mm/mincore.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *      linux/mm/mincore.c
   4  *
   5  * Copyright (C) 1994-2006  Linus Torvalds
   6  */
   7
   8 /*
   9  * The mincore() system call.
  10  */
  11 #include <linux/pagemap.h>
  12 #include <linux/gfp.h>
  13 #include <linux/pagewalk.h>
  14 #include <linux/mman.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/swap.h>
  17 #include <linux/swapops.h>
  18 #include <linux/shmem_fs.h>
  19 #include <linux/hugetlb.h>
  20 #include <linux/pgtable.h>
  21
  22 #include <linux/uaccess.h>
  23 #include "swap.h"
  24
  25 static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
  26                         unsigned long end, struct mm_walk *walk)
  27 {
  28 #ifdef CONFIG_HUGETLB_PAGE
  29         unsigned char present;
  30         unsigned char *vec = walk->private;
  31
  32         /*
  33          * Hugepages under user process are always in RAM and never
  34          * swapped out, but theoretically it needs to be checked.
  35          */
  36         present = pte && !huge_pte_none_mostly(huge_ptep_get(walk->mm, addr, pte));
  37         for (; addr != end; vec++, addr += PAGE_SIZE)
  38                 *vec = present;
  39         walk->private = vec;
  40 #else
  41         BUG();
  42 #endif
  43         return 0;
  44 }
  45
  46 /*
  47  * Later we can get more picky about what "in core" means precisely.
  48  * For now, simply check to see if the page is in the page cache,
  49  * and is up to date; i.e. that no page-in operation would be required
  50  * at this time if an application were to map and access this page.
  51  */
  52 static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
  53 {
  54         unsigned char present = 0;
  55         struct folio *folio;
  56
  57         /*
  58          * When tmpfs swaps out a page from a file, any process mapping that
  59          * file will not get a swp_entry_t in its pte, but rather it is like
  60          * any other file mapping (ie. marked !present and faulted in with
  61          * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
  62          */
  63         folio = filemap_get_incore_folio(mapping, index);
  64         if (!IS_ERR(folio)) {
  65                 present = folio_test_uptodate(folio);
  66                 folio_put(folio);
  67         }
  68
  69         return present;
  70 }
  71
  72 static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
  73                                 struct vm_area_struct *vma, unsigned char *vec)
  74 {
  75         unsigned long nr = (end - addr) >> PAGE_SHIFT;
  76         int i;
  77
  78         if (vma->vm_file) {
  79                 pgoff_t pgoff;
  80
  81                 pgoff = linear_page_index(vma, addr);
  82                 for (i = 0; i < nr; i++, pgoff++)
  83                         vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
  84         } else {
  85                 for (i = 0; i < nr; i++)
  86                         vec[i] = 0;
  87         }
  88         return nr;
  89 }
  90
  91 static int mincore_unmapped_range(unsigned long addr, unsigned long end,
  92                                    __always_unused int depth,
  93                                    struct mm_walk *walk)
  94 {
  95         walk->private += __mincore_unmapped_range(addr, end,
  96                                                   walk->vma, walk->private);
  97         return 0;
  98 }
  99
 100 static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 101                         struct mm_walk *walk)
 102 {
 103         spinlock_t *ptl;
 104         struct vm_area_struct *vma = walk->vma;
 105         pte_t *ptep;
 106         unsigned char *vec = walk->private;
 107         int nr = (end - addr) >> PAGE_SHIFT;
 108
 109         ptl = pmd_trans_huge_lock(pmd, vma);
 110         if (ptl) {
 111                 memset(vec, 1, nr);
 112                 spin_unlock(ptl);
 113                 goto out;
 114         }
 115
 116         ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 117         if (!ptep) {
 118                 walk->action = ACTION_AGAIN;
 119                 return 0;
 120         }
 121         for (; addr != end; ptep++, addr += PAGE_SIZE) {
 122                 pte_t pte = ptep_get(ptep);
 123
 124                 /* We need to do cache lookup too for pte markers */
 125                 if (pte_none_mostly(pte))
 126                         __mincore_unmapped_range(addr, addr + PAGE_SIZE,
 127                                                  vma, vec);
 128                 else if (pte_present(pte))
 129                         *vec = 1;
 130                 else { /* pte is a swap entry */
 131                         swp_entry_t entry = pte_to_swp_entry(pte);
 132
 133                         if (non_swap_entry(entry)) {
 134                                 /*
 135                                  * migration or hwpoison entries are always
 136                                  * uptodate
 137                                  */
 138                                 *vec = 1;
 139                         } else {
 140 #ifdef CONFIG_SWAP
 141                                 *vec = mincore_page(swap_address_space(entry),
 142                                                     swap_cache_index(entry));
 143 #else
 144                                 WARN_ON(1);
 145                                 *vec = 1;
 146 #endif
 147                         }
 148                 }
 149                 vec++;
 150         }
 151         pte_unmap_unlock(ptep - 1, ptl);
 152 out:
 153         walk->private += nr;
 154         cond_resched();
 155         return 0;
 156 }
 157
 158 static inline bool can_do_mincore(struct vm_area_struct *vma)
 159 {
 160         if (vma_is_anonymous(vma))
 161                 return true;
 162         if (!vma->vm_file)
 163                 return false;
 164         /*
 165          * Reveal pagecache information only for non-anonymous mappings that
 166          * correspond to the files the calling process could (if tried) open
 167          * for writing; otherwise we'd be including shared non-exclusive
 168          * mappings, which opens a side channel.
