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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/signal.h>
11#include <asm/fpu/regset.h>
12#include <asm/fpu/xstate.h>
13
14#include <asm/sigframe.h>
15#include <asm/trapnr.h>
16#include <asm/trace/fpu.h>
17
18#include "context.h"
19#include "internal.h"
20#include "legacy.h"
21#include "xstate.h"
22
23/*
24 * Check for the presence of extended state information in the
25 * user fpstate pointer in the sigcontext.
26 */
27static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
28 struct _fpx_sw_bytes *fx_sw)
29{
30 int min_xstate_size = sizeof(struct fxregs_state) +
31 sizeof(struct xstate_header);
32 void __user *fpstate = fxbuf;
33 unsigned int magic2;
34
35 if (__copy_from_user(fx_sw, &fxbuf->sw_reserved[0], sizeof(*fx_sw)))
36 return false;
37
38 /* Check for the first magic field and other error scenarios. */
39 if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
40 fx_sw->xstate_size < min_xstate_size ||
41 fx_sw->xstate_size > current->thread.fpu.fpstate->user_size ||
42 fx_sw->xstate_size > fx_sw->extended_size)
43 goto setfx;
44
45 /*
46 * Check for the presence of second magic word at the end of memory
47 * layout. This detects the case where the user just copied the legacy
48 * fpstate layout with out copying the extended state information
49 * in the memory layout.
50 */
51 if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size)))
52 return false;
53
54 if (likely(magic2 == FP_XSTATE_MAGIC2))
55 return true;
56setfx:
57 trace_x86_fpu_xstate_check_failed(¤t->thread.fpu);
58
59 /* Set the parameters for fx only state */
60 fx_sw->magic1 = 0;
61 fx_sw->xstate_size = sizeof(struct fxregs_state);
62 fx_sw->xfeatures = XFEATURE_MASK_FPSSE;
63 return true;
64}
65
66/*
67 * Signal frame handlers.
68 */
69static inline bool save_fsave_header(struct task_struct *tsk, void __user *buf)
70{
71 if (use_fxsr()) {
72 struct xregs_state *xsave = &tsk->thread.fpu.fpstate->regs.xsave;
73 struct user_i387_ia32_struct env;
74 struct _fpstate_32 __user *fp = buf;
75
76 fpregs_lock();
77 if (!test_thread_flag(TIF_NEED_FPU_LOAD))
78 fxsave(&tsk->thread.fpu.fpstate->regs.fxsave);
79 fpregs_unlock();
80
81 convert_from_fxsr(&env, tsk);
82
83 if (__copy_to_user(buf, &env, sizeof(env)) ||
84 __put_user(xsave->i387.swd, &fp->status) ||
85 __put_user(X86_FXSR_MAGIC, &fp->magic))
86 return false;
87 } else {
88 struct fregs_state __user *fp = buf;
89 u32 swd;
90
91 if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
92 return false;
93 }
94
95 return true;
96}
97
98/*
99 * Prepare the SW reserved portion of the fxsave memory layout, indicating
100 * the presence of the extended state information in the memory layout
101 * pointed to by the fpstate pointer in the sigcontext.
102 * This is saved when ever the FP and extended state context is
103 * saved on the user stack during the signal handler delivery to the user.
104 */
105static inline void save_sw_bytes(struct _fpx_sw_bytes *sw_bytes, bool ia32_frame,
106 struct fpstate *fpstate)
107{
108 sw_bytes->magic1 = FP_XSTATE_MAGIC1;
109 sw_bytes->extended_size = fpstate->user_size + FP_XSTATE_MAGIC2_SIZE;
110 sw_bytes->xfeatures = fpstate->user_xfeatures;
111 sw_bytes->xstate_size = fpstate->user_size;
112
113 if (ia32_frame)
114 sw_bytes->extended_size += sizeof(struct fregs_state);
115}
116
117static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
118 struct fpstate *fpstate)
119{
120 struct xregs_state __user *x = buf;
121 struct _fpx_sw_bytes sw_bytes = {};
122 u32 xfeatures;
123 int err;
124
125 /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
126 save_sw_bytes(&sw_bytes, ia32_frame, fpstate);
127 err = __copy_to_user(&x->i387.sw_reserved, &sw_bytes, sizeof(sw_bytes));
128
129 if (!use_xsave())
130 return !err;
131
132 err |= __put_user(FP_XSTATE_MAGIC2,
133 (__u32 __user *)(buf + fpstate->user_size));
134
135 /*
136 * Read the xfeatures which we copied (directly from the cpu or
137 * from the state in task struct) to the user buffers.
