Commit 538f8ea6 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds

mm: xip fix fault vs sparse page invalidate race

XIP has a race between sparse pages being inserted into page tables, and
sparse pages being zapped when its time to put a non-sparse page in.

What can happen is that a process can be left with a dangling sparse page
in a MAP_SHARED mapping, while the rest of the world sees the non-sparse
version.  Ie.  data corruption.

Guard these operations with a seqlock, making fault-in-sparse-pages the
slowpath, and try-to-unmap-sparse-pages the fastpath.
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Jared Hulbert <jaredeh@gmail.com>
Acked-by: default avatarCarsten Otte <cotte@freenet.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 479db0bf
......@@ -15,6 +15,8 @@
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/sched.h>
#include <linux/seqlock.h>
#include <linux/mutex.h>
#include <asm/tlbflush.h>
#include <asm/io.h>
......@@ -22,22 +24,18 @@
* We do use our own empty page to avoid interference with other users
* of ZERO_PAGE(), such as /dev/zero
*/
static DEFINE_MUTEX(xip_sparse_mutex);
static seqcount_t xip_sparse_seq = SEQCNT_ZERO;
static struct page *__xip_sparse_page;
/* called under xip_sparse_mutex */
static struct page *xip_sparse_page(void)
{
if (!__xip_sparse_page) {
struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
if (page) {
static DEFINE_SPINLOCK(xip_alloc_lock);
spin_lock(&xip_alloc_lock);
if (!__xip_sparse_page)
__xip_sparse_page = page;
else
__free_page(page);
spin_unlock(&xip_alloc_lock);
}
if (page)
__xip_sparse_page = page;
}
return __xip_sparse_page;
}
......@@ -174,11 +172,16 @@ __xip_unmap (struct address_space * mapping,
pte_t pteval;
spinlock_t *ptl;
struct page *page;
unsigned count;
int locked = 0;
count = read_seqcount_begin(&xip_sparse_seq);
page = __xip_sparse_page;
if (!page)
return;
retry:
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
mm = vma->vm_mm;
......@@ -198,6 +201,14 @@ __xip_unmap (struct address_space * mapping,
}
}
spin_unlock(&mapping->i_mmap_lock);
if (locked) {
mutex_unlock(&xip_sparse_mutex);
} else if (read_seqcount_retry(&xip_sparse_seq, count)) {
mutex_lock(&xip_sparse_mutex);
locked = 1;
goto retry;
}
}
/*
......@@ -218,7 +229,7 @@ static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
int error;
/* XXX: are VM_FAULT_ codes OK? */
again:
size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (vmf->pgoff >= size)
return VM_FAULT_SIGBUS;
......@@ -245,6 +256,7 @@ static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
__xip_unmap(mapping, vmf->pgoff);
found:
printk("%s insert %lx@%lx\n", current->comm, (unsigned long)vmf->virtual_address, xip_pfn);
err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
xip_pfn);
if (err == -ENOMEM)
......@@ -252,14 +264,34 @@ static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
BUG_ON(err);
return VM_FAULT_NOPAGE;
} else {
int err, ret = VM_FAULT_OOM;
mutex_lock(&xip_sparse_mutex);
write_seqcount_begin(&xip_sparse_seq);
error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
&xip_mem, &xip_pfn);
if (unlikely(!error)) {
write_seqcount_end(&xip_sparse_seq);
mutex_unlock(&xip_sparse_mutex);
goto again;
}
if (error != -ENODATA)
goto out;
/* not shared and writable, use xip_sparse_page() */
page = xip_sparse_page();
if (!page)
return VM_FAULT_OOM;
goto out;
err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
page);
if (err == -ENOMEM)
goto out;
page_cache_get(page);
vmf->page = page;
return 0;
ret = VM_FAULT_NOPAGE;
out:
write_seqcount_end(&xip_sparse_seq);
mutex_unlock(&xip_sparse_mutex);
return ret;
}
}
......
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