1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * mpx.c - Memory Protection eXtensions
4 *
5 * Copyright (c) 2014, Intel Corporation.
6 * Qiaowei Ren <qiaowei.ren@intel.com>
7 * Dave Hansen <dave.hansen@intel.com>
8 */
9 #include <linux/kernel.h>
10 #include <linux/slab.h>
11 #include <linux/mm_types.h>
12 #include <linux/mman.h>
13 #include <linux/syscalls.h>
14 #include <linux/sched/sysctl.h>
15
16 #include <asm/insn.h>
17 #include <asm/insn-eval.h>
18 #include <asm/mmu_context.h>
19 #include <asm/mpx.h>
20 #include <asm/processor.h>
21 #include <asm/fpu/internal.h>
22
23 #define CREATE_TRACE_POINTS
24 #include <asm/trace/mpx.h>
25
26 static inline unsigned long mpx_bd_size_bytes(struct mm_struct *mm)
27 {
28 if (is_64bit_mm(mm))
29 return MPX_BD_SIZE_BYTES_64;
30 else
31 return MPX_BD_SIZE_BYTES_32;
32 }
33
34 static inline unsigned long mpx_bt_size_bytes(struct mm_struct *mm)
35 {
36 if (is_64bit_mm(mm))
37 return MPX_BT_SIZE_BYTES_64;
38 else
39 return MPX_BT_SIZE_BYTES_32;
40 }
41
42 /*
43 * This is really a simplified "vm_mmap". it only handles MPX
44 * bounds tables (the bounds directory is user-allocated).
45 */
46 static unsigned long mpx_mmap(unsigned long len)
47 {
48 struct mm_struct *mm = current->mm;
49 unsigned long addr, populate;
50
51 /* Only bounds table can be allocated here */
52 if (len != mpx_bt_size_bytes(mm))
53 return -EINVAL;
54
55 down_write(&mm->mmap_sem);
56 addr = do_mmap(NULL, 0, len, PROT_READ | PROT_WRITE,
57 MAP_ANONYMOUS | MAP_PRIVATE, VM_MPX, 0, &populate, NULL);
58 up_write(&mm->mmap_sem);
59 if (populate)
60 mm_populate(addr, populate);
61
62 return addr;
63 }
64
65 static int mpx_insn_decode(struct insn *insn,
66 struct pt_regs *regs)
67 {
68 unsigned char buf[MAX_INSN_SIZE];
69 int x86_64 = !test_thread_flag(TIF_IA32);
70 int not_copied;
71 int nr_copied;
72
73 not_copied = copy_from_user(buf, (void __user *)regs->ip, sizeof(buf));
74 nr_copied = sizeof(buf) - not_copied;
75 /*
76 * The decoder _should_ fail nicely if we pass it a short buffer.
77 * But, let's not depend on that implementation detail. If we
78 * did not get anything, just error out now.
79 */
80 if (!nr_copied)
81 return -EFAULT;
82 insn_init(insn, buf, nr_copied, x86_64);
83 insn_get_length(insn);
84 /*
85 * copy_from_user() tries to get as many bytes as we could see in
86 * the largest possible instruction. If the instruction we are
87 * after is shorter than that _and_ we attempt to copy from
88 * something unreadable, we might get a short read. This is OK
89 * as long as the read did not stop in the middle of the
90 * instruction. Check to see if we got a partial instruction.
91 */
92 if (nr_copied < insn->length)
93 return -EFAULT;
94
95 insn_get_opcode(insn);
96 /*
97 * We only _really_ need to decode bndcl/bndcn/bndcu
98 * Error out on anything else.
99 */
100 if (insn->opcode.bytes[0] != 0x0f)
101 goto bad_opcode;
102 if ((insn->opcode.bytes[1] != 0x1a) &&
103 (insn->opcode.bytes[1] != 0x1b))
104 goto bad_opcode;
105
106 return 0;
107 bad_opcode:
108 return -EINVAL;
109 }
110
111 /*
112 * If a bounds overflow occurs then a #BR is generated. This
113 * function decodes MPX instructions to get violation address
114 * and set this address into extended struct siginfo.
115 *
116 * Note that this is not a super precise way of doing this.
