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xsave.c
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1 /*
2  * xsave/xrstor support.
3  *
4  * Author: Suresh Siddha <[email protected]>
5  */
6 
7 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
8 
9 #include <linux/bootmem.h>
10 #include <linux/compat.h>
11 #include <asm/i387.h>
12 #include <asm/fpu-internal.h>
13 #include <asm/sigframe.h>
14 #include <asm/xcr.h>
15 
16 /*
17  * Supported feature mask by the CPU and the kernel.
18  */
20 
21 /*
22  * Represents init state for the supported extended state.
23  */
25 
26 static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
27 static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
28 
29 /*
30  * If a processor implementation discern that a processor state component is
31  * in its initialized state it may modify the corresponding bit in the
32  * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
33  * layout in the case of xsaveopt. While presenting the xstate information to
34  * the user, we always ensure that the memory layout of a feature will be in
35  * the init state if the corresponding header bit is zero. This is to ensure
36  * that the user doesn't see some stale state in the memory layout during
37  * signal handling, debugging etc.
38  */
40 {
41  struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
42  int feature_bit = 0x2;
43  u64 xstate_bv;
44 
45  if (!fx)
46  return;
47 
48  xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
49 
50  /*
51  * None of the feature bits are in init state. So nothing else
52  * to do for us, as the memory layout is up to date.
53  */
54  if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
55  return;
56 
57  /*
58  * FP is in init state
59  */
60  if (!(xstate_bv & XSTATE_FP)) {
61  fx->cwd = 0x37f;
62  fx->swd = 0;
63  fx->twd = 0;
64  fx->fop = 0;
65  fx->rip = 0;
66  fx->rdp = 0;
67  memset(&fx->st_space[0], 0, 128);
68  }
69 
70  /*
71  * SSE is in init state
72  */
73  if (!(xstate_bv & XSTATE_SSE))
74  memset(&fx->xmm_space[0], 0, 256);
75 
76  xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
77 
78  /*
79  * Update all the other memory layouts for which the corresponding
80  * header bit is in the init state.
81  */
82  while (xstate_bv) {
83  if (xstate_bv & 0x1) {
84  int offset = xstate_offsets[feature_bit];
85  int size = xstate_sizes[feature_bit];
86 
87  memcpy(((void *) fx) + offset,
88  ((void *) init_xstate_buf) + offset,
89  size);
90  }
91 
92  xstate_bv >>= 1;
93  feature_bit++;
94  }
95 }
96 
97 /*
98  * Check for the presence of extended state information in the
99  * user fpstate pointer in the sigcontext.
100  */
101 static inline int check_for_xstate(struct i387_fxsave_struct __user *buf,
102  void __user *fpstate,
103  struct _fpx_sw_bytes *fx_sw)
104 {
105  int min_xstate_size = sizeof(struct i387_fxsave_struct) +
107  unsigned int magic2;
108 
109  if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
110  return -1;
111 
112  /* Check for the first magic field and other error scenarios. */
113  if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
114  fx_sw->xstate_size < min_xstate_size ||
115  fx_sw->xstate_size > xstate_size ||
116  fx_sw->xstate_size > fx_sw->extended_size)
117  return -1;
118 
119  /*
120  * Check for the presence of second magic word at the end of memory
121  * layout. This detects the case where the user just copied the legacy
122  * fpstate layout with out copying the extended state information
123  * in the memory layout.
124  */
125  if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
126  || magic2 != FP_XSTATE_MAGIC2)
127  return -1;
128 
129  return 0;
130 }
131 
132 /*
133  * Signal frame handlers.
134  */
135 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
136 {
137  if (use_fxsr()) {
138  struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
139  struct user_i387_ia32_struct env;
140  struct _fpstate_ia32 __user *fp = buf;
141 
142  convert_from_fxsr(&env, tsk);
143 
144  if (__copy_to_user(buf, &env, sizeof(env)) ||
145  __put_user(xsave->i387.swd, &fp->status) ||
147  return -1;
148  } else {
149  struct i387_fsave_struct __user *fp = buf;
150  u32 swd;
151  if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
152  return -1;
153  }
154 
155  return 0;
156 }
157 
158 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
159 {
160  struct xsave_struct __user *x = buf;
161  struct _fpx_sw_bytes *sw_bytes;
162  u32 xstate_bv;
163  int err;
164 
165  /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
166  sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
167  err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
168 
169  if (!use_xsave())
170  return err;
171 
172  err |= __put_user(FP_XSTATE_MAGIC2, (__u32 *)(buf + xstate_size));
173 
174  /*
175  * Read the xstate_bv which we copied (directly from the cpu or
176  * from the state in task struct) to the user buffers.
