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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 #ifdef CONFIG_SET_FS
 14 /*
 15  * Force the uaccess routines to be wired up for actual userspace access,
 16  * overriding any possible set_fs(KERNEL_DS) still lingering around.  Undone
 17  * using force_uaccess_end below.
 18  */
 19 static inline mm_segment_t force_uaccess_begin(void)
 20 {
 21         mm_segment_t fs = get_fs();
 22 
 23         set_fs(USER_DS);
 24         return fs;
 25 }
 26 
 27 static inline void force_uaccess_end(mm_segment_t oldfs)
 28 {
 29         set_fs(oldfs);
 30 }
 31 #else /* CONFIG_SET_FS */
 32 typedef struct {
 33         /* empty dummy */
 34 } mm_segment_t;
 35 
 36 #ifndef TASK_SIZE_MAX
 37 #define TASK_SIZE_MAX                   TASK_SIZE
 38 #endif
 39 
 40 #define uaccess_kernel()                (false)
 41 #define user_addr_max()                 (TASK_SIZE_MAX)
 42 
 43 static inline mm_segment_t force_uaccess_begin(void)
 44 {
 45         return (mm_segment_t) { };
 46 }
 47 
 48 static inline void force_uaccess_end(mm_segment_t oldfs)
 49 {
 50 }
 51 #endif /* CONFIG_SET_FS */
 52 
 53 /*
 54  * Architectures should provide two primitives (raw_copy_{to,from}_user())
 55  * and get rid of their private instances of copy_{to,from}_user() and
 56  * __copy_{to,from}_user{,_inatomic}().
 57  *
 58  * raw_copy_{to,from}_user(to, from, size) should copy up to size bytes and
 59  * return the amount left to copy.  They should assume that access_ok() has
 60  * already been checked (and succeeded); they should *not* zero-pad anything.
 61  * No KASAN or object size checks either - those belong here.
 62  *
 63  * Both of these functions should attempt to copy size bytes starting at from
 64  * into the area starting at to.  They must not fetch or store anything
 65  * outside of those areas.  Return value must be between 0 (everything
 66  * copied successfully) and size (nothing copied).
 67  *
 68  * If raw_copy_{to,from}_user(to, from, size) returns N, size - N bytes starting
 69  * at to must become equal to the bytes fetched from the corresponding area
 70  * starting at from.  All data past to + size - N must be left unmodified.
 71  *
 72  * If copying succeeds, the return value must be 0.  If some data cannot be
 73  * fetched, it is permitted to copy less than had been fetched; the only
 74  * hard requirement is that not storing anything at all (i.e. returning size)
 75  * should happen only when nothing could be copied.  In other words, you don't
 76  * have to squeeze as much as possible - it is allowed, but not necessary.
 77  *
 78  * For raw_copy_from_user() to always points to kernel memory and no faults
 79  * on store should happen.  Interpretation of from is affected by set_fs().
 80  * For raw_copy_to_user() it's the other way round.
 81  *
 82  * Both can be inlined - it's up to architectures whether it wants to bother
 83  * with that.  They should not be used directly; they are used to implement
 84  * the 6 functions (copy_{to,from}_user(), __copy_{to,from}_user_inatomic())
 85  * that are used instead.  Out of those, __... ones are inlined.  Plain
 86  * copy_{to,from}_user() might or might not be inlined.  If you want them
 87  * inlined, have asm/uaccess.h define INLINE_COPY_{TO,FROM}_USER.
 88  *
 89  * NOTE: only copy_from_user() zero-pads the destination in case of short copy.
 90  * Neither __copy_from_user() nor __copy_from_user_inatomic() zero anything
 91  * at all; their callers absolutely must check the return value.
 92  *
 93  * Biarch ones should also provide raw_copy_in_user() - similar to the above,
 94  * but both source and destination are __user pointers (affected by set_fs()
 95  * as usual) and both source and destination can trigger faults.
 96  */
 97 
 98 static __always_inline __must_check unsigned long
 99 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
100 {
101         instrument_copy_from_user(to, from, n);
102         check_object_size(to, n, false);
103         return raw_copy_from_user(to, from, n);
104 }
105 
106 static __always_inline __must_check unsigned long
107 __copy_from_user(void *to, const void __user *from, unsigned long n)
108 {
109         might_fault();
110         if (should_fail_usercopy())
111                 return n;
112         instrument_copy_from_user(to, from, n);
113         check_object_size(to, n, false);
114         return raw_copy_from_user(to, from, n);
115 }
116 
117 /**
118  * __copy_to_user_inatomic: - Copy a block of data into user space, with less checking.
119  * @to:   Destination address, in user space.
120  * @from: Source address, in kernel space.
121  * @n:    Number of bytes to copy.
122  *
123  * Context: User context only.
124  *
125  * Copy data from kernel space to user space.  Caller must check
126  * the specified block with access_ok() before calling this function.