 169          */
 170         return inode_owner_or_capable(&nop_mnt_idmap,
 171                                       file_inode(vma->vm_file)) ||
 172                file_permission(vma->vm_file, MAY_WRITE) == 0;
 173 }
 174
 175 static const struct mm_walk_ops mincore_walk_ops = {
 176         .pmd_entry              = mincore_pte_range,
 177         .pte_hole               = mincore_unmapped_range,
 178         .hugetlb_entry          = mincore_hugetlb,
 179         .walk_lock              = PGWALK_RDLOCK,
 180 };
 181
 182 /*
 183  * Do a chunk of "sys_mincore()". We've already checked
 184  * all the arguments, we hold the mmap semaphore: we should
 185  * just return the amount of info we're asked for.
 186  */
 187 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
 188 {
 189         struct vm_area_struct *vma;
 190         unsigned long end;
 191         int err;
 192
 193         vma = vma_lookup(current->mm, addr);
 194         if (!vma)
 195                 return -ENOMEM;
 196         end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
 197         if (!can_do_mincore(vma)) {
 198                 unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE);
 199                 memset(vec, 1, pages);
 200                 return pages;
 201         }
 202         err = walk_page_range(vma->vm_mm, addr, end, &mincore_walk_ops, vec);
 203         if (err < 0)
 204                 return err;
 205         return (end - addr) >> PAGE_SHIFT;
 206 }
 207
 208 /*
 209  * The mincore(2) system call.
 210  *
 211  * mincore() returns the memory residency status of the pages in the
 212  * current process's address space specified by [addr, addr + len).
 213  * The status is returned in a vector of bytes.  The least significant
 214  * bit of each byte is 1 if the referenced page is in memory, otherwise
 215  * it is zero.
 216  *
 217  * Because the status of a page can change after mincore() checks it
 218  * but before it returns to the application, the returned vector may
 219  * contain stale information.  Only locked pages are guaranteed to
 220  * remain in memory.
 221  *
 222  * return values:
 223  *  zero    - success
 224  *  -EFAULT - vec points to an illegal address
 225  *  -EINVAL - addr is not a multiple of PAGE_SIZE
 226  *  -ENOMEM - Addresses in the range [addr, addr + len] are
 227  *              invalid for the address space of this process, or
 228  *              specify one or more pages which are not currently
 229  *              mapped
 230  *  -EAGAIN - A kernel resource was temporarily unavailable.
 231  */
 232 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
 233                 unsigned char __user *, vec)
 234 {
 235         long retval;
 236         unsigned long pages;
 237         unsigned char *tmp;
 238
 239         start = untagged_addr(start);
 240
 241         /* Check the start address: needs to be page-aligned.. */
 242         if (start & ~PAGE_MASK)
 243                 return -EINVAL;
 244
 245         /* ..and we need to be passed a valid user-space range */
 246         if (!access_ok((void __user *) start, len))
 247                 return -ENOMEM;
 248
 249         /* This also avoids any overflows on PAGE_ALIGN */
 250         pages = len >> PAGE_SHIFT;
 251         pages += (offset_in_page(len)) != 0;
 252
 253         if (!access_ok(vec, pages))
 254                 return -EFAULT;
 255
 256         tmp = (void *) __get_free_page(GFP_USER);
 257         if (!tmp)
 258                 return -EAGAIN;
 259
 260         retval = 0;
 261         while (pages) {
 262                 /*
 263                  * Do at most PAGE_SIZE entries per iteration, due to
 264                  * the temporary buffer size.
 265                  */
 266                 mmap_read_lock(current->mm);
 267                 retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
 268                 mmap_read_unlock(current->mm);
 269
 270                 if (retval <= 0)
 271                         break;
 272                 if (copy_to_user(vec, tmp, retval)) {
 273                         retval = -EFAULT;
 274                         break;
 275                 }
 276                 pages -= retval;
 277                 vec += retval;
 278                 start += retval << PAGE_SHIFT;
 279                 retval = 0;
 280         }
 281         free_page((unsigned long) tmp);
 282         return retval;
 283 }