177  */
178  err |= __get_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
179 
180  /*
181  * For legacy compatible, we always set FP/SSE bits in the bit
182  * vector while saving the state to the user context. This will
183  * enable us capturing any changes(during sigreturn) to
184  * the FP/SSE bits by the legacy applications which don't touch
185  * xstate_bv in the xsave header.
186  *
187  * xsave aware apps can change the xstate_bv in the xsave
188  * header as well as change any contents in the memory layout.
189  * xrestore as part of sigreturn will capture all the changes.
190  */
191  xstate_bv |= XSTATE_FPSSE;
192 
193  err |= __put_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
194 
195  return err;
196 }
197 
198 static inline int save_user_xstate(struct xsave_struct __user *buf)
199 {
200  int err;
201 
202  if (use_xsave())
203  err = xsave_user(buf);
204  else if (use_fxsr())
205  err = fxsave_user((struct i387_fxsave_struct __user *) buf);
206  else
207  err = fsave_user((struct i387_fsave_struct __user *) buf);
208 
209  if (unlikely(err) && __clear_user(buf, xstate_size))
210  err = -EFAULT;
211  return err;
212 }
213 
214 /*
215  * Save the fpu, extended register state to the user signal frame.
216  *
217  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
218  * state is copied.
219  * 'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
220  *
221  * buf == buf_fx for 64-bit frames and 32-bit fsave frame.
222  * buf != buf_fx for 32-bit frames with fxstate.
223  *
224  * If the fpu, extended register state is live, save the state directly
225  * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
226  * copy the thread's fpu state to the user frame starting at 'buf_fx'.
227  *
228  * If this is a 32-bit frame with fxstate, put a fsave header before
229  * the aligned state at 'buf_fx'.
230  *
231  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
232  * indicating the absence/presence of the extended state to the user.
233  */
234 int save_xstate_sig(void __user *buf, void __user *buf_fx, int size)
235 {
236  struct xsave_struct *xsave = &current->thread.fpu.state->xsave;
237  struct task_struct *tsk = current;
238  int ia32_fxstate = (buf != buf_fx);
239 
240  ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
241  config_enabled(CONFIG_IA32_EMULATION));
242 
243  if (!access_ok(VERIFY_WRITE, buf, size))
244  return -EACCES;
245 
246  if (!HAVE_HWFP)
247  return fpregs_soft_get(current, NULL, 0,
248  sizeof(struct user_i387_ia32_struct), NULL,
249  (struct _fpstate_ia32 __user *) buf) ? -1 : 1;
250 
251  if (user_has_fpu()) {
252  /* Save the live register state to the user directly. */
253  if (save_user_xstate(buf_fx))
254  return -1;
255  /* Update the thread's fxstate to save the fsave header. */
256  if (ia32_fxstate)
257  fpu_fxsave(&tsk->thread.fpu);
258  } else {
259  sanitize_i387_state(tsk);
260  if (__copy_to_user(buf_fx, xsave, xstate_size))
261  return -1;
262  }
263 
264  /* Save the fsave header for the 32-bit frames. */
265  if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
266  return -1;
267 
268  if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
269  return -1;
270 
271  drop_init_fpu(tsk); /* trigger finit */
272 
273  return 0;
274 }
275 
276 static inline void
277 sanitize_restored_xstate(struct task_struct *tsk,
278  struct user_i387_ia32_struct *ia32_env,
279  u64 xstate_bv, int fx_only)
280 {
281  struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
282  struct xsave_hdr_struct *xsave_hdr = &xsave->xsave_hdr;
283 
284  if (use_xsave()) {
285  /* These bits must be zero. */
286  xsave_hdr->reserved1[0] = xsave_hdr->reserved1[1] = 0;
287 
288  /*
289  * Init the state that is not present in the memory
290  * layout and not enabled by the OS.
291  */
292  if (fx_only)
293  xsave_hdr->xstate_bv = XSTATE_FPSSE;
294  else
295  xsave_hdr->xstate_bv &= (pcntxt_mask & xstate_bv);
296  }
297 
298  if (use_fxsr()) {
299  /*
300  * mscsr reserved bits must be masked to zero for security
301  * reasons.
