signal.c

  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	void __user *fpstate = fxbuf;
 31	unsigned int magic2;
 32
 33	if (__copy_from_user(fx_sw, &fxbuf->sw_reserved[0], sizeof(*fx_sw)))
 34		return false;
 35
 36	/* Check for the first magic field */
 37	if (fx_sw->magic1 != FP_XSTATE_MAGIC1)
 38		goto setfx;
 39
 40	/*
 41	 * Check for the presence of second magic word at the end of memory
 42	 * layout. This detects the case where the user just copied the legacy
 43	 * fpstate layout with out copying the extended state information
 44	 * in the memory layout.
 45	 */
 46	if (__get_user(magic2, (__u32 __user *)(fpstate + x86_task_fpu(current)->fpstate->user_size)))
 47		return false;
 48
 49	if (likely(magic2 == FP_XSTATE_MAGIC2))
 50		return true;
 51setfx:
 52	trace_x86_fpu_xstate_check_failed(x86_task_fpu(current));
 53
 54	/* Set the parameters for fx only state */
 55	fx_sw->magic1 = 0;
 56	fx_sw->xstate_size = sizeof(struct fxregs_state);
 57	fx_sw->xfeatures = XFEATURE_MASK_FPSSE;
 58	return true;
 59}
 60
 61/*
 62 * Signal frame handlers.
 63 */
 64static inline bool save_fsave_header(struct task_struct *tsk, void __user *buf)
 65{
 66	if (use_fxsr()) {
 67		struct xregs_state *xsave = &x86_task_fpu(tsk)->fpstate->regs.xsave;
 68		struct user_i387_ia32_struct env;
 69		struct _fpstate_32 __user *fp = buf;
 70
 71		fpregs_lock();
 72		if (!test_thread_flag(TIF_NEED_FPU_LOAD))
 73			fxsave(&x86_task_fpu(tsk)->fpstate->regs.fxsave);
 74		fpregs_unlock();
 75
 76		convert_from_fxsr(&env, tsk);
 77
 78		if (__copy_to_user(buf, &env, sizeof(env)) ||
 79		    __put_user(xsave->i387.swd, &fp->status) ||
 80		    __put_user(X86_FXSR_MAGIC, &fp->magic))
 81			return false;
 82	} else {
 83		struct fregs_state __user *fp = buf;
 84		u32 swd;
 85
 86		if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
 87			return false;
 88	}
 89
 90	return true;
 91}
 92
 93/*
 94 * Prepare the SW reserved portion of the fxsave memory layout, indicating
 95 * the presence of the extended state information in the memory layout
 96 * pointed to by the fpstate pointer in the sigcontext.
 97 * This is saved when ever the FP and extended state context is
 98 * saved on the user stack during the signal handler delivery to the user.
 99 */
100static inline void save_sw_bytes(struct _fpx_sw_bytes *sw_bytes, bool ia32_frame,
101				 struct fpstate *fpstate)
102{
103	sw_bytes->magic1 = FP_XSTATE_MAGIC1;
104	sw_bytes->extended_size = fpstate->user_size + FP_XSTATE_MAGIC2_SIZE;
105	sw_bytes->xfeatures = fpstate->user_xfeatures;
106	sw_bytes->xstate_size = fpstate->user_size;
107
108	if (ia32_frame)
109		sw_bytes->extended_size += sizeof(struct fregs_state);
110}
111
112static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
113				      struct fpstate *fpstate)
114{
115	struct xregs_state __user *x = buf;
116	struct _fpx_sw_bytes sw_bytes = {};
117	int err;
118
119	/* Setup the bytes not touched by the [f]xsave and reserved for SW. */
120	save_sw_bytes(&sw_bytes, ia32_frame, fpstate);
121	err = __copy_to_user(&x->i387.sw_reserved, &sw_bytes, sizeof(sw_bytes));
122
123	if (!use_xsave())
124		return !err;
125
126	err |= __put_user(FP_XSTATE_MAGIC2,
127			  (__u32 __user *)(buf + fpstate->user_size));
128
129	/*
130	 * For legacy compatible, we always set FP/SSE bits in the bit
131	 * vector while saving the state to the user context. This will
132	 * enable us capturing any changes(during sigreturn) to
133	 * the FP/SSE bits by the legacy applications which don't touch
134	 * xfeatures in the xsave header.
