linux/mm/mlock.c
Linus Torvalds d7824370e2 mm: fix up some user-visible effects of the stack guard page
This commit makes the stack guard page somewhat less visible to user
space. It does this by:

 - not showing the guard page in /proc/<pid>/maps

   It looks like lvm-tools will actually read /proc/self/maps to figure
   out where all its mappings are, and effectively do a specialized
   "mlockall()" in user space.  By not showing the guard page as part of
   the mapping (by just adding PAGE_SIZE to the start for grows-up
   pages), lvm-tools ends up not being aware of it.

 - by also teaching the _real_ mlock() functionality not to try to lock
   the guard page.

   That would just expand the mapping down to create a new guard page,
   so there really is no point in trying to lock it in place.

It would perhaps be nice to show the guard page specially in
/proc/<pid>/maps (or at least mark grow-down segments some way), but
let's not open ourselves up to more breakage by user space from programs
that depends on the exact deails of the 'maps' file.

Special thanks to Henrique de Moraes Holschuh for diving into lvm-tools
source code to see what was going on with the whole new warning.

Reported-and-tested-by: François Valenduc <francois.valenduc@tvcablenet.be
Reported-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-08-15 11:35:52 -07:00

618 lines
15 KiB
C

/*
* linux/mm/mlock.c
*
* (C) Copyright 1995 Linus Torvalds
* (C) Copyright 2002 Christoph Hellwig
*/
#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>
#include "internal.h"
int can_do_mlock(void)
{
if (capable(CAP_IPC_LOCK))
return 1;
if (rlimit(RLIMIT_MEMLOCK) != 0)
return 1;
return 0;
}
EXPORT_SYMBOL(can_do_mlock);
/*
* Mlocked pages are marked with PageMlocked() flag for efficient testing
* in vmscan and, possibly, the fault path; and to support semi-accurate
* statistics.
*
* An mlocked page [PageMlocked(page)] is unevictable. As such, it will
* be placed on the LRU "unevictable" list, rather than the [in]active lists.
* The unevictable list is an LRU sibling list to the [in]active lists.
* PageUnevictable is set to indicate the unevictable state.
*
* When lazy mlocking via vmscan, it is important to ensure that the
* vma's VM_LOCKED status is not concurrently being modified, otherwise we
* may have mlocked a page that is being munlocked. So lazy mlock must take
* the mmap_sem for read, and verify that the vma really is locked
* (see mm/rmap.c).
*/
/*
* LRU accounting for clear_page_mlock()
*/
void __clear_page_mlock(struct page *page)
{
VM_BUG_ON(!PageLocked(page));
if (!page->mapping) { /* truncated ? */
return;
}
dec_zone_page_state(page, NR_MLOCK);
count_vm_event(UNEVICTABLE_PGCLEARED);
if (!isolate_lru_page(page)) {
putback_lru_page(page);
} else {
/*
* We lost the race. the page already moved to evictable list.
*/
if (PageUnevictable(page))
count_vm_event(UNEVICTABLE_PGSTRANDED);
}
}
/*
* Mark page as mlocked if not already.
* If page on LRU, isolate and putback to move to unevictable list.
*/
void mlock_vma_page(struct page *page)
{
BUG_ON(!PageLocked(page));
if (!TestSetPageMlocked(page)) {
inc_zone_page_state(page, NR_MLOCK);
count_vm_event(UNEVICTABLE_PGMLOCKED);
if (!isolate_lru_page(page))
putback_lru_page(page);
}
}
/**
* munlock_vma_page - munlock a vma page
* @page - page to be unlocked
*
* called from munlock()/munmap() path with page supposedly on the LRU.
* When we munlock a page, because the vma where we found the page is being
* munlock()ed or munmap()ed, we want to check whether other vmas hold the
* page locked so that we can leave it on the unevictable lru list and not
* bother vmscan with it. However, to walk the page's rmap list in
* try_to_munlock() we must isolate the page from the LRU. If some other
* task has removed the page from the LRU, we won't be able to do that.
