usercopy())
105                 return n;
106         instrument_copy_to_user(to, from, n);
107         check_object_size(from, n, true);
108         return raw_copy_to_user(to, from, n);
109 }
110 
111 #ifdef INLINE_COPY_FROM_USER
112 static inline __must_check unsigned long
113 _copy_from_user(void *to, const void __user *from, unsigned long n)
114 {
115         unsigned long res = n;
116         might_fault();
117         if (!should_fail_usercopy() && likely(access_ok(from, n))) {
118                 instrument_copy_from_user(to, from, n);
119                 res = raw_copy_from_user(to, from, n);
120         }
121         if (unlikely(res))
122                 memset(to + (n - res), 0, res);
123         return res;
124 }
125 #else
126 extern __must_check unsigned long
127 _copy_from_user(void *, const void __user *, unsigned long);
128 #endif
129 
130 #ifdef INLINE_COPY_TO_USER
131 static inline __must_check unsigned long
132 _copy_to_user(void __user *to, const void *from, unsigned long n)
133 {
134         might_fault();
135         if (should_fail_usercopy())
136                 return n;
137         if (access_ok(to, n)) {
138                 instrument_copy_to_user(to, from, n);
139                 n = raw_copy_to_user(to, from, n);
140         }
141         return n;
142 }
143 #else
144 extern __must_check unsigned long
145 _copy_to_user(void __user *, const void *, unsigned long);
146 #endif
147 
148 static __always_inline unsigned long __must_check
149 copy_from_user(void *to, const void __user *from, unsigned long n)
150 {
151         if (likely(check_copy_size(to, n, false)))
152                 n = _copy_from_user(to, from, n);
153         return n;
154 }
155 
156 static __always_inline unsigned long __must_check
157 copy_to_user(void __user *to, const void *from, unsigned long n)
158 {
159         if (likely(check_copy_size(from, n, true)))
160                 n = _copy_to_user(to, from, n);
161         return n;
162 }
163 
164 #ifndef copy_mc_to_kernel
165 /*
166  * Without arch opt-in this generic copy_mc_to_kernel() will not handle
167  * #MC (or arch equivalent) during source read.
168  */
169 static inline unsigned long __must_check
170 copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
171 {
172         memcpy(dst, src, cnt);
173         return 0;
174 }
175 #endif
176 
177 static __always_inline void pagefault_disabled_inc(void)
178 {
179         current->pagefault_disabled++;
180 }
181 
182 static __always_inline void pagefault_disabled_dec(void)
183 {
184         current->pagefault_disabled--;
185 }
186 
187 /*
188  * These routines enable/disable the pagefault handler. If disabled, it will
189  * not take any locks and go straight to the fixup table.
190  *
191  * User access methods will not sleep when called from a pagefault_disabled()
192  * environment.
193  */
194 static inline void pagefault_disable(void)
195 {
196         pagefault_disabled_inc();
197         /*
198          * make sure to have issued the store before a pagefault
199          * can hit.
200          */
201         barrier();
202 }
203 
204 static inline void pagefault_enable(void)
205 {
206         /*
207          * make sure to issue those last loads/stores before enabling
208          * the pagefault handler again.
209          */
210         barrier();
211         pagefault_disabled_dec();
212 }
213 
214 /*
215  * Is the pagefault handler disabled? If so, user access methods will not sleep.
216  */
217 static inline bool pagefault_disabled(void)
218 {
219         return current->pagefault_disabled != 0;
220 }
221 
222 /*
223  * The pagefault handler is in general disabled by pagefault_disable() or
224  * when in irq context (via in_atomic()).
225  *
226  * This function should only be used by the fault handlers. Other users should
227  * stick to pagefault_disabled().
228  * Please NEVER use preempt_disable() to disable the fault handler. With
229  * !CONFIG_PREEMPT_COUNT, this is like a NOP. So the handler won't be disabled.
230  * in_atomic() will report different values based on !CONFIG_PREEMPT_COUNT.
231  */
232 #define faulthandler_disabled() (pagefault_disabled() || in_atomic())
233 
234 #ifndef CONFIG_ARCH_HAS_SUBPAGE_FAULTS
235 
236 /**
237  * probe_subpage_writeable: probe the user range for write faults at sub-page
238  *                          granularity (e.g. arm64 MTE)
239  * @uaddr: start of address range
240  * @size: size of address range
241  *
242  * Returns 0 on success, the number of bytes not probed on fault.
243  *
244  * It is expected that the caller checked for the write permission of each
245  * page in the range either by put_user() or GUP. The architecture port can
246  * implement a more efficient get_user() probing if the same sub-page faults
247  * are triggered by either a read or a write.
248  */
249 static inline size_t probe_subpage_writeable(char __user *uaddr, size_t size)
250 {
251         return 0;
252 }
253 
254 #endif /* CONFIG_ARCH_HAS_SUBPAGE_FAULTS */
255 
256 #ifndef ARCH_HAS_NOCACHE_UACCESS
257 
258 static inline __must_check unsigned long
259 __copy_from_user_inatomic_nocache(void *to, const void __user *from,
260                                   unsigned long n)
261 {
262         return __copy_from_user_inatomic(to, from, n);
263 }
264 
265 #endif          /* ARCH_HAS_NOCACHE_UACCESS */
266 
267 extern __must_check int check_zeroed_user(const void __user *from, size_t size);
268 
269 /**
270  * copy_struct_from_user: copy a struct from userspace
271  * @dst:   Destination address, in kernel space. This buffer must be @ksize
272  *         bytes long.