117 * Userspace could have, by the time we get here, written
118 * anything it wants in to the instructions. We can not
119 * trust anything about it. They might not be valid
120 * instructions or might encode invalid registers, etc...
121 */
122 int mpx_fault_info(struct mpx_fault_info *info, struct pt_regs *regs)
123 {
124 const struct mpx_bndreg_state *bndregs;
125 const struct mpx_bndreg *bndreg;
126 struct insn insn;
127 uint8_t bndregno;
128 int err;
129
130 err = mpx_insn_decode(&insn, regs);
131 if (err)
132 goto err_out;
133
134 /*
135 * We know at this point that we are only dealing with
136 * MPX instructions.
137 */
138 insn_get_modrm(&insn);
139 bndregno = X86_MODRM_REG(insn.modrm.value);
140 if (bndregno > 3) {
141 err = -EINVAL;
142 goto err_out;
143 }
144 /* get bndregs field from current task's xsave area */
145 bndregs = get_xsave_field_ptr(XFEATURE_BNDREGS);
146 if (!bndregs) {
147 err = -EINVAL;
148 goto err_out;
149 }
150 /* now go select the individual register in the set of 4 */
151 bndreg = &bndregs->bndreg[bndregno];
152
153 /*
154 * The registers are always 64-bit, but the upper 32
155 * bits are ignored in 32-bit mode. Also, note that the
156 * upper bounds are architecturally represented in 1's
157 * complement form.
158 *
159 * The 'unsigned long' cast is because the compiler
160 * complains when casting from integers to different-size
161 * pointers.
162 */
163 info->lower = (void __user *)(unsigned long)bndreg->lower_bound;
164 info->upper = (void __user *)(unsigned long)~bndreg->upper_bound;
165 info->addr = insn_get_addr_ref(&insn, regs);
166
167 /*
168 * We were not able to extract an address from the instruction,
169 * probably because there was something invalid in it.
170 */
171 if (info->addr == (void __user *)-1) {
172 err = -EINVAL;
173 goto err_out;
174 }
175 trace_mpx_bounds_register_exception(info->addr, bndreg);
176 return 0;
177 err_out:
178 /* info might be NULL, but kfree() handles that */
179 return err;
180 }
181
182 static __user void *mpx_get_bounds_dir(void)
183 {
184 const struct mpx_bndcsr *bndcsr;
185
186 if (!cpu_feature_enabled(X86_FEATURE_MPX))
187 return MPX_INVALID_BOUNDS_DIR;
188
189 /*
190 * The bounds directory pointer is stored in a register
191 * only accessible if we first do an xsave.
192 */
193 bndcsr = get_xsave_field_ptr(XFEATURE_BNDCSR);
194 if (!bndcsr)
195 return MPX_INVALID_BOUNDS_DIR;
196
197 /*
198 * Make sure the register looks valid by checking the
199 * enable bit.
200 */
201 if (!(bndcsr->bndcfgu & MPX_BNDCFG_ENABLE_FLAG))
202 return MPX_INVALID_BOUNDS_DIR;
203
204 /*
205 * Lastly, mask off the low bits used for configuration
206 * flags, and return the address of the bounds table.
207 */
208 return (void __user *)(unsigned long)
209 (bndcsr->bndcfgu & MPX_BNDCFG_ADDR_MASK);
210 }
211
212 int mpx_enable_management(void)
213 {
214 void __user *bd_base = MPX_INVALID_BOUNDS_DIR;
215 struct mm_struct *mm = current->mm;
216 int ret = 0;
217
218 /*
219 * runtime in the userspace will be responsible for allocation of
220 * the bounds directory. Then, it will save the base of the bounds
221 * directory into XSAVE/XRSTOR Save Area and enable MPX through
222 * XRSTOR instruction.
223 *
224 * The copy_xregs_to_kernel() beneath get_xsave_field_ptr() is
225 * expected to be relatively expensive. Storing the bounds
226 * directory here means that we do not have to do xsave in the
227 * unmap path; we can just use mm->context.bd_addr instead.