* So we clear the PageMlocked as we might not get another chance. If we
* can't isolate the page, we leave it for putback_lru_page() and vmscan
* [page_referenced()/try_to_unmap()] to deal with.
*/
void munlock_vma_page(struct page *page)
{
BUG_ON(!PageLocked(page));
if (TestClearPageMlocked(page)) {
dec_zone_page_state(page, NR_MLOCK);
if (!isolate_lru_page(page)) {
int ret = try_to_munlock(page);
/*
* did try_to_unlock() succeed or punt?
*/
if (ret != SWAP_MLOCK)
count_vm_event(UNEVICTABLE_PGMUNLOCKED);
putback_lru_page(page);
} else {
/*
* Some other task has removed the page from the LRU.
* putback_lru_page() will take care of removing the
* page from the unevictable list, if necessary.
* vmscan [page_referenced()] will move the page back
* to the unevictable list if some other vma has it
* mlocked.
*/
if (PageUnevictable(page))
count_vm_event(UNEVICTABLE_PGSTRANDED);
else
count_vm_event(UNEVICTABLE_PGMUNLOCKED);
}
}
}
/**
* __mlock_vma_pages_range() - mlock a range of pages in the vma.
* @vma: target vma
* @start: start address
* @end: end address
*
* This takes care of making the pages present too.
*
* return 0 on success, negative error code on error.
*
* vma->vm_mm->mmap_sem must be held for at least read.
*/
static long __mlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = start;
struct page *pages[16]; /* 16 gives a reasonable batch */
int nr_pages = (end - start) / PAGE_SIZE;
int ret = 0;
int gup_flags;
VM_BUG_ON(start & ~PAGE_MASK);
VM_BUG_ON(end & ~PAGE_MASK);
VM_BUG_ON(start < vma->vm_start);
VM_BUG_ON(end > vma->vm_end);
VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
gup_flags = FOLL_TOUCH | FOLL_GET;
if (vma->vm_flags & VM_WRITE)
gup_flags |= FOLL_WRITE;
/* We don't try to access the guard page of a stack vma */
if (vma->vm_flags & VM_GROWSDOWN) {
if (start == vma->vm_start) {
start += PAGE_SIZE;
nr_pages--;
}
}
while (nr_pages > 0) {
int i;
cond_resched();
/*
* get_user_pages makes pages present if we are
* setting mlock. and this extra reference count will
* disable migration of this page. However, page may
* still be truncated out from under us.
*/
ret = __get_user_pages(current, mm, addr,
min_t(int, nr_pages, ARRAY_SIZE(pages)),
gup_flags, pages, NULL);
/*
* This can happen for, e.g., VM_NONLINEAR regions before
* a page has been allocated and mapped at a given offset,
* or for addresses that map beyond end of a file.
* We'll mlock the pages if/when they get faulted in.
*/
if (ret < 0)
break;
lru_add_drain(); /* push cached pages to LRU */
for (i = 0; i < ret; i++) {
struct page *page = pages[i];
if (page->mapping) {
/*
* That preliminary check is mainly to avoid
* the pointless overhead of lock_page on the
* ZERO_PAGE: which might bounce very badly if
* there is contention. However, we're still
* dirtying its cacheline with get/put_page:
* we'll add another __get_user_pages flag to
* avoid it if that case turns out to matter.
*/
lock_page(page);
/*
* Because we lock page here and migration is
* blocked by the elevated reference, we need
* only check for file-cache page truncation.
*/
if (page->mapping)
mlock_vma_page(page);
unlock_page(page);
}
put_page(page); /* ref from get_user_pages() */
}
addr += ret * PAGE_SIZE;
nr_pages -= ret;
ret = 0;
}
return ret; /* 0 or negative error code */
}
/*
* convert get_user_pages() return value to posix mlock() error
*/
static int __mlock_posix_error_return(long retval)
{
if (retval == -EFAULT)
retval = -ENOMEM;
else if (retval == -ENOMEM)
retval = -EAGAIN;
return retval;
}
/**
* mlock_vma_pages_range() - mlock pages in specified vma range.
* @vma - the vma containing the specfied address range
* @start - starting address in @vma to mlock
* @end - end address [+1] in @vma to mlock
*
* For mmap()/mremap()/expansion of mlocked vma.
*
* return 0 on success for "normal" vmas.
*
* return number of pages [> 0] to be removed from locked_vm on success
* of "special" vmas.