273  * @ksize: Size of @dst struct.
274  * @src:   Source address, in userspace.
275  * @usize: (Alleged) size of @src struct.
276  *
277  * Copies a struct from userspace to kernel space, in a way that guarantees
278  * backwards-compatibility for struct syscall arguments (as long as future
279  * struct extensions are made such that all new fields are *appended* to the
280  * old struct, and zeroed-out new fields have the same meaning as the old
281  * struct).
282  *
283  * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
284  * The recommended usage is something like the following:
285  *
286  *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
287  *   {
288  *      int err;
289  *      struct foo karg = {};
290  *
291  *      if (usize > PAGE_SIZE)
292  *        return -E2BIG;
293  *      if (usize < FOO_SIZE_VER0)
294  *        return -EINVAL;
295  *
296  *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, usize);
297  *      if (err)
298  *        return err;
299  *
300  *      // ...
301  *   }
302  *
303  * There are three cases to consider:
304  *  * If @usize == @ksize, then it's copied verbatim.
305  *  * If @usize < @ksize, then the userspace has passed an old struct to a
306  *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
307  *    are to be zero-filled.
308  *  * If @usize > @ksize, then the userspace has passed a new struct to an
309  *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
310  *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
311  *
312  * Returns (in all cases, some data may have been copied):
313  *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
314  *  * -EFAULT: access to userspace failed.
315  */
316 static __always_inline __must_check int
317 copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
318                       size_t usize)
319 {
320         size_t size = min(ksize, usize);
321         size_t rest = max(ksize, usize) - size;
322 
323         /* Deal with trailing bytes. */
324         if (usize < ksize) {
325                 memset(dst + size, 0, rest);
326         } else if (usize > ksize) {
327                 int ret = check_zeroed_user(src + size, rest);
328                 if (ret <= 0)
329                         return ret ?: -E2BIG;
330         }
331         /* Copy the interoperable parts of the struct. */
332         if (copy_from_user(dst, src, size))
333                 return -EFAULT;
334         return 0;
335 }
336 
337 bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size);
338 
339 long copy_from_kernel_nofault(void *dst, const void *src, size_t size);
340 long notrace copy_to_kernel_nofault(void *dst, const void *src, size_t size);
341 
342 long copy_from_user_nofault(void *dst, const void __user *src, size_t size);
343 long notrace copy_to_user_nofault(void __user *dst, const void *src,
344                 size_t size);
345 
346 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr,
347                 long count);
348 
349 long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
350                 long count);
351 long strnlen_user_nofault(const void __user *unsafe_addr, long count);
352 
353 #ifndef __get_kernel_nofault
354 #define __get_kernel_nofault(dst, src, type, label)     \
355 do {                                                    \
356         type __user *p = (type __force __user *)(src);  \
357         type data;                                      \
358         if (__get_user(data, p))                        \
359                 goto label;                             \
360         *(type *)dst = data;                            \
361 } while (0)
362 
363 #define __put_kernel_nofault(dst, src, type, label)     \
364 do {                                                    \
365         type __user *p = (type __force __user *)(dst);  \
366         type data = *(type *)src;                       \
367         if (__put_user(data, p))                        \
368                 goto label;                             \
369 } while (0)
370 #endif
371 
372 /**
373  * get_kernel_nofault(): safely attempt to read from a location
374  * @val: read into this variable
375  * @ptr: address to read from
376  *
377  * Returns 0 on success, or -EFAULT.
378  */
379 #define get_kernel_nofault(val, ptr) ({                         \
380         const typeof(val) *__gk_ptr = (ptr);                    \
381         copy_from_kernel_nofault(&(val), __gk_ptr, sizeof(val));\
382 })
383 
384 #ifndef user_access_begin
385 #define user_access_begin(ptr,len) access_ok(ptr, len)
386 #define user_access_end() do { } while (0)
387 #define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
388 #define unsafe_get_user(x,p,e) unsafe_op_wrap(__get_user(x,p),e)
389 #define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user(x,p),e)
390 #define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(__copy_to_user(d,s,l),e)
391 #define unsafe_copy_from_user(d,s,l,e) unsafe_op_wrap(__copy_from_user(d,s,l),e)
392 static inline unsigned long user_access_save(void) { return 0UL; }
393 static inline void user_access_restore(unsigned long flags) { }
394 #endif
395 #ifndef user_write_access_begin
396 #define user_write_access_begin user_access_begin
397 #define user_write_access_end user_access_end
398 #endif
399 #ifndef user_read_access_begin
400 #define user_read_access_begin user_access_begin
401 #define user_read_access_end user_access_end
402 #endif
403 
404 #ifdef CONFIG_HARDENED_USERCOPY
405 void __noreturn usercopy_abort(const char *name, const char *detail,
406                                bool to_user, unsigned long offset,
407                                unsigned long len);
408 #endif
409 
410 #endif          /* __LINUX_UACCESS_H__ */
411 

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