228 */
229 bd_base = mpx_get_bounds_dir();
230 down_write(&mm->mmap_sem);
231
232 /* MPX doesn't support addresses above 47 bits yet. */
233 if (find_vma(mm, DEFAULT_MAP_WINDOW)) {
234 pr_warn_once("%s (%d): MPX cannot handle addresses "
235 "above 47-bits. Disabling.",
236 current->comm, current->pid);
237 ret = -ENXIO;
238 goto out;
239 }
240 mm->context.bd_addr = bd_base;
241 if (mm->context.bd_addr == MPX_INVALID_BOUNDS_DIR)
242 ret = -ENXIO;
243 out:
244 up_write(&mm->mmap_sem);
245 return ret;
246 }
247
248 int mpx_disable_management(void)
249 {
250 struct mm_struct *mm = current->mm;
251
252 if (!cpu_feature_enabled(X86_FEATURE_MPX))
253 return -ENXIO;
254
255 down_write(&mm->mmap_sem);
256 mm->context.bd_addr = MPX_INVALID_BOUNDS_DIR;
257 up_write(&mm->mmap_sem);
258 return 0;
259 }
260
261 static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
262 unsigned long *curval,
263 unsigned long __user *addr,
264 unsigned long old_val, unsigned long new_val)
265 {
266 int ret;
267 /*
268 * user_atomic_cmpxchg_inatomic() actually uses sizeof()
269 * the pointer that we pass to it to figure out how much
270 * data to cmpxchg. We have to be careful here not to
271 * pass a pointer to a 64-bit data type when we only want
272 * a 32-bit copy.
273 */
274 if (is_64bit_mm(mm)) {
275 ret = user_atomic_cmpxchg_inatomic(curval,
276 addr, old_val, new_val);
277 } else {
278 u32 uninitialized_var(curval_32);
279 u32 old_val_32 = old_val;
280 u32 new_val_32 = new_val;
281 u32 __user *addr_32 = (u32 __user *)addr;
282
283 ret = user_atomic_cmpxchg_inatomic(&curval_32,
284 addr_32, old_val_32, new_val_32);
285 *curval = curval_32;
286 }
287 return ret;
288 }
289
290 /*
291 * With 32-bit mode, a bounds directory is 4MB, and the size of each
292 * bounds table is 16KB. With 64-bit mode, a bounds directory is 2GB,
293 * and the size of each bounds table is 4MB.
294 */
295 static int allocate_bt(struct mm_struct *mm, long __user *bd_entry)
296 {
297 unsigned long expected_old_val = 0;
298 unsigned long actual_old_val = 0;
299 unsigned long bt_addr;
300 unsigned long bd_new_entry;
301 int ret = 0;
302
303 /*
304 * Carve the virtual space out of userspace for the new
305 * bounds table:
306 */
307 bt_addr = mpx_mmap(mpx_bt_size_bytes(mm));
308 if (IS_ERR((void *)bt_addr))
309 return PTR_ERR((void *)bt_addr);
310 /*
311 * Set the valid flag (kinda like _PAGE_PRESENT in a pte)
312 */
313 bd_new_entry = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
314
315 /*
316 * Go poke the address of the new bounds table in to the
317 * bounds directory entry out in userspace memory. Note:
318 * we may race with another CPU instantiating the same table.
319 * In that case the cmpxchg will see an unexpected
320 * 'actual_old_val'.
321 *
322 * This can fault, but that's OK because we do not hold
323 * mmap_sem at this point, unlike some of the other part
324 * of the MPX code that have to pagefault_disable().
325 */
326 ret = mpx_cmpxchg_bd_entry(mm, &actual_old_val, bd_entry,
327 expected_old_val, bd_new_entry);
328 if (ret)
329 goto out_unmap;
330
331 /*
332 * The user_atomic_cmpxchg_inatomic() will only return nonzero
333 * for faults, *not* if the cmpxchg itself fails. Now we must
334 * verify that the cmpxchg itself completed successfully.
335 */
336 /*
337 * We expected an empty 'expected_old_val', but instead found
338 * an apparently valid entry. Assume we raced with another
339 * thread to instantiate this table and desclare succecss.
340 */
341 if (actual_old_val & MPX_BD_ENTRY_VALID_FLAG) {
342 ret = 0;
343 goto out_unmap;
344 }
345 /*
346 * We found a non-empty bd_entry but it did not have the
347 * VALID_FLAG set. Return an error which will result in
348 * a SEGV since this probably means that somebody scribbled
349 * some invalid data in to a bounds table.