138 */
139 err |= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
140
141 /*
142 * For legacy compatible, we always set FP/SSE bits in the bit
143 * vector while saving the state to the user context. This will
144 * enable us capturing any changes(during sigreturn) to
145 * the FP/SSE bits by the legacy applications which don't touch
146 * xfeatures in the xsave header.
147 *
148 * xsave aware apps can change the xfeatures in the xsave
149 * header as well as change any contents in the memory layout.
150 * xrestore as part of sigreturn will capture all the changes.
151 */
152 xfeatures |= XFEATURE_MASK_FPSSE;
153
154 err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
155
156 return !err;
157}
158
159static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pkru)
160{
161 if (use_xsave())
162 return xsave_to_user_sigframe(buf, pkru);
163
164 if (use_fxsr())
165 return fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
166 else
167 return fnsave_to_user_sigframe((struct fregs_state __user *) buf);
168}
169
170/*
171 * Save the fpu, extended register state to the user signal frame.
172 *
173 * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
174 * state is copied.
175 * 'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
176 *
177 * buf == buf_fx for 64-bit frames and 32-bit fsave frame.
178 * buf != buf_fx for 32-bit frames with fxstate.
179 *
180 * Save it directly to the user frame with disabled page fault handler. If
181 * that faults, try to clear the frame which handles the page fault.
182 *
183 * If this is a 32-bit frame with fxstate, put a fsave header before
184 * the aligned state at 'buf_fx'.
185 *
186 * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
187 * indicating the absence/presence of the extended state to the user.
188 */
189bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u32 pkru)
190{
191 struct task_struct *tsk = current;
192 struct fpstate *fpstate = tsk->thread.fpu.fpstate;
193 bool ia32_fxstate = (buf != buf_fx);
194 int ret;
195
196 ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
197 IS_ENABLED(CONFIG_IA32_EMULATION));
198
199 if (!static_cpu_has(X86_FEATURE_FPU)) {
200 struct user_i387_ia32_struct fp;
201
202 fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
203 .left = sizeof(fp)});
204 return !copy_to_user(buf, &fp, sizeof(fp));
205 }
206
207 if (!access_ok(buf, size))
208 return false;
209
210 if (use_xsave()) {
211 struct xregs_state __user *xbuf = buf_fx;
212
213 /*
214 * Clear the xsave header first, so that reserved fields are
215 * initialized to zero.
216 */
217 if (__clear_user(&xbuf->header, sizeof(xbuf->header)))
218 return false;
219 }
220retry:
221 /*
222 * Load the FPU registers if they are not valid for the current task.
223 * With a valid FPU state we can attempt to save the state directly to
224 * userland's stack frame which will likely succeed. If it does not,
225 * resolve the fault in the user memory and try again.
226 */
227 fpregs_lock();
228 if (test_thread_flag(TIF_NEED_FPU_LOAD))
229 fpregs_restore_userregs();
230
231 pagefault_disable();
232 ret = copy_fpregs_to_sigframe(buf_fx, pkru);
233 pagefault_enable();
234 fpregs_unlock();
235
236 if (ret) {
237 if (!__clear_user(buf_fx, fpstate->user_size))
238 goto retry;
239 return false;
240 }
241
242 /* Save the fsave header for the 32-bit frames. */
243 if ((ia32_fxstate || !use_fxsr()) && !save_fsave_header(tsk, buf))
244 return false;
245
246 if (use_fxsr() && !save_xstate_epilog(buf_fx, ia32_fxstate, fpstate))
247 return false;
248
249 return true;
250}
251
252static int __restore_fpregs_from_user(void __user *buf, u64 ufeatures,
253 u64 xrestore, bool fx_only)
254{
255 if (use_xsave()) {
256 u64 init_bv = ufeatures & ~xrestore;
257 int ret;
258
259 if (likely(!fx_only))
260 ret = xrstor_from_user_sigframe(buf, xrestore);
261 else
262 ret = fxrstor_from_user_sigframe(buf);
263
264 if (!ret && unlikely(init_bv))
265 os_xrstor(&init_fpstate, init_bv);
266 return ret;
267 } else if (use_fxsr()) {
268 return fxrstor_from_user_sigframe(buf);
269 } else {
270 return frstor_from_user_sigframe(buf);
271 }
272}
273
274/*
275 * Attempt to restore the FPU registers directly from user memory.