127  * The caller should also make sure he pins the user space address
128  * so that we don't result in page fault and sleep.
129  */
130 static __always_inline __must_check unsigned long
131 __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
132 {
133         if (should_fail_usercopy())
134                 return n;
135         instrument_copy_to_user(to, from, n);
136         check_object_size(from, n, true);
137         return raw_copy_to_user(to, from, n);
138 }
139 
140 static __always_inline __must_check unsigned long
141 __copy_to_user(void __user *to, const void *from, unsigned long n)
142 {
143         might_fault();
144         if (should_fail_usercopy())
145                 return n;
146         instrument_copy_to_user(to, from, n);
147         check_object_size(from, n, true);
148         return raw_copy_to_user(to, from, n);
149 }
150 
151 #ifdef INLINE_COPY_FROM_USER
152 static inline __must_check unsigned long
153 _copy_from_user(void *to, const void __user *from, unsigned long n)
154 {
155         unsigned long res = n;
156         might_fault();
157         if (!should_fail_usercopy() && likely(access_ok(from, n))) {
158                 instrument_copy_from_user(to, from, n);
159                 res = raw_copy_from_user(to, from, n);
160         }
161         if (unlikely(res))
162                 memset(to + (n - res), 0, res);
163         return res;
164 }
165 #else
166 extern __must_check unsigned long
167 _copy_from_user(void *, const void __user *, unsigned long);
168 #endif
169 
170 #ifdef INLINE_COPY_TO_USER
171 static inline __must_check unsigned long
172 _copy_to_user(void __user *to, const void *from, unsigned long n)
173 {
174         might_fault();
175         if (should_fail_usercopy())
176                 return n;
177         if (access_ok(to, n)) {
178                 instrument_copy_to_user(to, from, n);
179                 n = raw_copy_to_user(to, from, n);
180         }
181         return n;
182 }
183 #else
184 extern __must_check unsigned long
185 _copy_to_user(void __user *, const void *, unsigned long);
186 #endif
187 
188 static __always_inline unsigned long __must_check
189 copy_from_user(void *to, const void __user *from, unsigned long n)
190 {
191         if (likely(check_copy_size(to, n, false)))
192                 n = _copy_from_user(to, from, n);
193         return n;
194 }
195 
196 static __always_inline unsigned long __must_check
197 copy_to_user(void __user *to, const void *from, unsigned long n)
198 {
199         if (likely(check_copy_size(from, n, true)))
200                 n = _copy_to_user(to, from, n);
201         return n;
202 }
203 
204 #ifndef copy_mc_to_kernel
205 /*
206  * Without arch opt-in this generic copy_mc_to_kernel() will not handle
207  * #MC (or arch equivalent) during source read.
208  */
209 static inline unsigned long __must_check
210 copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
211 {
212         memcpy(dst, src, cnt);
213         return 0;
214 }
215 #endif
216 
217 static __always_inline void pagefault_disabled_inc(void)
218 {
219         current->pagefault_disabled++;
220 }
221 
222 static __always_inline void pagefault_disabled_dec(void)
223 {
224         current->pagefault_disabled--;
225 }
226 
227 /*
228  * These routines enable/disable the pagefault handler. If disabled, it will
229  * not take any locks and go straight to the fixup table.
230  *
231  * User access methods will not sleep when called from a pagefault_disabled()
232  * environment.
233  */
234 static inline void pagefault_disable(void)
235 {
236         pagefault_disabled_inc();
237         /*
238          * make sure to have issued the store before a pagefault
239          * can hit.
240          */
241         barrier();
242 }
243 
244 static inline void pagefault_enable(void)
245 {
246         /*
247          * make sure to issue those last loads/stores before enabling
248          * the pagefault handler again.
249          */
250         barrier();
251         pagefault_disabled_dec();
252 }
253 
254 /*
255  * Is the pagefault handler disabled? If so, user access methods will not sleep.
256  */
257 static inline bool pagefault_disabled(void)
258 {
259         return current->pagefault_disabled != 0;
260 }
261 
262 /*
263  * The pagefault handler is in general disabled by pagefault_disable() or
264  * when in irq context (via in_atomic()).
265  *
266  * This function should only be used by the fault handlers. Other users should
267  * stick to pagefault_disabled().
268  * Please NEVER use preempt_disable() to disable the fault handler. With
269  * !CONFIG_PREEMPT_COUNT, this is like a NOP. So the handler won't be disabled.
270  * in_atomic() will report different values based on !CONFIG_PREEMPT_COUNT.