350 */
351 if (expected_old_val != actual_old_val) {
352 ret = -EINVAL;
353 goto out_unmap;
354 }
355 trace_mpx_new_bounds_table(bt_addr);
356 return 0;
357 out_unmap:
358 vm_munmap(bt_addr, mpx_bt_size_bytes(mm));
359 return ret;
360 }
361
362 /*
363 * When a BNDSTX instruction attempts to save bounds to a bounds
364 * table, it will first attempt to look up the table in the
365 * first-level bounds directory. If it does not find a table in
366 * the directory, a #BR is generated and we get here in order to
367 * allocate a new table.
368 *
369 * With 32-bit mode, the size of BD is 4MB, and the size of each
370 * bound table is 16KB. With 64-bit mode, the size of BD is 2GB,
371 * and the size of each bound table is 4MB.
372 */
373 static int do_mpx_bt_fault(void)
374 {
375 unsigned long bd_entry, bd_base;
376 const struct mpx_bndcsr *bndcsr;
377 struct mm_struct *mm = current->mm;
378
379 bndcsr = get_xsave_field_ptr(XFEATURE_BNDCSR);
380 if (!bndcsr)
381 return -EINVAL;
382 /*
383 * Mask off the preserve and enable bits
384 */
385 bd_base = bndcsr->bndcfgu & MPX_BNDCFG_ADDR_MASK;
386 /*
387 * The hardware provides the address of the missing or invalid
388 * entry via BNDSTATUS, so we don't have to go look it up.
389 */
390 bd_entry = bndcsr->bndstatus & MPX_BNDSTA_ADDR_MASK;
391 /*
392 * Make sure the directory entry is within where we think
393 * the directory is.
394 */
395 if ((bd_entry < bd_base) ||
396 (bd_entry >= bd_base + mpx_bd_size_bytes(mm)))
397 return -EINVAL;
398
399 return allocate_bt(mm, (long __user *)bd_entry);
400 }
401
402 int mpx_handle_bd_fault(void)
403 {
404 /*
405 * Userspace never asked us to manage the bounds tables,
406 * so refuse to help.
407 */
408 if (!kernel_managing_mpx_tables(current->mm))
409 return -EINVAL;
410
411 return do_mpx_bt_fault();
412 }
413
414 /*
415 * A thin wrapper around get_user_pages(). Returns 0 if the
416 * fault was resolved or -errno if not.
417 */
418 static int mpx_resolve_fault(long __user *addr, int write)
419 {
420 long gup_ret;
421 int nr_pages = 1;
422
423 gup_ret = get_user_pages((unsigned long)addr, nr_pages,
424 write ? FOLL_WRITE : 0, NULL, NULL);
425 /*
426 * get_user_pages() returns number of pages gotten.
427 * 0 means we failed to fault in and get anything,
428 * probably because 'addr' is bad.
429 */
430 if (!gup_ret)
431 return -EFAULT;
432 /* Other error, return it */
433 if (gup_ret < 0)
434 return gup_ret;
435 /* must have gup'd a page and gup_ret>0, success */
436 return 0;
437 }
438
439 static unsigned long mpx_bd_entry_to_bt_addr(struct mm_struct *mm,
440 unsigned long bd_entry)
441 {
442 unsigned long bt_addr = bd_entry;
443 int align_to_bytes;
444 /*
445 * Bit 0 in a bt_entry is always the valid bit.
446 */
447 bt_addr &= ~MPX_BD_ENTRY_VALID_FLAG;
448 /*
449 * Tables are naturally aligned at 8-byte boundaries
450 * on 64-bit and 4-byte boundaries on 32-bit. The
451 * documentation makes it appear that the low bits
452 * are ignored by the hardware, so we do the same.
453 */
454 if (is_64bit_mm(mm))
455 align_to_bytes = 8;
456 else
457 align_to_bytes = 4;
458 bt_addr &= ~(align_to_bytes-1);
459 return bt_addr;
460 }
461
462 /*
463 * We only want to do a 4-byte get_user() on 32-bit. Otherwise,
464 * we might run off the end of the bounds table if we are on
465 * a 64-bit kernel and try to get 8 bytes.