276 * Pagefaults are handled and any errors returned are fatal.
277 */
278static bool restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
279{
280 struct fpu *fpu = ¤t->thread.fpu;
281 int ret;
282
283 /* Restore enabled features only. */
284 xrestore &= fpu->fpstate->user_xfeatures;
285retry:
286 fpregs_lock();
287 /* Ensure that XFD is up to date */
288 xfd_update_state(fpu->fpstate);
289 pagefault_disable();
290 ret = __restore_fpregs_from_user(buf, fpu->fpstate->user_xfeatures,
291 xrestore, fx_only);
292 pagefault_enable();
293
294 if (unlikely(ret)) {
295 /*
296 * The above did an FPU restore operation, restricted to
297 * the user portion of the registers, and failed, but the
298 * microcode might have modified the FPU registers
299 * nevertheless.
300 *
301 * If the FPU registers do not belong to current, then
302 * invalidate the FPU register state otherwise the task
303 * might preempt current and return to user space with
304 * corrupted FPU registers.
305 */
306 if (test_thread_flag(TIF_NEED_FPU_LOAD))
307 __cpu_invalidate_fpregs_state();
308 fpregs_unlock();
309
310 /* Try to handle #PF, but anything else is fatal. */
311 if (ret != X86_TRAP_PF)
312 return false;
313
314 if (!fault_in_readable(buf, fpu->fpstate->user_size))
315 goto retry;
316 return false;
317 }
318
319 /*
320 * Restore supervisor states: previous context switch etc has done
321 * XSAVES and saved the supervisor states in the kernel buffer from
322 * which they can be restored now.
323 *
324 * It would be optimal to handle this with a single XRSTORS, but
325 * this does not work because the rest of the FPU registers have
326 * been restored from a user buffer directly.
327 */
328 if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
329 os_xrstor_supervisor(fpu->fpstate);
330
331 fpregs_mark_activate();
332 fpregs_unlock();
333 return true;
334}
335
336static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
337 bool ia32_fxstate)
338{
339 struct task_struct *tsk = current;
340 struct fpu *fpu = &tsk->thread.fpu;
341 struct user_i387_ia32_struct env;
342 bool success, fx_only = false;
343 union fpregs_state *fpregs;
344 u64 user_xfeatures = 0;
345
346 if (use_xsave()) {
347 struct _fpx_sw_bytes fx_sw_user;
348
349 if (!check_xstate_in_sigframe(buf_fx, &fx_sw_user))
350 return false;
351
352 fx_only = !fx_sw_user.magic1;
353 user_xfeatures = fx_sw_user.xfeatures;
354 } else {
355 user_xfeatures = XFEATURE_MASK_FPSSE;
356 }
357
358 if (likely(!ia32_fxstate)) {
359 /* Restore the FPU registers directly from user memory. */
360 return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only);
361 }
362
363 /*
364 * Copy the legacy state because the FP portion of the FX frame has
365 * to be ignored for histerical raisins. The legacy state is folded
366 * in once the larger state has been copied.
367 */
368 if (__copy_from_user(&env, buf, sizeof(env)))
369 return false;
370
371 /*
372 * By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is
373 * not modified on context switch and that the xstate is considered
374 * to be loaded again on return to userland (overriding last_cpu avoids
375 * the optimisation).
376 */
377 fpregs_lock();
378 if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
379 /*
380 * If supervisor states are available then save the
381 * hardware state in current's fpstate so that the
382 * supervisor state is preserved. Save the full state for
383 * simplicity. There is no point in optimizing this by only
384 * saving the supervisor states and then shuffle them to
385 * the right place in memory. It's ia32 mode. Shrug.