302  */
303  xsave->i387.mxcsr &= mxcsr_feature_mask;
304 
305  convert_to_fxsr(tsk, ia32_env);
306  }
307 }
308 
309 /*
310  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
311  */
312 static inline int restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
313 {
314  if (use_xsave()) {
315  if ((unsigned long)buf % 64 || fx_only) {
316  u64 init_bv = pcntxt_mask & ~XSTATE_FPSSE;
317  xrstor_state(init_xstate_buf, init_bv);
318  return fxrstor_user(buf);
319  } else {
320  u64 init_bv = pcntxt_mask & ~xbv;
321  if (unlikely(init_bv))
322  xrstor_state(init_xstate_buf, init_bv);
323  return xrestore_user(buf, xbv);
324  }
325  } else if (use_fxsr()) {
326  return fxrstor_user(buf);
327  } else
328  return frstor_user(buf);
329 }
330 
331 int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
332 {
333  int ia32_fxstate = (buf != buf_fx);
334  struct task_struct *tsk = current;
335  int state_size = xstate_size;
336  u64 xstate_bv = 0;
337  int fx_only = 0;
338 
339  ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
340  config_enabled(CONFIG_IA32_EMULATION));
341 
342  if (!buf) {
343  drop_init_fpu(tsk);
344  return 0;
345  }
346 
347  if (!access_ok(VERIFY_READ, buf, size))
348  return -EACCES;
349 
350  if (!used_math() && init_fpu(tsk))
351  return -1;
352 
353  if (!HAVE_HWFP) {
354  return fpregs_soft_set(current, NULL,
355  0, sizeof(struct user_i387_ia32_struct),
356  NULL, buf) != 0;
357  }
358 
359  if (use_xsave()) {
360  struct _fpx_sw_bytes fx_sw_user;
361  if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
362  /*
363  * Couldn't find the extended state information in the
364  * memory layout. Restore just the FP/SSE and init all
365  * the other extended state.
366  */
367  state_size = sizeof(struct i387_fxsave_struct);
368  fx_only = 1;
369  } else {
370  state_size = fx_sw_user.xstate_size;
371  xstate_bv = fx_sw_user.xstate_bv;
372  }
373  }
374 
375  if (ia32_fxstate) {
376  /*
377  * For 32-bit frames with fxstate, copy the user state to the
378  * thread's fpu state, reconstruct fxstate from the fsave
379  * header. Sanitize the copied state etc.
380  */
381  struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
382  struct user_i387_ia32_struct env;
383  int err = 0;
384 
385  /*
386  * Drop the current fpu which clears used_math(). This ensures
387  * that any context-switch during the copy of the new state,
388  * avoids the intermediate state from getting restored/saved.
389  * Thus avoiding the new restored state from getting corrupted.
390  * We will be ready to restore/save the state only after
391  * set_used_math() is again set.
392  */
393  drop_fpu(tsk);
394 
395  if (__copy_from_user(xsave, buf_fx, state_size) ||
396  __copy_from_user(&env, buf, sizeof(env))) {
397  err = -1;
398  } else {
399  sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
400  set_used_math();
401  }
402 
403  if (use_eager_fpu())
405 
406  return err;
407  } else {
408  /*
409  * For 64-bit frames and 32-bit fsave frames, restore the user
410  * state to the registers directly (with exceptions handled).
411  */
412  user_fpu_begin();
413  if (restore_user_xstate(buf_fx, xstate_bv, fx_only)) {
414  drop_init_fpu(tsk);
415  return -1;
416  }
417  }
418 
419  return 0;
420 }
421 
422 /*
423  * Prepare the SW reserved portion of the fxsave memory layout, indicating
424  * the presence of the extended state information in the memory layout
425  * pointed by the fpstate pointer in the sigcontext.
426  * This will be saved when ever the FP and extended state context is
427  * saved on the user stack during the signal handler delivery to the user.
428  */
429 static void prepare_fx_sw_frame(void)
430 {
431  int fsave_header_size = sizeof(struct i387_fsave_struct);
433 
434  if (config_enabled(CONFIG_X86_32))
435  size += fsave_header_size;
436 
437  fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
438  fx_sw_reserved.extended_size = size;
439  fx_sw_reserved.xstate_bv = pcntxt_mask;
440  fx_sw_reserved.xstate_size = xstate_size;
441 
442  if (config_enabled(CONFIG_IA32_EMULATION)) {
443  fx_sw_reserved_ia32 = fx_sw_reserved;
444  fx_sw_reserved_ia32.extended_size += fsave_header_size;
445  }
446 }
447 
448 /*
449  * Enable the extended processor state save/restore feature
450  */
451 static inline void xstate_enable(void)
452 {
453  set_in_cr4(X86_CR4_OSXSAVE);
455 }
456 
457 /*
458  * Record the offsets and sizes of different state managed by the xsave
459  * memory layout.