466 */
467 static int get_user_bd_entry(struct mm_struct *mm, unsigned long *bd_entry_ret,
468 long __user *bd_entry_ptr)
469 {
470 u32 bd_entry_32;
471 int ret;
472
473 if (is_64bit_mm(mm))
474 return get_user(*bd_entry_ret, bd_entry_ptr);
475
476 /*
477 * Note that get_user() uses the type of the *pointer* to
478 * establish the size of the get, not the destination.
479 */
480 ret = get_user(bd_entry_32, (u32 __user *)bd_entry_ptr);
481 *bd_entry_ret = bd_entry_32;
482 return ret;
483 }
484
485 /*
486 * Get the base of bounds tables pointed by specific bounds
487 * directory entry.
488 */
489 static int get_bt_addr(struct mm_struct *mm,
490 long __user *bd_entry_ptr,
491 unsigned long *bt_addr_result)
492 {
493 int ret;
494 int valid_bit;
495 unsigned long bd_entry;
496 unsigned long bt_addr;
497
498 if (!access_ok((bd_entry_ptr), sizeof(*bd_entry_ptr)))
499 return -EFAULT;
500
501 while (1) {
502 int need_write = 0;
503
504 pagefault_disable();
505 ret = get_user_bd_entry(mm, &bd_entry, bd_entry_ptr);
506 pagefault_enable();
507 if (!ret)
508 break;
509 if (ret == -EFAULT)
510 ret = mpx_resolve_fault(bd_entry_ptr, need_write);
511 /*
512 * If we could not resolve the fault, consider it
513 * userspace's fault and error out.
514 */
515 if (ret)
516 return ret;
517 }
518
519 valid_bit = bd_entry & MPX_BD_ENTRY_VALID_FLAG;
520 bt_addr = mpx_bd_entry_to_bt_addr(mm, bd_entry);
521
522 /*
523 * When the kernel is managing bounds tables, a bounds directory
524 * entry will either have a valid address (plus the valid bit)
525 * *OR* be completely empty. If we see a !valid entry *and* some
526 * data in the address field, we know something is wrong. This
527 * -EINVAL return will cause a SIGSEGV.
528 */
529 if (!valid_bit && bt_addr)
530 return -EINVAL;
531 /*
532 * Do we have an completely zeroed bt entry? That is OK. It
533 * just means there was no bounds table for this memory. Make
534 * sure to distinguish this from -EINVAL, which will cause
535 * a SEGV.
536 */
537 if (!valid_bit)
538 return -ENOENT;
539
540 *bt_addr_result = bt_addr;
541 return 0;
542 }
543
544 static inline int bt_entry_size_bytes(struct mm_struct *mm)
545 {
546 if (is_64bit_mm(mm))
547 return MPX_BT_ENTRY_BYTES_64;
548 else
549 return MPX_BT_ENTRY_BYTES_32;
550 }
551
552 /*
553 * Take a virtual address and turns it in to the offset in bytes
554 * inside of the bounds table where the bounds table entry
555 * controlling 'addr' can be found.
556 */
557 static unsigned long mpx_get_bt_entry_offset_bytes(struct mm_struct *mm,
558 unsigned long addr)
559 {
560 unsigned long bt_table_nr_entries;
561 unsigned long offset = addr;
562
563 if (is_64bit_mm(mm)) {
564 /* Bottom 3 bits are ignored on 64-bit */
565 offset >>= 3;
566 bt_table_nr_entries = MPX_BT_NR_ENTRIES_64;
567 } else {
568 /* Bottom 2 bits are ignored on 32-bit */
569 offset >>= 2;
570 bt_table_nr_entries = MPX_BT_NR_ENTRIES_32;
571 }
572 /*
573 * We know the size of the table in to which we are
574 * indexing, and we have eliminated all the low bits
575 * which are ignored for indexing.
576 *
577 * Mask out all the high bits which we do not need
578 * to index in to the table. Note that the tables
579 * are always powers of two so this gives us a proper
580 * mask.
581 */
582 offset &= (bt_table_nr_entries-1);
583 /*
584 * We now have an entry offset in terms of *entries* in
585 * the table. We need to scale it back up to bytes.