135	 *
136	 * xsave aware apps can change the xfeatures in the xsave
137	 * header as well as change any contents in the memory layout.
138	 * xrestore as part of sigreturn will capture all the changes.
139	 */
140	err |= set_xfeature_in_sigframe(x, XFEATURE_MASK_FPSSE);
141
142	return !err;
143}
144
145static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pkru)
146{
147	if (use_xsave())
148		return xsave_to_user_sigframe(buf, pkru);
149
150	if (use_fxsr())
151		return fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
152	else
153		return fnsave_to_user_sigframe((struct fregs_state __user *) buf);
154}
155
156/*
157 * Save the fpu, extended register state to the user signal frame.
158 *
159 * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
160 *  state is copied.
161 *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
162 *
163 *	buf == buf_fx for 64-bit frames and 32-bit fsave frame.
164 *	buf != buf_fx for 32-bit frames with fxstate.
165 *
166 * Save it directly to the user frame with disabled page fault handler. If
167 * that faults, try to clear the frame which handles the page fault.
168 *
169 * If this is a 32-bit frame with fxstate, put a fsave header before
170 * the aligned state at 'buf_fx'.
171 *
172 * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
173 * indicating the absence/presence of the extended state to the user.
174 */
175bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u32 pkru)
176{
177	struct task_struct *tsk = current;
178	struct fpstate *fpstate = x86_task_fpu(tsk)->fpstate;
179	bool ia32_fxstate = (buf != buf_fx);
180	int ret;
181
182	ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
183			 IS_ENABLED(CONFIG_IA32_EMULATION));
184
185	if (!static_cpu_has(X86_FEATURE_FPU)) {
186		struct user_i387_ia32_struct fp;
187
188		fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
189						.left = sizeof(fp)});
190		return !copy_to_user(buf, &fp, sizeof(fp));
191	}
192
193	if (!access_ok(buf, size))
194		return false;
195
196	if (use_xsave()) {
197		struct xregs_state __user *xbuf = buf_fx;
198
199		/*
200		 * Clear the xsave header first, so that reserved fields are
201		 * initialized to zero.
202		 */
203		if (__clear_user(&xbuf->header, sizeof(xbuf->header)))
204			return false;
205	}
206retry:
207	/*
208	 * Load the FPU registers if they are not valid for the current task.
209	 * With a valid FPU state we can attempt to save the state directly to
210	 * userland's stack frame which will likely succeed. If it does not,
211	 * resolve the fault in the user memory and try again.
212	 */
213	fpregs_lock();
214	if (test_thread_flag(TIF_NEED_FPU_LOAD))
215		fpregs_restore_userregs();
216
217	pagefault_disable();
218	ret = copy_fpregs_to_sigframe(buf_fx, pkru);
219	pagefault_enable();
220	fpregs_unlock();
221
222	if (ret) {
223		if (!__clear_user(buf_fx, fpstate->user_size))
224			goto retry;
225		return false;
226	}
227
228	/* Save the fsave header for the 32-bit frames. */
229	if ((ia32_fxstate || !use_fxsr()) && !save_fsave_header(tsk, buf))
230		return false;
231
232	if (use_fxsr() && !save_xstate_epilog(buf_fx, ia32_fxstate, fpstate))
233		return false;
234
235	return true;
236}
237
238static int __restore_fpregs_from_user(void __user *buf, u64 ufeatures,
239				      u64 xrestore, bool fx_only)
240{
241	if (use_xsave()) {
242		u64 init_bv = ufeatures & ~xrestore;
243		int ret;
244
245		if (likely(!fx_only))
246			ret = xrstor_from_user_sigframe(buf, xrestore);
247		else
248			ret = fxrstor_from_user_sigframe(buf);
249
250		if (!ret && unlikely(init_bv))
251			os_xrstor(&init_fpstate, init_bv);
252		return ret;
253	} else if (use_fxsr()) {
254		return fxrstor_from_user_sigframe(buf);
255	} else {
256		return frstor_from_user_sigframe(buf);
257	}
258}
259
260/*
261 * Attempt to restore the FPU registers directly from user memory.
262 * Pagefaults are handled and any errors returned are fatal.
