linux/mm/mprotect.c
Rik van Riel 2084140594 mm: fix TLB flush race between migration, and change_protection_range
There are a few subtle races, between change_protection_range (used by
mprotect and change_prot_numa) on one side, and NUMA page migration and
compaction on the other side.

The basic race is that there is a time window between when the PTE gets
made non-present (PROT_NONE or NUMA), and the TLB is flushed.

During that time, a CPU may continue writing to the page.

This is fine most of the time, however compaction or the NUMA migration
code may come in, and migrate the page away.

When that happens, the CPU may continue writing, through the cached
translation, to what is no longer the current memory location of the
process.

This only affects x86, which has a somewhat optimistic pte_accessible.
All other architectures appear to be safe, and will either always flush,
or flush whenever there is a valid mapping, even with no permissions
(SPARC).

The basic race looks like this:

CPU A			CPU B			CPU C

						load TLB entry
make entry PTE/PMD_NUMA
			fault on entry
						read/write old page
			start migrating page
			change PTE/PMD to new page
						read/write old page [*]
flush TLB
						reload TLB from new entry
						read/write new page
						lose data

[*] the old page may belong to a new user at this point!

The obvious fix is to flush remote TLB entries, by making sure that
pte_accessible aware of the fact that PROT_NONE and PROT_NUMA memory may
still be accessible if there is a TLB flush pending for the mm.

This should fix both NUMA migration and compaction.

[mgorman@suse.de: fix build]
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-12-18 19:04:51 -08:00