586 */
587 offset *= bt_entry_size_bytes(mm);
588 return offset;
589 }
590
591 /*
592 * How much virtual address space does a single bounds
593 * directory entry cover?
594 *
595 * Note, we need a long long because 4GB doesn't fit in
596 * to a long on 32-bit.
597 */
598 static inline unsigned long bd_entry_virt_space(struct mm_struct *mm)
599 {
600 unsigned long long virt_space;
601 unsigned long long GB = (1ULL << 30);
602
603 /*
604 * This covers 32-bit emulation as well as 32-bit kernels
605 * running on 64-bit hardware.
606 */
607 if (!is_64bit_mm(mm))
608 return (4ULL * GB) / MPX_BD_NR_ENTRIES_32;
609
610 /*
611 * 'x86_virt_bits' returns what the hardware is capable
612 * of, and returns the full >32-bit address space when
613 * running 32-bit kernels on 64-bit hardware.
614 */
615 virt_space = (1ULL << boot_cpu_data.x86_virt_bits);
616 return virt_space / MPX_BD_NR_ENTRIES_64;
617 }
618
619 /*
620 * Free the backing physical pages of bounds table 'bt_addr'.
621 * Assume start...end is within that bounds table.
622 */
623 static noinline int zap_bt_entries_mapping(struct mm_struct *mm,
624 unsigned long bt_addr,
625 unsigned long start_mapping, unsigned long end_mapping)
626 {
627 struct vm_area_struct *vma;
628 unsigned long addr, len;
629 unsigned long start;
630 unsigned long end;
631
632 /*
633 * if we 'end' on a boundary, the offset will be 0 which
634 * is not what we want. Back it up a byte to get the
635 * last bt entry. Then once we have the entry itself,
636 * move 'end' back up by the table entry size.
637 */
638 start = bt_addr + mpx_get_bt_entry_offset_bytes(mm, start_mapping);
639 end = bt_addr + mpx_get_bt_entry_offset_bytes(mm, end_mapping - 1);
640 /*
641 * Move end back up by one entry. Among other things
642 * this ensures that it remains page-aligned and does
643 * not screw up zap_page_range()
644 */
645 end += bt_entry_size_bytes(mm);
646
647 /*
648 * Find the first overlapping vma. If vma->vm_start > start, there
649 * will be a hole in the bounds table. This -EINVAL return will
650 * cause a SIGSEGV.
651 */
652 vma = find_vma(mm, start);
653 if (!vma || vma->vm_start > start)
654 return -EINVAL;
655
656 /*
657 * A NUMA policy on a VM_MPX VMA could cause this bounds table to
658 * be split. So we need to look across the entire 'start -> end'
659 * range of this bounds table, find all of the VM_MPX VMAs, and
660 * zap only those.
661 */
662 addr = start;
663 while (vma && vma->vm_start < end) {
664 /*
665 * We followed a bounds directory entry down
666 * here. If we find a non-MPX VMA, that's bad,
667 * so stop immediately and return an error. This
668 * probably results in a SIGSEGV.
669 */
670 if (!(vma->vm_flags & VM_MPX))
671 return -EINVAL;
672
673 len = min(vma->vm_end, end) - addr;
674 zap_page_range(vma, addr, len);
675 trace_mpx_unmap_zap(addr, addr+len);
676
677 vma = vma->vm_next;
678 addr = vma->vm_start;
679 }
680 return 0;
681 }
682
683 static unsigned long mpx_get_bd_entry_offset(struct mm_struct *mm,
684 unsigned long addr)
685 {
686 /*
687 * There are several ways to derive the bd offsets. We
688 * use the following approach here:
689 * 1. We know the size of the virtual address space
690 * 2. We know the number of entries in a bounds table
691 * 3. We know that each entry covers a fixed amount of
692 * virtual address space.
693 * So, we can just divide the virtual address by the
694 * virtual space used by one entry to determine which
695 * entry "controls" the given virtual address.
696 */
697 if (is_64bit_mm(mm)) {
698 int bd_entry_size = 8; /* 64-bit pointer */
699 /*
700 * Take the 64-bit addressing hole in to account.