263 */
264static bool restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
265{
266	struct fpu *fpu = x86_task_fpu(current);
267	int ret;
268
269	/* Restore enabled features only. */
270	xrestore &= fpu->fpstate->user_xfeatures;
271retry:
272	fpregs_lock();
273	/* Ensure that XFD is up to date */
274	xfd_update_state(fpu->fpstate);
275	pagefault_disable();
276	ret = __restore_fpregs_from_user(buf, fpu->fpstate->user_xfeatures,
277					 xrestore, fx_only);
278	pagefault_enable();
279
280	if (unlikely(ret)) {
281		/*
282		 * The above did an FPU restore operation, restricted to
283		 * the user portion of the registers, and failed, but the
284		 * microcode might have modified the FPU registers
285		 * nevertheless.
286		 *
287		 * If the FPU registers do not belong to current, then
288		 * invalidate the FPU register state otherwise the task
289		 * might preempt current and return to user space with
290		 * corrupted FPU registers.
291		 */
292		if (test_thread_flag(TIF_NEED_FPU_LOAD))
293			__cpu_invalidate_fpregs_state();
294		fpregs_unlock();
295
296		/* Try to handle #PF, but anything else is fatal. */
297		if (ret != X86_TRAP_PF)
298			return false;
299
300		if (!fault_in_readable(buf, fpu->fpstate->user_size))
301			goto retry;
302		return false;
303	}
304
305	/*
306	 * Restore supervisor states: previous context switch etc has done
307	 * XSAVES and saved the supervisor states in the kernel buffer from
308	 * which they can be restored now.
309	 *
310	 * It would be optimal to handle this with a single XRSTORS, but
311	 * this does not work because the rest of the FPU registers have
312	 * been restored from a user buffer directly.
313	 */
314	if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
315		os_xrstor_supervisor(fpu->fpstate);
316
317	fpregs_mark_activate();
318	fpregs_unlock();
319	return true;
320}
321
322static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
323			      bool ia32_fxstate)
324{
325	struct task_struct *tsk = current;
326	struct fpu *fpu = x86_task_fpu(tsk);
327	struct user_i387_ia32_struct env;
328	bool success, fx_only = false;
329	union fpregs_state *fpregs;
330	u64 user_xfeatures = 0;
331
332	if (use_xsave()) {
333		struct _fpx_sw_bytes fx_sw_user;
334
335		if (!check_xstate_in_sigframe(buf_fx, &fx_sw_user))
336			return false;
337
338		fx_only = !fx_sw_user.magic1;
339		user_xfeatures = fx_sw_user.xfeatures;
340	} else {
341		user_xfeatures = XFEATURE_MASK_FPSSE;
342	}
343
344	if (likely(!ia32_fxstate)) {
345		/* Restore the FPU registers directly from user memory. */
346		return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only);
347	}
348
349	/*
350	 * Copy the legacy state because the FP portion of the FX frame has
351	 * to be ignored for histerical raisins. The legacy state is folded
352	 * in once the larger state has been copied.
353	 */
354	if (__copy_from_user(&env, buf, sizeof(env)))
355		return false;
356
357	/*
358	 * By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is
359	 * not modified on context switch and that the xstate is considered
360	 * to be loaded again on return to userland (overriding last_cpu avoids
361	 * the optimisation).
362	 */
363	fpregs_lock();
364	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
365		/*
366		 * If supervisor states are available then save the
367		 * hardware state in current's fpstate so that the
368		 * supervisor state is preserved. Save the full state for
369		 * simplicity. There is no point in optimizing this by only
370		 * saving the supervisor states and then shuffle them to
371		 * the right place in memory. It's ia32 mode. Shrug.
372		 */
373		if (xfeatures_mask_supervisor())
374			os_xsave(fpu->fpstate);
375		set_thread_flag(TIF_NEED_FPU_LOAD);
376	}
377	__fpu_invalidate_fpregs_state(fpu);
378	__cpu_invalidate_fpregs_state();
379	fpregs_unlock();
380
381	fpregs = &fpu->fpstate->regs;
382	if (use_xsave() && !fx_only) {
383		if (copy_sigframe_from_user_to_xstate(tsk, buf_fx))
384			return false;
385	} else {
386		if (__copy_from_user(&fpregs->fxsave, buf_fx,
387				     sizeof(fpregs->fxsave)))
388			return false;
389
390		if (IS_ENABLED(CONFIG_X86_64)) {
391			/* Reject invalid MXCSR values. */
392			if (fpregs->fxsave.mxcsr & ~mxcsr_feature_mask)
393				return false;
394		} else {
395			/* Mask invalid bits out for historical reasons (broken hardware). */
396			fpregs->fxsave.mxcsr &= mxcsr_feature_mask;
397		}
398
399		/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
400		if (use_xsave())
401			fpregs->xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;
402	}
403
404	/* Fold the legacy FP storage */
405	convert_to_fxsr(&fpregs->fxsave, &env);
406
407	fpregs_lock();
408	if (use_xsave()) {
409		/*
410		 * Remove all UABI feature bits not set in user_xfeatures
411		 * from the memory xstate header which makes the full
412		 * restore below bring them into init state. This works for
413		 * fx_only mode as well because that has only FP and SSE
414		 * set in user_xfeatures.