386 */
387 if (xfeatures_mask_supervisor())
388 os_xsave(fpu->fpstate);
389 set_thread_flag(TIF_NEED_FPU_LOAD);
390 }
391 __fpu_invalidate_fpregs_state(fpu);
392 __cpu_invalidate_fpregs_state();
393 fpregs_unlock();
394
395 fpregs = &fpu->fpstate->regs;
396 if (use_xsave() && !fx_only) {
397 if (copy_sigframe_from_user_to_xstate(tsk, buf_fx))
398 return false;
399 } else {
400 if (__copy_from_user(&fpregs->fxsave, buf_fx,
401 sizeof(fpregs->fxsave)))
402 return false;
403
404 if (IS_ENABLED(CONFIG_X86_64)) {
405 /* Reject invalid MXCSR values. */
406 if (fpregs->fxsave.mxcsr & ~mxcsr_feature_mask)
407 return false;
408 } else {
409 /* Mask invalid bits out for historical reasons (broken hardware). */
410 fpregs->fxsave.mxcsr &= mxcsr_feature_mask;
411 }
412
413 /* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
414 if (use_xsave())
415 fpregs->xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;
416 }
417
418 /* Fold the legacy FP storage */
419 convert_to_fxsr(&fpregs->fxsave, &env);
420
421 fpregs_lock();
422 if (use_xsave()) {
423 /*
424 * Remove all UABI feature bits not set in user_xfeatures
425 * from the memory xstate header which makes the full
426 * restore below bring them into init state. This works for
427 * fx_only mode as well because that has only FP and SSE
428 * set in user_xfeatures.
429 *
430 * Preserve supervisor states!
431 */
432 u64 mask = user_xfeatures | xfeatures_mask_supervisor();
433
434 fpregs->xsave.header.xfeatures &= mask;
435 success = !os_xrstor_safe(fpu->fpstate,
436 fpu_kernel_cfg.max_features);
437 } else {
438 success = !fxrstor_safe(&fpregs->fxsave);
439 }
440
441 if (likely(success))
442 fpregs_mark_activate();
443
444 fpregs_unlock();
445 return success;
446}
447
448static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
449{
450 unsigned int size = fpstate->user_size;
451
452 return use_xsave() ? size + FP_XSTATE_MAGIC2_SIZE : size;
453}
454
455/*
456 * Restore FPU state from a sigframe:
457 */
458bool fpu__restore_sig(void __user *buf, int ia32_frame)
459{
460 struct fpu *fpu = ¤t->thread.fpu;
461 void __user *buf_fx = buf;
462 bool ia32_fxstate = false;
463 bool success = false;
464 unsigned int size;
465
466 if (unlikely(!buf)) {
467 fpu__clear_user_states(fpu);
468 return true;
469 }
470
471 size = xstate_sigframe_size(fpu->fpstate);
472
473 ia32_frame &= (IS_ENABLED(CONFIG_X86_32) ||
474 IS_ENABLED(CONFIG_IA32_EMULATION));
475
476 /*
477 * Only FXSR enabled systems need the FX state quirk.
478 * FRSTOR does not need it and can use the fast path.
479 */
480 if (ia32_frame && use_fxsr()) {
481 buf_fx = buf + sizeof(struct fregs_state);
482 size += sizeof(struct fregs_state);
483 ia32_fxstate = true;
484 }
485
486 if (!access_ok(buf, size))
487 goto out;
488
489 if (!IS_ENABLED(CONFIG_X86_64) && !cpu_feature_enabled(X86_FEATURE_FPU)) {
490 success = !fpregs_soft_set(current, NULL, 0,
491 sizeof(struct user_i387_ia32_struct),
492 NULL, buf);
493 } else {
494 success = __fpu_restore_sig(buf, buf_fx, ia32_fxstate);
495 }
496
497out:
498 if (unlikely(!success))
499 fpu__clear_user_states(fpu);
500 return success;
501}
502
503unsigned long
504fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
505 unsigned long *buf_fx, unsigned long *size)
506{
507 unsigned long frame_size = xstate_sigframe_size(current->thread.fpu.fpstate);
508
509 *buf_fx = sp = round_down(sp - frame_size, 64);
510 if (ia32_frame && use_fxsr()) {
511 frame_size += sizeof(struct fregs_state);
512 sp -= sizeof(struct fregs_state);
513 }
514
515 *size = frame_size;
516
517 return sp;
518}
519
520unsigned long __init fpu__get_fpstate_size(void)
521{
522 unsigned long ret = fpu_user_cfg.max_size;
523
524 if (use_xsave())
525 ret += FP_XSTATE_MAGIC2_SIZE;
526
527 /*
528 * This space is needed on (most) 32-bit kernels, or when a 32-bit
529 * app is running on a 64-bit kernel. To keep things simple, just
530 * assume the worst case and always include space for 'freg_state',
531 * even for 64-bit apps on 64-bit kernels. This wastes a bit of
532 * space, but keeps the code simple.
533 */
534 if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||
535 IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
536 ret += sizeof(struct fregs_state);
537
538 return ret;
539}
540