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Linux/arch/x86/kernel/fpu/signal.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * FPU signal frame handling routines.
  4  */
  5 
  6 #include <linux/compat.h>
  7 #include <linux/cpu.h>
  8 #include <linux/pagemap.h>
  9 
 10 #include <asm/fpu/internal.h>
 11 #include <asm/fpu/signal.h>
 12 #include <asm/fpu/regset.h>
 13 #include <asm/fpu/xstate.h>
 14 
 15 #include <asm/sigframe.h>
 16 #include <asm/trace/fpu.h>
 17 
 18 static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
 19 
 20 /*
 21  * Check for the presence of extended state information in the
 22  * user fpstate pointer in the sigcontext.
 23  */
 24 static inline int check_for_xstate(struct fxregs_state __user *buf,
 25                                    void __user *fpstate,
 26                                    struct _fpx_sw_bytes *fx_sw)
 27 {
 28         int min_xstate_size = sizeof(struct fxregs_state) +
 29                               sizeof(struct xstate_header);
 30         unsigned int magic2;
 31 
 32         if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
 33                 return -1;
 34 
 35         /* Check for the first magic field and other error scenarios. */
 36         if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
 37             fx_sw->xstate_size < min_xstate_size ||
 38             fx_sw->xstate_size > fpu_user_xstate_size ||
 39             fx_sw->xstate_size > fx_sw->extended_size)
 40                 return -1;
 41 
 42         /*
 43          * Check for the presence of second magic word at the end of memory
 44          * layout. This detects the case where the user just copied the legacy
 45          * fpstate layout with out copying the extended state information
 46          * in the memory layout.
 47          */
 48         if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
 49             || magic2 != FP_XSTATE_MAGIC2)
 50                 return -1;
 51 
 52         return 0;
 53 }
 54 
 55 /*
 56  * Signal frame handlers.
 57  */
 58 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
 59 {
 60         if (use_fxsr()) {
 61                 struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
 62                 struct user_i387_ia32_struct env;
 63                 struct _fpstate_32 __user *fp = buf;
 64 
 65                 fpregs_lock();
 66                 if (!test_thread_flag(TIF_NEED_FPU_LOAD))
 67                         copy_fxregs_to_kernel(&tsk->thread.fpu);
 68                 fpregs_unlock();
 69 
 70                 convert_from_fxsr(&env, tsk);
 71 
 72                 if (__copy_to_user(buf, &env, sizeof(env)) ||
 73                     __put_user(xsave->i387.swd, &fp->status) ||
 74                     __put_user(X86_FXSR_MAGIC, &fp->magic))
 75                         return -1;
 76         } else {
 77                 struct fregs_state __user *fp = buf;
 78                 u32 swd;
 79                 if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
 80                         return -1;
 81         }
 82 
 83         return 0;
 84 }
 85 
 86 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
 87 {
 88         struct xregs_state __user *x = buf;
 89         struct _fpx_sw_bytes *sw_bytes;
 90         u32 xfeatures;
 91         int err;
 92 
 93         /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
 94         sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
 95         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
 96 
 97         if (!use_xsave())
 98                 return err;
 99 
100         err |= __put_user(FP_XSTATE_MAGIC2,
101                           (__u32 __user *)(buf + fpu_user_xstate_size));
102 
103         /*
104          * Read the xfeatures which we copied (directly from the cpu or
105          * from the state in task struct) to the user buffers.
106          */
107         err |= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
108 
109         /*
110          * For legacy compatible, we always set FP/SSE bits in the bit
111          * vector while saving the state to the user context. This will
112          * enable us capturing any changes(during sigreturn) to
113          * the FP/SSE bits by the legacy applications which don't touch
114          * xfeatures in the xsave header.
115          *
116          * xsave aware apps can change the xfeatures in the xsave
117          * header as well as change any contents in the memory layout.
118          * xrestore as part of sigreturn will capture all the changes.
119          */
120         xfeatures |= XFEATURE_MASK_FPSSE;
121 
122         err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
123 
124         return err;
125 }
126 
127 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
128 {
129         int err;
130 
131         if (use_xsave())
132                 err = copy_xregs_to_user(buf);
133         else if (use_fxsr())
134                 err = copy_fxregs_to_user((struct fxregs_state __user *) buf);
135         else
136                 err = copy_fregs_to_user((struct fregs_state __user *) buf);
137 
138         if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
139                 err = -EFAULT;
140         return err;
141 }
142 
143 /*
144  * Save the fpu, extended register state to the user signal frame.
145  *
146  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
147  *  state is copied.
148  *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
149  *
150  *      buf == buf_fx for 64-bit frames and 32-bit fsave frame.
151  *      buf != buf_fx for 32-bit frames with fxstate.
152  *
153  * Try to save it directly to the user frame with disabled page fault handler.
154  * If this fails then do the slow path where the FPU state is first saved to
155  * task's fpu->state and then copy it to the user frame pointed to by the
156  * aligned pointer 'buf_fx'.
