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