linux-stable/mm/mincore.c
Jiri Kosina 134fca9063 mm/mincore.c: make mincore() more conservative
The semantics of what mincore() considers to be resident is not
completely clear, but Linux has always (since 2.3.52, which is when
mincore() was initially done) treated it as "page is available in page
cache".

That's potentially a problem, as that [in]directly exposes
meta-information about pagecache / memory mapping state even about
memory not strictly belonging to the process executing the syscall,
opening possibilities for sidechannel attacks.

Change the semantics of mincore() so that it only reveals pagecache
information for non-anonymous mappings that belog to files that the
calling process could (if it tried to) successfully open for writing;
otherwise we'd be including shared non-exclusive mappings, which

 - is the sidechannel

 - is not the usecase for mincore(), as that's primarily used for data,
   not (shared) text

[jkosina@suse.cz: v2]
  Link: http://lkml.kernel.org/r/20190312141708.6652-2-vbabka@suse.cz
[mhocko@suse.com: restructure can_do_mincore() conditions]
Link: http://lkml.kernel.org/r/nycvar.YFH.7.76.1903062342020.19912@cbobk.fhfr.pm
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Josh Snyder <joshs@netflix.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Originally-by: Linus Torvalds <torvalds@linux-foundation.org>
Originally-by: Dominique Martinet <asmadeus@codewreck.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Kevin Easton <kevin@guarana.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Cyril Hrubis <chrubis@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Daniel Gruss <daniel@gruss.cc>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 19:52:48 -07:00