157  *
158  * If this is a 32-bit frame with fxstate, put a fsave header before
159  * the aligned state at 'buf_fx'.
160  *
161  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
162  * indicating the absence/presence of the extended state to the user.
163  */
164 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
165 {
166         struct task_struct *tsk = current;
167         int ia32_fxstate = (buf != buf_fx);
168         int ret;
169 
170         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
171                          IS_ENABLED(CONFIG_IA32_EMULATION));
172 
173         if (!access_ok(buf, size))
174                 return -EACCES;
175 
176         if (!static_cpu_has(X86_FEATURE_FPU))
177                 return fpregs_soft_get(current, NULL, 0,
178                         sizeof(struct user_i387_ia32_struct), NULL,
179                         (struct _fpstate_32 __user *) buf) ? -1 : 1;
180 
181 retry:
182         /*
183          * Load the FPU registers if they are not valid for the current task.
184          * With a valid FPU state we can attempt to save the state directly to
185          * userland's stack frame which will likely succeed. If it does not,
186          * resolve the fault in the user memory and try again.
187          */
188         fpregs_lock();
189         if (test_thread_flag(TIF_NEED_FPU_LOAD))
190                 __fpregs_load_activate();
191 
192         pagefault_disable();
193         ret = copy_fpregs_to_sigframe(buf_fx);
194         pagefault_enable();
195         fpregs_unlock();
196 
197         if (ret) {
198                 if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
199                         goto retry;
200                 return -EFAULT;
201         }
202 
203         /* Save the fsave header for the 32-bit frames. */
204         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
205                 return -1;
206 
207         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
208                 return -1;
209 
210         return 0;
211 }
212 
213 static inline void
214 sanitize_restored_xstate(union fpregs_state *state,
215                          struct user_i387_ia32_struct *ia32_env,
216                          u64 xfeatures, int fx_only)
217 {
218         struct xregs_state *xsave = &state->xsave;
219         struct xstate_header *header = &xsave->header;
220 
221         if (use_xsave()) {
222                 /*
223                  * Note: we don't need to zero the reserved bits in the
224                  * xstate_header here because we either didn't copy them at all,
225                  * or we checked earlier that they aren't set.
226                  */
227 
228                 /*
229                  * Init the state that is not present in the memory
230                  * layout and not enabled by the OS.
231                  */
232                 if (fx_only)
233                         header->xfeatures = XFEATURE_MASK_FPSSE;
234                 else
235                         header->xfeatures &= xfeatures;
236         }
237 
238         if (use_fxsr()) {
239                 /*
240                  * mscsr reserved bits must be masked to zero for security
241                  * reasons.
242                  */
243                 xsave->i387.mxcsr &= mxcsr_feature_mask;
244 
245                 if (ia32_env)
246                         convert_to_fxsr(&state->fxsave, ia32_env);
247         }
248 }
249 
250 /*
251  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
252  */
253 static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
254 {
255         if (use_xsave()) {
256                 if (fx_only) {
257                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
258                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
259                         return copy_user_to_fxregs(buf);
260                 } else {
261                         u64 init_bv = xfeatures_mask & ~xbv;
262                         if (unlikely(init_bv))
263                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
264                         return copy_user_to_xregs(buf, xbv);
265                 }
266         } else if (use_fxsr()) {
267                 return copy_user_to_fxregs(buf);
268         } else
269                 return copy_user_to_fregs(buf);
270 }
271 
272 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
273 {
274         struct user_i387_ia32_struct *envp = NULL;
275         int state_size = fpu_kernel_xstate_size;
276         int ia32_fxstate = (buf != buf_fx);
277         struct task_struct *tsk = current;
278         struct fpu *fpu = &tsk->thread.fpu;
279         struct user_i387_ia32_struct env;
280         u64 xfeatures = 0;
281         int fx_only = 0;
282         int ret = 0;
283 
284         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
285                          IS_ENABLED(CONFIG_IA32_EMULATION));
286 
287         if (!buf) {
288                 fpu__clear(fpu);
289                 return 0;
290         }
291 
292         if (!access_ok(buf, size))
293                 return -EACCES;
294 
295         if (!static_cpu_has(X86_FEATURE_FPU))
296                 return fpregs_soft_set(current, NULL,
297                                        0, sizeof(struct user_i387_ia32_struct),
298                                        NULL, buf) != 0;
299 
300         if (use_xsave()) {
301                 struct _fpx_sw_bytes fx_sw_user;
302                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
303                         /*
304                          * Couldn't find the extended state information in the
305                          * memory layout. Restore just the FP/SSE and init all
306                          * the other extended state.
307                          */
308                         state_size = sizeof(struct fxregs_state);
309                         fx_only = 1;
310                         trace_x86_fpu_xstate_check_failed(fpu);
311                 } else {
312                         state_size = fx_sw_user.xstate_size;
313                         xfeatures = fx_sw_user.xfeatures;
314                 }
315         }
316 
317         /*
318          * The current state of the FPU registers does not matter. By setting
319          * TIF_NEED_FPU_LOAD unconditionally it is ensured that the our xstate
320          * is not modified on context switch and that the xstate is considered
321          * to be loaded again on return to userland (overriding last_cpu avoids
322          * the optimisation).