409 lines
9.7 KiB
C

/*
* mm/mprotect.c
*
* (C) Copyright 1994 Linus Torvalds
* (C) Copyright 2002 Christoph Hellwig
*
* Address space accounting code <alan@lxorguk.ukuu.org.uk>
* (C) Copyright 2002 Red Hat Inc, All Rights Reserved
*/
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/mempolicy.h>
#include <linux/personality.h>
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/perf_event.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
#ifndef pgprot_modify
static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
{
return newprot;
}
#endif
static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
pte_t *pte, oldpte;
spinlock_t *ptl;
unsigned long pages = 0;
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
arch_enter_lazy_mmu_mode();
do {
oldpte = *pte;
if (pte_present(oldpte)) {
pte_t ptent;
bool updated = false;
if (!prot_numa) {
ptent = ptep_modify_prot_start(mm, addr, pte);
if (pte_numa(ptent))
ptent = pte_mknonnuma(ptent);
ptent = pte_modify(ptent, newprot);
updated = true;
} else {
struct page *page;
ptent = *pte;
page = vm_normal_page(vma, addr, oldpte);
if (page) {
if (!pte_numa(oldpte)) {
ptent = pte_mknuma(ptent);
set_pte_at(mm, addr, pte, ptent);
updated = true;
}
}
}
/*
* Avoid taking write faults for pages we know to be
* dirty.
*/
if (dirty_accountable && pte_dirty(ptent)) {
ptent = pte_mkwrite(ptent);
updated = true;
}
if (updated)
pages++;
/* Only !prot_numa always clears the pte */
if (!prot_numa)
ptep_modify_prot_commit(mm, addr, pte, ptent);
} else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
swp_entry_t entry = pte_to_swp_entry(oldpte);
if (is_write_migration_entry(entry)) {
pte_t newpte;
/*
* A protection check is difficult so
* just be safe and disable write
*/
make_migration_entry_read(&entry);
newpte = swp_entry_to_pte(entry);
if (pte_swp_soft_dirty(oldpte))
newpte = pte_swp_mksoft_dirty(newpte);
set_pte_at(mm, addr, pte, newpte);
pages++;
}
}
} while (pte++, addr += PAGE_SIZE, addr != end);
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(pte - 1, ptl);
return pages;
}
static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
pud_t *pud, unsigned long addr, unsigned long end,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
pmd_t *pmd;
unsigned long next;
unsigned long pages = 0;
unsigned long nr_huge_updates = 0;
pmd = pmd_offset(pud, addr);
do {
unsigned long this_pages;
next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE)
split_huge_page_pmd(vma, addr, pmd);
else {
int nr_ptes = change_huge_pmd(vma, pmd, addr,
newprot, prot_numa);
if (nr_ptes) {
if (nr_ptes == HPAGE_PMD_NR) {
pages += HPAGE_PMD_NR;
nr_huge_updates++;
}
continue;
}
}
/* fall through */
}
if (pmd_none_or_clear_bad(pmd))
continue;
this_pages = change_pte_range(vma, pmd, addr, next, newprot,
dirty_accountable, prot_numa);
pages += this_pages;
} while (pmd++, addr = next, addr != end);
if (nr_huge_updates)
count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
return pages;
}
static inline unsigned long change_pud_range(struct vm_area_struct *vma,
pgd_t *pgd, unsigned long addr, unsigned long end,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
pud_t *pud;
unsigned long next;
unsigned long pages = 0;
pud = pud_offset(pgd, addr);
do {
next = pud_addr_end(addr, end);
if (pud_none_or_clear_bad(pud))
continue;
pages += change_pmd_range(vma, pud, addr, next, newprot,
dirty_accountable, prot_numa);
} while (pud++, addr = next, addr != end);
return pages;
}
static unsigned long change_protection_range(struct vm_area_struct *vma,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
unsigned long next;
unsigned long start = addr;
unsigned long pages = 0;
BUG_ON(addr >= end);
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
set_tlb_flush_pending(mm);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
continue;
pages += change_pud_range(vma, pgd, addr, next, newprot,
dirty_accountable, prot_numa);
} while (pgd++, addr = next, addr != end);
/* Only flush the TLB if we actually modified any entries: */
if (pages)
flush_tlb_range(vma, start, end);
clear_tlb_flush_pending(mm);
return pages;
}
unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long pages;
mmu_notifier_invalidate_range_start(mm, start, end);
if (is_vm_hugetlb_page(vma))
pages = hugetlb_change_protection(vma, start, end, newprot);
else
pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
mmu_notifier_invalidate_range_end(mm, start, end);
return pages;
}
int
mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
unsigned long start, unsigned long end, unsigned long newflags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long oldflags = vma->vm_flags;
long nrpages = (end - start) >> PAGE_SHIFT;
unsigned long charged = 0;
pgoff_t pgoff;
int error;
int dirty_accountable = 0;
if (newflags == oldflags) {
*pprev = vma;
return 0;
}
/*
* If we make a private mapping writable we increase our commit;
* but (without finer accounting) cannot reduce our commit if we
* make it unwritable again. hugetlb mapping were accounted for
* even if read-only so there is no need to account for them here
*/
if (newflags & VM_WRITE) {
if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
VM_SHARED|VM_NORESERVE))) {
charged = nrpages;
if (security_vm_enough_memory_mm(mm, charged))
return -ENOMEM;
newflags |= VM_ACCOUNT;
}
}
/*
* First try to merge with previous and/or next vma.
*/
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*pprev = vma_merge(mm, *pprev, start, end, newflags,
vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
if (*pprev) {
vma = *pprev;
goto success;
}
*pprev = vma;
if (start != vma->vm_start) {
error = split_vma(mm, vma, start, 1);
if (error)
goto fail;
}
if (end != vma->vm_end) {
error = split_vma(mm, vma, end, 0);
if (error)
goto fail;
}
success:
/*
* vm_flags and vm_page_prot are protected by the mmap_sem
* held in write mode.
*/
vma->vm_flags = newflags;
vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
vm_get_page_prot(newflags));
if (vma_wants_writenotify(vma)) {
vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
dirty_accountable = 1;
}
change_protection(vma, start, end, vma->vm_page_prot,
dirty_accountable, 0);
vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
vm_stat_account(mm, newflags, vma->vm_file, nrpages);
perf_event_mmap(vma);
return 0;
fail:
vm_unacct_memory(charged);
return error;
}
SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
unsigned long, prot)
{
unsigned long vm_flags, nstart, end, tmp, reqprot;
struct vm_area_struct *vma, *prev;
int error = -EINVAL;
const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
return -EINVAL;
if (start & ~PAGE_MASK)
return -EINVAL;
if (!len)
return 0;
len = PAGE_ALIGN(len);
end = start + len;
if (end <= start)
return -ENOMEM;
if (!arch_validate_prot(prot))
return -EINVAL;
reqprot = prot;
/*
* Does the application expect PROT_READ to imply PROT_EXEC:
*/
if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
prot |= PROT_EXEC;
vm_flags = calc_vm_prot_bits(prot);
down_write(&current->mm->mmap_sem);
vma = find_vma(current->mm, start);
error = -ENOMEM;
if (!vma)
goto out;
prev = vma->vm_prev;
if (unlikely(grows & PROT_GROWSDOWN)) {
if (vma->vm_start >= end)
goto out;
start = vma->vm_start;
error = -EINVAL;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto out;
} else {
if (vma->vm_start > start)
goto out;
if (unlikely(grows & PROT_GROWSUP)) {
end = vma->vm_end;
error = -EINVAL;
if (!(vma->vm_flags & VM_GROWSUP))
goto out;
}
}
if (start > vma->vm_start)
prev = vma;
for (nstart = start ; ; ) {
unsigned long newflags;
/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
newflags = vm_flags;
newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
/* newflags >> 4 shift VM_MAY% in place of VM_% */
if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
error = -EACCES;
goto out;
}
error = security_file_mprotect(vma, reqprot, prot);
if (error)
goto out;
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
if (error)
goto out;
nstart = tmp;
if (nstart < prev->vm_end)
nstart = prev->vm_end;
if (nstart >= end)
goto out;
vma = prev->vm_next;
if (!vma || vma->vm_start != nstart) {
error = -ENOMEM;
goto out;
}
}
out:
up_write(&current->mm->mmap_sem);
return error;
}