701 */
702 addr &= ((1UL << boot_cpu_data.x86_virt_bits) - 1);
703 return (addr / bd_entry_virt_space(mm)) * bd_entry_size;
704 } else {
705 int bd_entry_size = 4; /* 32-bit pointer */
706 /*
707 * 32-bit has no hole so this case needs no mask
708 */
709 return (addr / bd_entry_virt_space(mm)) * bd_entry_size;
710 }
711 /*
712 * The two return calls above are exact copies. If we
713 * pull out a single copy and put it in here, gcc won't
714 * realize that we're doing a power-of-2 divide and use
715 * shifts. It uses a real divide. If we put them up
716 * there, it manages to figure it out (gcc 4.8.3).
717 */
718 }
719
720 static int unmap_entire_bt(struct mm_struct *mm,
721 long __user *bd_entry, unsigned long bt_addr)
722 {
723 unsigned long expected_old_val = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
724 unsigned long uninitialized_var(actual_old_val);
725 int ret;
726
727 while (1) {
728 int need_write = 1;
729 unsigned long cleared_bd_entry = 0;
730
731 pagefault_disable();
732 ret = mpx_cmpxchg_bd_entry(mm, &actual_old_val,
733 bd_entry, expected_old_val, cleared_bd_entry);
734 pagefault_enable();
735 if (!ret)
736 break;
737 if (ret == -EFAULT)
738 ret = mpx_resolve_fault(bd_entry, need_write);
739 /*
740 * If we could not resolve the fault, consider it
741 * userspace's fault and error out.
742 */
743 if (ret)
744 return ret;
745 }
746 /*
747 * The cmpxchg was performed, check the results.
748 */
749 if (actual_old_val != expected_old_val) {
750 /*
751 * Someone else raced with us to unmap the table.
752 * That is OK, since we were both trying to do
753 * the same thing. Declare success.
754 */
755 if (!actual_old_val)
756 return 0;
757 /*
758 * Something messed with the bounds directory
759 * entry. We hold mmap_sem for read or write
760 * here, so it could not be a _new_ bounds table
761 * that someone just allocated. Something is
762 * wrong, so pass up the error and SIGSEGV.
763 */
764 return -EINVAL;
765 }
766 /*
767 * Note, we are likely being called under do_munmap() already. To
768 * avoid recursion, do_munmap() will check whether it comes
769 * from one bounds table through VM_MPX flag.
770 */
771 return do_munmap(mm, bt_addr, mpx_bt_size_bytes(mm), NULL);
772 }
773
774 static int try_unmap_single_bt(struct mm_struct *mm,
775 unsigned long start, unsigned long end)
776 {
777 struct vm_area_struct *next;
778 struct vm_area_struct *prev;
779 /*
780 * "bta" == Bounds Table Area: the area controlled by the
781 * bounds table that we are unmapping.
782 */
783 unsigned long bta_start_vaddr = start & ~(bd_entry_virt_space(mm)-1);
784 unsigned long bta_end_vaddr = bta_start_vaddr + bd_entry_virt_space(mm);
785 unsigned long uninitialized_var(bt_addr);
786 void __user *bde_vaddr;
787 int ret;
788 /*
789 * We already unlinked the VMAs from the mm's rbtree so 'start'
790 * is guaranteed to be in a hole. This gets us the first VMA
791 * before the hole in to 'prev' and the next VMA after the hole
792 * in to 'next'.
793 */
794 next = find_vma_prev(mm, start, &prev);
795 /*
796 * Do not count other MPX bounds table VMAs as neighbors.
797 * Although theoretically possible, we do not allow bounds
798 * tables for bounds tables so our heads do not explode.
799 * If we count them as neighbors here, we may end up with
800 * lots of tables even though we have no actual table
801 * entries in use.
802 */
803 while (next && (next->vm_flags & VM_MPX))
804 next = next->vm_next;
805 while (prev && (prev->vm_flags & VM_MPX))
806 prev = prev->vm_prev;
807 /*
808 * We know 'start' and 'end' lie within an area controlled
809 * by a single bounds table. See if there are any other
810 * VMAs controlled by that bounds table. If there are not
811 * then we can "expand" the are we are unmapping to possibly
812 * cover the entire table.