323          */
324         set_thread_flag(TIF_NEED_FPU_LOAD);
325         __fpu_invalidate_fpregs_state(fpu);
326 
327         if ((unsigned long)buf_fx % 64)
328                 fx_only = 1;
329         /*
330          * For 32-bit frames with fxstate, copy the fxstate so it can be
331          * reconstructed later.
332          */
333         if (ia32_fxstate) {
334                 ret = __copy_from_user(&env, buf, sizeof(env));
335                 if (ret)
336                         goto err_out;
337                 envp = &env;
338         } else {
339                 /*
340                  * Attempt to restore the FPU registers directly from user
341                  * memory. For that to succeed, the user access cannot cause
342                  * page faults. If it does, fall back to the slow path below,
343                  * going through the kernel buffer with the enabled pagefault
344                  * handler.
345                  */
346                 fpregs_lock();
347                 pagefault_disable();
348                 ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
349                 pagefault_enable();
350                 if (!ret) {
351                         fpregs_mark_activate();
352                         fpregs_unlock();
353                         return 0;
354                 }
355                 fpregs_unlock();
356         }
357 
358 
359         if (use_xsave() && !fx_only) {
360                 u64 init_bv = xfeatures_mask & ~xfeatures;
361 
362                 if (using_compacted_format()) {
363                         ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
364                 } else {
365                         ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
366 
367                         if (!ret && state_size > offsetof(struct xregs_state, header))
368                                 ret = validate_xstate_header(&fpu->state.xsave.header);
369                 }
370                 if (ret)
371                         goto err_out;
372 
373                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
374 
375                 fpregs_lock();
376                 if (unlikely(init_bv))
377                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
378                 ret = copy_kernel_to_xregs_err(&fpu->state.xsave, xfeatures);
379 
380         } else if (use_fxsr()) {
381                 ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
382                 if (ret) {
383                         ret = -EFAULT;
384                         goto err_out;
385                 }
386 
387                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
388 
389                 fpregs_lock();
390                 if (use_xsave()) {
391                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
392                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
393                 }
394 
395                 ret = copy_kernel_to_fxregs_err(&fpu->state.fxsave);
396         } else {
397                 ret = __copy_from_user(&fpu->state.fsave, buf_fx, state_size);
398                 if (ret)
399                         goto err_out;
400 
401                 fpregs_lock();
402                 ret = copy_kernel_to_fregs_err(&fpu->state.fsave);
403         }
404         if (!ret)
405                 fpregs_mark_activate();
406         fpregs_unlock();
407 
408 err_out:
409         if (ret)
410                 fpu__clear(fpu);
411         return ret;
412 }
413 
414 static inline int xstate_sigframe_size(void)
415 {
416         return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
417                         fpu_user_xstate_size;
418 }
419 
420 /*
421  * Restore FPU state from a sigframe:
422  */
423 int fpu__restore_sig(void __user *buf, int ia32_frame)
424 {
425         void __user *buf_fx = buf;
426         int size = xstate_sigframe_size();
427 
428         if (ia32_frame && use_fxsr()) {
429                 buf_fx = buf + sizeof(struct fregs_state);
430                 size += sizeof(struct fregs_state);
431         }
432 
433         return __fpu__restore_sig(buf, buf_fx, size);
434 }
435 
436 unsigned long
437 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
438                      unsigned long *buf_fx, unsigned long *size)
439 {
440         unsigned long frame_size = xstate_sigframe_size();
441 
442         *buf_fx = sp = round_down(sp - frame_size, 64);
443         if (ia32_frame && use_fxsr()) {
444                 frame_size += sizeof(struct fregs_state);
445                 sp -= sizeof(struct fregs_state);
446         }
447 
448         *size = frame_size;
449 
450         return sp;
451 }
452 /*
453  * Prepare the SW reserved portion of the fxsave memory layout, indicating
454  * the presence of the extended state information in the memory layout
455  * pointed by the fpstate pointer in the sigcontext.
456  * This will be saved when ever the FP and extended state context is
457  * saved on the user stack during the signal handler delivery to the user.
458  */
459 void fpu__init_prepare_fx_sw_frame(void)
460 {
461         int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
462 
463         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
464         fx_sw_reserved.extended_size = size;
465         fx_sw_reserved.xfeatures = xfeatures_mask;
466         fx_sw_reserved.xstate_size = fpu_user_xstate_size;
467 
468         if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
469             IS_ENABLED(CONFIG_X86_32)) {
470                 int fsave_header_size = sizeof(struct fregs_state);
471 
472                 fx_sw_reserved_ia32 = fx_sw_reserved;
473                 fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
474         }
475 }
476 
477 

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