415		 *
416		 * Preserve supervisor states!
417		 */
418		u64 mask = user_xfeatures | xfeatures_mask_supervisor();
419
420		fpregs->xsave.header.xfeatures &= mask;
421		success = !os_xrstor_safe(fpu->fpstate,
422					  fpu_kernel_cfg.max_features);
423	} else {
424		success = !fxrstor_safe(&fpregs->fxsave);
425	}
426
427	if (likely(success))
428		fpregs_mark_activate();
429
430	fpregs_unlock();
431	return success;
432}
433
434static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
435{
436	unsigned int size = fpstate->user_size;
437
438	return use_xsave() ? size + FP_XSTATE_MAGIC2_SIZE : size;
439}
440
441/*
442 * Restore FPU state from a sigframe:
443 */
444bool fpu__restore_sig(void __user *buf, int ia32_frame)
445{
446	struct fpu *fpu = x86_task_fpu(current);
447	void __user *buf_fx = buf;
448	bool ia32_fxstate = false;
449	bool success = false;
450	unsigned int size;
451
452	if (unlikely(!buf)) {
453		fpu__clear_user_states(fpu);
454		return true;
455	}
456
457	size = xstate_sigframe_size(fpu->fpstate);
458
459	ia32_frame &= (IS_ENABLED(CONFIG_X86_32) ||
460		       IS_ENABLED(CONFIG_IA32_EMULATION));
461
462	/*
463	 * Only FXSR enabled systems need the FX state quirk.
464	 * FRSTOR does not need it and can use the fast path.
465	 */
466	if (ia32_frame && use_fxsr()) {
467		buf_fx = buf + sizeof(struct fregs_state);
468		size += sizeof(struct fregs_state);
469		ia32_fxstate = true;
470	}
471
472	if (!access_ok(buf, size))
473		goto out;
474
475	if (!IS_ENABLED(CONFIG_X86_64) && !cpu_feature_enabled(X86_FEATURE_FPU)) {
476		success = !fpregs_soft_set(current, NULL, 0,
477					   sizeof(struct user_i387_ia32_struct),
478					   NULL, buf);
479	} else {
480		success = __fpu_restore_sig(buf, buf_fx, ia32_fxstate);
481	}
482
483out:
484	if (unlikely(!success))
485		fpu__clear_user_states(fpu);
486	return success;
487}
488
489unsigned long
490fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
491		     unsigned long *buf_fx, unsigned long *size)
492{
493	unsigned long frame_size = xstate_sigframe_size(x86_task_fpu(current)->fpstate);
494
495	*buf_fx = sp = round_down(sp - frame_size, 64);
496	if (ia32_frame && use_fxsr()) {
497		frame_size += sizeof(struct fregs_state);
498		sp -= sizeof(struct fregs_state);
499	}
500
501	*size = frame_size;
502
503	return sp;
504}
505
506unsigned long __init fpu__get_fpstate_size(void)
507{
508	unsigned long ret = fpu_user_cfg.max_size;
509
510	if (use_xsave())
511		ret += FP_XSTATE_MAGIC2_SIZE;
512
513	/*
514	 * This space is needed on (most) 32-bit kernels, or when a 32-bit
515	 * app is running on a 64-bit kernel. To keep things simple, just
516	 * assume the worst case and always include space for 'freg_state',
517	 * even for 64-bit apps on 64-bit kernels. This wastes a bit of
518	 * space, but keeps the code simple.
519	 */
520	if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||
521	     IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
522		ret += sizeof(struct fregs_state);
523
524	return ret;
525}
526