*/
long mlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
int nr_pages = (end - start) / PAGE_SIZE;
BUG_ON(!(vma->vm_flags & VM_LOCKED));
/*
* filter unlockable vmas
*/
if (vma->vm_flags & (VM_IO | VM_PFNMAP))
goto no_mlock;
if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
is_vm_hugetlb_page(vma) ||
vma == get_gate_vma(current))) {
__mlock_vma_pages_range(vma, start, end);
/* Hide errors from mmap() and other callers */
return 0;
}
/*
* User mapped kernel pages or huge pages:
* make these pages present to populate the ptes, but
* fall thru' to reset VM_LOCKED--no need to unlock, and
* return nr_pages so these don't get counted against task's
* locked limit. huge pages are already counted against
* locked vm limit.
*/
make_pages_present(start, end);
no_mlock:
vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */
return nr_pages; /* error or pages NOT mlocked */
}
/*
* munlock_vma_pages_range() - munlock all pages in the vma range.'
* @vma - vma containing range to be munlock()ed.
* @start - start address in @vma of the range
* @end - end of range in @vma.
*
* For mremap(), munmap() and exit().
*
* Called with @vma VM_LOCKED.
*
* Returns with VM_LOCKED cleared. Callers must be prepared to
* deal with this.
*
* We don't save and restore VM_LOCKED here because pages are
* still on lru. In unmap path, pages might be scanned by reclaim
* and re-mlocked by try_to_{munlock|unmap} before we unmap and
* free them. This will result in freeing mlocked pages.
*/
void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
unsigned long addr;
lru_add_drain();
vma->vm_flags &= ~VM_LOCKED;
for (addr = start; addr < end; addr += PAGE_SIZE) {
struct page *page;
/*
* Although FOLL_DUMP is intended for get_dump_page(),
* it just so happens that its special treatment of the
* ZERO_PAGE (returning an error instead of doing get_page)
* suits munlock very well (and if somehow an abnormal page
* has sneaked into the range, we won't oops here: great).
*/
page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
if (page && !IS_ERR(page)) {
lock_page(page);
/*
* Like in __mlock_vma_pages_range(),
* because we lock page here and migration is
* blocked by the elevated reference, we need
* only check for file-cache page truncation.
*/
if (page->mapping)
munlock_vma_page(page);
unlock_page(page);
put_page(page);
}
cond_resched();
}
}
/*
* mlock_fixup - handle mlock[all]/munlock[all] requests.
*
* Filters out "special" vmas -- VM_LOCKED never gets set for these, and
* munlock is a no-op. However, for some special vmas, we go ahead and
* populate the ptes via make_pages_present().
*
* For vmas that pass the filters, merge/split as appropriate.
*/
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end, unsigned int newflags)
{
struct mm_struct *mm = vma->vm_mm;
pgoff_t pgoff;
int nr_pages;
int ret = 0;
int lock = newflags & VM_LOCKED;
if (newflags == vma->vm_flags ||
(vma->vm_flags & (VM_IO | VM_PFNMAP)))
goto out; /* don't set VM_LOCKED, don't count */
if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
is_vm_hugetlb_page(vma) ||
vma == get_gate_vma(current)) {
if (lock)
make_pages_present(start, end);
goto out; /* don't set VM_LOCKED, don't count */
}
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma));
if (*prev) {
vma = *prev;
goto success;
}
if (start != vma->vm_start) {
ret = split_vma(mm, vma, start, 1);
if (ret)
goto out;
}
if (end != vma->vm_end) {
ret = split_vma(mm, vma, end, 0);
if (ret)
goto out;
}
success:
/*
* Keep track of amount of locked VM.
*/
nr_pages = (end - start) >> PAGE_SHIFT;
if (!lock)
nr_pages = -nr_pages;
mm->locked_vm += nr_pages;
/*
* vm_flags is protected by the mmap_sem held in write mode.
* It's okay if try_to_unmap_one unmaps a page just after we
* set VM_LOCKED, __mlock_vma_pages_range will bring it back.
*/
if (lock) {
vma->vm_flags = newflags;