271  */
272 #define faulthandler_disabled() (pagefault_disabled() || in_atomic())
273 
274 #ifndef ARCH_HAS_NOCACHE_UACCESS
275 
276 static inline __must_check unsigned long
277 __copy_from_user_inatomic_nocache(void *to, const void __user *from,
278                                   unsigned long n)
279 {
280         return __copy_from_user_inatomic(to, from, n);
281 }
282 
283 #endif          /* ARCH_HAS_NOCACHE_UACCESS */
284 
285 extern __must_check int check_zeroed_user(const void __user *from, size_t size);
286 
287 /**
288  * copy_struct_from_user: copy a struct from userspace
289  * @dst:   Destination address, in kernel space. This buffer must be @ksize
290  *         bytes long.
291  * @ksize: Size of @dst struct.
292  * @src:   Source address, in userspace.
293  * @usize: (Alleged) size of @src struct.
294  *
295  * Copies a struct from userspace to kernel space, in a way that guarantees
296  * backwards-compatibility for struct syscall arguments (as long as future
297  * struct extensions are made such that all new fields are *appended* to the
298  * old struct, and zeroed-out new fields have the same meaning as the old
299  * struct).
300  *
301  * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
302  * The recommended usage is something like the following:
303  *
304  *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
305  *   {
306  *      int err;
307  *      struct foo karg = {};
308  *
309  *      if (usize > PAGE_SIZE)
310  *        return -E2BIG;
311  *      if (usize < FOO_SIZE_VER0)
312  *        return -EINVAL;
313  *
314  *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, usize);
315  *      if (err)
316  *        return err;
317  *
318  *      // ...
319  *   }
320  *
321  * There are three cases to consider:
322  *  * If @usize == @ksize, then it's copied verbatim.
323  *  * If @usize < @ksize, then the userspace has passed an old struct to a
324  *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
325  *    are to be zero-filled.
326  *  * If @usize > @ksize, then the userspace has passed a new struct to an
327  *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
328  *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
329  *
330  * Returns (in all cases, some data may have been copied):
331  *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
332  *  * -EFAULT: access to userspace failed.
333  */
334 static __always_inline __must_check int
335 copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
336                       size_t usize)
337 {
338         size_t size = min(ksize, usize);
339         size_t rest = max(ksize, usize) - size;
340 
341         /* Deal with trailing bytes. */
342         if (usize < ksize) {
343                 memset(dst + size, 0, rest);
344         } else if (usize > ksize) {
345                 int ret = check_zeroed_user(src + size, rest);
346                 if (ret <= 0)
347                         return ret ?: -E2BIG;
348         }
349         /* Copy the interoperable parts of the struct. */
350         if (copy_from_user(dst, src, size))
351                 return -EFAULT;
352         return 0;
353 }
354 
355 bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size);
356 
357 long copy_from_kernel_nofault(void *dst, const void *src, size_t size);
358 long notrace copy_to_kernel_nofault(void *dst, const void *src, size_t size);
359 
360 long copy_from_user_nofault(void *dst, const void __user *src, size_t size);
361 long notrace copy_to_user_nofault(void __user *dst, const void *src,
362                 size_t size);
363 
364 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr,
365                 long count);
366 
367 long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
368                 long count);
369 long strnlen_user_nofault(const void __user *unsafe_addr, long count);
370 
371 /**
372  * get_kernel_nofault(): safely attempt to read from a location
373  * @val: read into this variable
374  * @ptr: address to read from
375  *
376  * Returns 0 on success, or -EFAULT.
377  */
378 #define get_kernel_nofault(val, ptr) ({                         \
379         const typeof(val) *__gk_ptr = (ptr);                    \
380         copy_from_kernel_nofault(&(val), __gk_ptr, sizeof(val));\
381 })
382 
383 #ifndef user_access_begin
384 #define user_access_begin(ptr,len) access_ok(ptr, len)
385 #define user_access_end() do { } while (0)
386 #define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
387 #define unsafe_get_user(x,p,e) unsafe_op_wrap(__get_user(x,p),e)
388 #define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user(x,p),e)
389 #define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(__copy_to_user(d,s,l),e)
390 #define unsafe_copy_from_user(d,s,l,e) unsafe_op_wrap(__copy_from_user(d,s,l),e)
391 static inline unsigned long user_access_save(void) { return 0UL; }
392 static inline void user_access_restore(unsigned long flags) { }
393 #endif
394 #ifndef user_write_access_begin
395 #define user_write_access_begin user_access_begin
396 #define user_write_access_end user_access_end
397 #endif
398 #ifndef user_read_access_begin
399 #define user_read_access_begin user_access_begin
400 #define user_read_access_end user_access_end
401 #endif
402 
403 #ifdef CONFIG_HARDENED_USERCOPY
404 void usercopy_warn(const char *name, const char *detail, bool to_user,
405                    unsigned long offset, unsigned long len);
406 void __noreturn usercopy_abort(const char *name, const char *detail,
407                                bool to_user, unsigned long offset,
408                                unsigned long len);
409 #endif
410 
411 #endif          /* __LINUX_UACCESS_H__ */
412 

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