460  */
461 static void __init setup_xstate_features(void)
462 {
463  int eax, ebx, ecx, edx, leaf = 0x2;
464 
465  xstate_features = fls64(pcntxt_mask);
466  xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
467  xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
468 
469  do {
470  cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
471 
472  if (eax == 0)
473  break;
474 
475  xstate_offsets[leaf] = ebx;
476  xstate_sizes[leaf] = eax;
477 
478  leaf++;
479  } while (1);
480 }
481 
482 /*
483  * setup the xstate image representing the init state
484  */
485 static void __init setup_init_fpu_buf(void)
486 {
487  /*
488  * Setup init_xstate_buf to represent the init state of
489  * all the features managed by the xsave
490  */
491  init_xstate_buf = alloc_bootmem_align(xstate_size,
492  __alignof__(struct xsave_struct));
493  fx_finit(&init_xstate_buf->i387);
494 
495  if (!cpu_has_xsave)
496  return;
497 
498  setup_xstate_features();
499 
500  /*
501  * Init all the features state with header_bv being 0x0
502  */
503  xrstor_state(init_xstate_buf, -1);
504  /*
505  * Dump the init state again. This is to identify the init state
506  * of any feature which is not represented by all zero's.
507  */
508  xsave_state(init_xstate_buf, -1);
509 }
510 
511 static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
512 static int __init eager_fpu_setup(char *s)
513 {
514  if (!strcmp(s, "on"))
515  eagerfpu = ENABLE;
516  else if (!strcmp(s, "off"))
517  eagerfpu = DISABLE;
518  else if (!strcmp(s, "auto"))
519  eagerfpu = AUTO;
520  return 1;
521 }
522 __setup("eagerfpu=", eager_fpu_setup);
523 
524 /*
525  * Enable and initialize the xsave feature.
526  */
527 static void __init xstate_enable_boot_cpu(void)
528 {
529  unsigned int eax, ebx, ecx, edx;
530 
531  if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
532  WARN(1, KERN_ERR "XSTATE_CPUID missing\n");
533  return;
534  }
535 
536  cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
537  pcntxt_mask = eax + ((u64)edx << 32);
538 
539  if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
540  pr_err("FP/SSE not shown under xsave features 0x%llx\n",
541  pcntxt_mask);
542  BUG();
543  }
544 
545  /*
546  * Support only the state known to OS.
547  */
549 
550  xstate_enable();
551 
552  /*
553  * Recompute the context size for enabled features
554  */
555  cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
556  xstate_size = ebx;
557 
559  prepare_fx_sw_frame();
560  setup_init_fpu_buf();
561 
562  /* Auto enable eagerfpu for xsaveopt */
563  if (cpu_has_xsaveopt && eagerfpu != DISABLE)
564  eagerfpu = ENABLE;
565 
566  pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
568 }
569 
570 /*
571  * For the very first instance, this calls xstate_enable_boot_cpu();
572  * for all subsequent instances, this calls xstate_enable().
573  *
574  * This is somewhat obfuscated due to the lack of powerful enough
575  * overrides for the section checks.
576  */
578 {
579  static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
580  void (*this_func)(void);
581 
582  if (!cpu_has_xsave)
583  return;
584 
585  this_func = next_func;
586  next_func = xstate_enable;
587  this_func();
588 }
589 
590 static inline void __init eager_fpu_init_bp(void)
591 {
592  current->thread.fpu.state =
593  alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
594  if (!init_xstate_buf)
595  setup_init_fpu_buf();
596 }
597 
599 {
600  static __refdata void (*boot_func)(void) = eager_fpu_init_bp;
601 
602  clear_used_math();
603  current_thread_info()->status = 0;
604 
605  if (eagerfpu == ENABLE)
606  setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
607 
608  if (!cpu_has_eager_fpu) {
609  stts();
610  return;
611  }
612 
613  if (boot_func) {
614  boot_func();
615  boot_func = NULL;
616  }
617 
618  /*
619  * This is same as math_state_restore(). But use_xsave() is
620  * not yet patched to use math_state_restore().
621  */
622  init_fpu(current);
623  __thread_fpu_begin(current);
624  if (cpu_has_xsave)
625  xrstor_state(init_xstate_buf, -1);
626  else
627  fxrstor_checking(&init_xstate_buf->i387);
628 }