294 lines
7.3 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/mm/mincore.c
*
* Copyright (C) 1994-2006 Linus Torvalds
*/
/*
* The mincore() system call.
*/
#include <linux/pagemap.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
#include <linux/hugetlb.h>
#include <linux/uaccess.h>
#include <asm/pgtable.h>
static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
unsigned long end, struct mm_walk *walk)
{
#ifdef CONFIG_HUGETLB_PAGE
unsigned char present;
unsigned char *vec = walk->private;
/*
* Hugepages under user process are always in RAM and never
* swapped out, but theoretically it needs to be checked.
*/
present = pte && !huge_pte_none(huge_ptep_get(pte));
for (; addr != end; vec++, addr += PAGE_SIZE)
*vec = present;
walk->private = vec;
#else
BUG();
#endif
return 0;
}
/*
* Later we can get more picky about what "in core" means precisely.
* For now, simply check to see if the page is in the page cache,
* and is up to date; i.e. that no page-in operation would be required
* at this time if an application were to map and access this page.
*/
static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
{
unsigned char present = 0;
struct page *page;
/*
* When tmpfs swaps out a page from a file, any process mapping that
* file will not get a swp_entry_t in its pte, but rather it is like
* any other file mapping (ie. marked !present and faulted in with
* tmpfs's .fault). So swapped out tmpfs mappings are tested here.
*/
#ifdef CONFIG_SWAP
if (shmem_mapping(mapping)) {
page = find_get_entry(mapping, pgoff);
/*
* shmem/tmpfs may return swap: account for swapcache
* page too.
*/
if (xa_is_value(page)) {
swp_entry_t swp = radix_to_swp_entry(page);
page = find_get_page(swap_address_space(swp),
swp_offset(swp));
}
} else
page = find_get_page(mapping, pgoff);
#else
page = find_get_page(mapping, pgoff);
#endif
if (page) {
present = PageUptodate(page);
put_page(page);
}
return present;
}
static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
struct vm_area_struct *vma, unsigned char *vec)
{
unsigned long nr = (end - addr) >> PAGE_SHIFT;
int i;
if (vma->vm_file) {
pgoff_t pgoff;
pgoff = linear_page_index(vma, addr);
for (i = 0; i < nr; i++, pgoff++)
vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
} else {
for (i = 0; i < nr; i++)
vec[i] = 0;
}
return nr;
}
static int mincore_unmapped_range(unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
walk->private += __mincore_unmapped_range(addr, end,
walk->vma, walk->private);
return 0;
}
static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
spinlock_t *ptl;
struct vm_area_struct *vma = walk->vma;
pte_t *ptep;
unsigned char *vec = walk->private;
int nr = (end - addr) >> PAGE_SHIFT;
ptl = pmd_trans_huge_lock(pmd, vma);
if (ptl) {
memset(vec, 1, nr);
spin_unlock(ptl);
goto out;
}
if (pmd_trans_unstable(pmd)) {
__mincore_unmapped_range(addr, end, vma, vec);
goto out;
}
ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
for (; addr != end; ptep++, addr += PAGE_SIZE) {
pte_t pte = *ptep;
if (pte_none(pte))
__mincore_unmapped_range(addr, addr + PAGE_SIZE,
vma, vec);
else if (pte_present(pte))
*vec = 1;
else { /* pte is a swap entry */
swp_entry_t entry = pte_to_swp_entry(pte);
if (non_swap_entry(entry)) {
/*
* migration or hwpoison entries are always
* uptodate
*/
*vec = 1;
} else {
#ifdef CONFIG_SWAP
*vec = mincore_page(swap_address_space(entry),
swp_offset(entry));
#else
WARN_ON(1);
*vec = 1;
#endif
}
}
vec++;
}
pte_unmap_unlock(ptep - 1, ptl);
out:
walk->private += nr;
cond_resched();
return 0;
}
static inline bool can_do_mincore(struct vm_area_struct *vma)
{
if (vma_is_anonymous(vma))
return true;
if (!vma->vm_file)
return false;
/*
* Reveal pagecache information only for non-anonymous mappings that
* correspond to the files the calling process could (if tried) open
* for writing; otherwise we'd be including shared non-exclusive
* mappings, which opens a side channel.
*/
return inode_owner_or_capable(file_inode(vma->vm_file)) ||
inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
}
/*
* Do a chunk of "sys_mincore()". We've already checked
* all the arguments, we hold the mmap semaphore: we should
* just return the amount of info we're asked for.
*/
static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
{
struct vm_area_struct *vma;
unsigned long end;
int err;
struct mm_walk mincore_walk = {
.pmd_entry = mincore_pte_range,
.pte_hole = mincore_unmapped_range,
.hugetlb_entry = mincore_hugetlb,
.private = vec,
};
vma = find_vma(current->mm, addr);
if (!vma || addr < vma->vm_start)
return -ENOMEM;
end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
if (!can_do_mincore(vma)) {
unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE);
memset(vec, 1, pages);
return pages;
}
mincore_walk.mm = vma->vm_mm;
err = walk_page_range(addr, end, &mincore_walk);
if (err < 0)
return err;
return (end - addr) >> PAGE_SHIFT;
}
/*
* The mincore(2) system call.
*
* mincore() returns the memory residency status of the pages in the
* current process's address space specified by [addr, addr + len).
* The status is returned in a vector of bytes. The least significant
* bit of each byte is 1 if the referenced page is in memory, otherwise
* it is zero.
*
* Because the status of a page can change after mincore() checks it
* but before it returns to the application, the returned vector may
* contain stale information. Only locked pages are guaranteed to
* remain in memory.
*
* return values:
* zero - success
* -EFAULT - vec points to an illegal address
* -EINVAL - addr is not a multiple of PAGE_SIZE
* -ENOMEM - Addresses in the range [addr, addr + len] are
* invalid for the address space of this process, or
* specify one or more pages which are not currently
* mapped
* -EAGAIN - A kernel resource was temporarily unavailable.
*/
SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
unsigned char __user *, vec)
{
long retval;
unsigned long pages;
unsigned char *tmp;
/* Check the start address: needs to be page-aligned.. */
if (start & ~PAGE_MASK)
return -EINVAL;
/* ..and we need to be passed a valid user-space range */
if (!access_ok((void __user *) start, len))
return -ENOMEM;
/* This also avoids any overflows on PAGE_ALIGN */
pages = len >> PAGE_SHIFT;
pages += (offset_in_page(len)) != 0;
if (!access_ok(vec, pages))
return -EFAULT;
tmp = (void *) __get_free_page(GFP_USER);
if (!tmp)
return -EAGAIN;
retval = 0;
while (pages) {
/*
* Do at most PAGE_SIZE entries per iteration, due to
* the temporary buffer size.
*/
down_read(&current->mm->mmap_sem);
retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
up_read(&current->mm->mmap_sem);
if (retval <= 0)
break;
if (copy_to_user(vec, tmp, retval)) {
retval = -EFAULT;
break;
}
pages -= retval;
vec += retval;
start += retval << PAGE_SHIFT;
retval = 0;
}
free_page((unsigned long) tmp);
return retval;
}