813 */
814 next = find_vma_prev(mm, start, &prev);
815 if ((!prev || prev->vm_end <= bta_start_vaddr) &&
816 (!next || next->vm_start >= bta_end_vaddr)) {
817 /*
818 * No neighbor VMAs controlled by same bounds
819 * table. Try to unmap the whole thing
820 */
821 start = bta_start_vaddr;
822 end = bta_end_vaddr;
823 }
824
825 bde_vaddr = mm->context.bd_addr + mpx_get_bd_entry_offset(mm, start);
826 ret = get_bt_addr(mm, bde_vaddr, &bt_addr);
827 /*
828 * No bounds table there, so nothing to unmap.
829 */
830 if (ret == -ENOENT) {
831 ret = 0;
832 return 0;
833 }
834 if (ret)
835 return ret;
836 /*
837 * We are unmapping an entire table. Either because the
838 * unmap that started this whole process was large enough
839 * to cover an entire table, or that the unmap was small
840 * but was the area covered by a bounds table.
841 */
842 if ((start == bta_start_vaddr) &&
843 (end == bta_end_vaddr))
844 return unmap_entire_bt(mm, bde_vaddr, bt_addr);
845 return zap_bt_entries_mapping(mm, bt_addr, start, end);
846 }
847
848 static int mpx_unmap_tables(struct mm_struct *mm,
849 unsigned long start, unsigned long end)
850 {
851 unsigned long one_unmap_start;
852 trace_mpx_unmap_search(start, end);
853
854 one_unmap_start = start;
855 while (one_unmap_start < end) {
856 int ret;
857 unsigned long next_unmap_start = ALIGN(one_unmap_start+1,
858 bd_entry_virt_space(mm));
859 unsigned long one_unmap_end = end;
860 /*
861 * if the end is beyond the current bounds table,
862 * move it back so we only deal with a single one
863 * at a time
864 */
865 if (one_unmap_end > next_unmap_start)
866 one_unmap_end = next_unmap_start;
867 ret = try_unmap_single_bt(mm, one_unmap_start, one_unmap_end);
868 if (ret)
869 return ret;
870
871 one_unmap_start = next_unmap_start;
872 }
873 return 0;
874 }
875
876 /*
877 * Free unused bounds tables covered in a virtual address region being
878 * munmap()ed. Assume end > start.
879 *
880 * This function will be called by do_munmap(), and the VMAs covering
881 * the virtual address region start...end have already been split if
882 * necessary, and the 'vma' is the first vma in this range (start -> end).
883 */
884 void mpx_notify_unmap(struct mm_struct *mm, unsigned long start,
885 unsigned long end)
886 {
887 struct vm_area_struct *vma;
888 int ret;
889
890 /*
891 * Refuse to do anything unless userspace has asked
892 * the kernel to help manage the bounds tables,
893 */
894 if (!kernel_managing_mpx_tables(current->mm))
895 return;
896 /*
897 * This will look across the entire 'start -> end' range,
898 * and find all of the non-VM_MPX VMAs.
899 *
900 * To avoid recursion, if a VM_MPX vma is found in the range
901 * (start->end), we will not continue follow-up work. This
902 * recursion represents having bounds tables for bounds tables,
903 * which should not occur normally. Being strict about it here
904 * helps ensure that we do not have an exploitable stack overflow.
905 */
906 vma = find_vma(mm, start);
907 while (vma && vma->vm_start < end) {
908 if (vma->vm_flags & VM_MPX)
909 return;
910 vma = vma->vm_next;
911 }
912
913 ret = mpx_unmap_tables(mm, start, end);
914 if (ret)
915 force_sig(SIGSEGV);
916 }
917
918 /* MPX cannot handle addresses above 47 bits yet. */
919 unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len,
920 unsigned long flags)
921 {
922 if (!kernel_managing_mpx_tables(current->mm))
923 return addr;
924 if (addr + len <= DEFAULT_MAP_WINDOW)
925 return addr;
926 if (flags & MAP_FIXED)
927 return -ENOMEM;
928
929 /*
930 * Requested len is larger than the whole area we're allowed to map in.
931 * Resetting hinting address wouldn't do much good -- fail early.
932 */
933 if (len > DEFAULT_MAP_WINDOW)
934 return -ENOMEM;
935
936 /* Look for unmap area within DEFAULT_MAP_WINDOW */
937 return 0;
938 }