ret = __mlock_vma_pages_range(vma, start, end);
if (ret < 0)
ret = __mlock_posix_error_return(ret);
} else {
munlock_vma_pages_range(vma, start, end);
}
out:
*prev = vma;
return ret;
}
static int do_mlock(unsigned long start, size_t len, int on)
{
unsigned long nstart, end, tmp;
struct vm_area_struct * vma, * prev;
int error;
len = PAGE_ALIGN(len);
end = start + len;
if (end < start)
return -EINVAL;
if (end == start)
return 0;
vma = find_vma_prev(current->mm, start, &prev);
if (!vma || vma->vm_start > start)
return -ENOMEM;
if (start > vma->vm_start)
prev = vma;
for (nstart = start ; ; ) {
unsigned int newflags;
/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
newflags = vma->vm_flags | VM_LOCKED;
if (!on)
newflags &= ~VM_LOCKED;
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
if (error)
break;
nstart = tmp;
if (nstart < prev->vm_end)
nstart = prev->vm_end;
if (nstart >= end)
break;
vma = prev->vm_next;
if (!vma || vma->vm_start != nstart) {
error = -ENOMEM;
break;
}
}
return error;
}
SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
{
unsigned long locked;
unsigned long lock_limit;
int error = -ENOMEM;
if (!can_do_mlock())
return -EPERM;
lru_add_drain_all(); /* flush pagevec */
down_write(&current->mm->mmap_sem);
len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
start &= PAGE_MASK;
locked = len >> PAGE_SHIFT;
locked += current->mm->locked_vm;
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
/* check against resource limits */
if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
error = do_mlock(start, len, 1);
up_write(&current->mm->mmap_sem);
return error;
}
SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
{
int ret;
down_write(&current->mm->mmap_sem);
len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
start &= PAGE_MASK;
ret = do_mlock(start, len, 0);
up_write(&current->mm->mmap_sem);
return ret;
}
static int do_mlockall(int flags)
{
struct vm_area_struct * vma, * prev = NULL;
unsigned int def_flags = 0;
if (flags & MCL_FUTURE)
def_flags = VM_LOCKED;
current->mm->def_flags = def_flags;
if (flags == MCL_FUTURE)
goto out;
for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
unsigned int newflags;
newflags = vma->vm_flags | VM_LOCKED;
if (!(flags & MCL_CURRENT))
newflags &= ~VM_LOCKED;
/* Ignore errors */
mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
}
out:
return 0;
}
SYSCALL_DEFINE1(mlockall, int, flags)
{
unsigned long lock_limit;
int ret = -EINVAL;
if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
goto out;
ret = -EPERM;
if (!can_do_mlock())
goto out;
lru_add_drain_all(); /* flush pagevec */
down_write(&current->mm->mmap_sem);
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
ret = -ENOMEM;
if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
capable(CAP_IPC_LOCK))
ret = do_mlockall(flags);
up_write(&current->mm->mmap_sem);
out:
return ret;
}
SYSCALL_DEFINE0(munlockall)
{
int ret;
down_write(&current->mm->mmap_sem);
ret = do_mlockall(0);
up_write(&current->mm->mmap_sem);
return ret;
}
/*
* Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
* shm segments) get accounted against the user_struct instead.
*/
static DEFINE_SPINLOCK(shmlock_user_lock);
int user_shm_lock(size_t size, struct user_struct *user)
{
unsigned long lock_limit, locked;
int allowed = 0;
locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
lock_limit = rlimit(RLIMIT_MEMLOCK);
if (lock_limit == RLIM_INFINITY)
allowed = 1;
lock_limit >>= PAGE_SHIFT;
spin_lock(&shmlock_user_lock);
if (!allowed &&
locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
goto out;
get_uid(user);
user->locked_shm += locked;
allowed = 1;
out:
spin_unlock(&shmlock_user_lock);
return allowed;
}
void user_shm_unlock(size_t size, struct user_struct *user)
{
spin_lock(&shmlock_user_lock);
user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
spin_unlock(&shmlock_user_lock);
free_uid(user);
}