mm: protect VMA modifications using VMA sequence count
The VMA sequence count has been introduced to allow fast detection of
VMA modification when running a page fault handler without holding
the mmap_sem.
This patch provides protection against the VMA modification done in :
- madvise()
- mpol_rebind_policy()
- vma_replace_policy()
- change_prot_numa()
- mlock(), munlock()
- mprotect()
- mmap_region()
- collapse_huge_page()
- userfaultd registering services
In addition, VMA fields which will be read during the speculative fault
path needs to be written using WRITE_ONCE to prevent write to be split
and intermediate values to be pushed to other CPUs.
Change-Id: Ic36046b7254e538b6baf7144c50ae577ee7f2074
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Patch-mainline: linux-mm @ Tue, 17 Apr 2018 16:33:15
[vinmenon@codeaurora.org: trivial merge conflict fixes]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
[charante@codeaurora.org: trivial merge conflict fixes]
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 9beff19..ab5568f 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -664,8 +664,11 @@
octx = vma->vm_userfaultfd_ctx.ctx;
if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
+ vm_write_begin(vma);
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
- vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
+ WRITE_ONCE(vma->vm_flags,
+ vma->vm_flags & ~(VM_UFFD_WP | VM_UFFD_MISSING));
+ vm_write_end(vma);
return 0;
}
@@ -904,8 +907,10 @@
vma = prev;
else
prev = vma;
- vma->vm_flags = new_flags;
+ vm_write_begin(vma);
+ WRITE_ONCE(vma->vm_flags, new_flags);
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
+ vm_write_end(vma);
}
up_write(&mm->mmap_sem);
mmput(mm);
@@ -1468,8 +1473,10 @@
* the next vma was merged into the current one and
* the current one has not been updated yet.
*/
- vma->vm_flags = new_flags;
+ vm_write_begin(vma);
+ WRITE_ONCE(vma->vm_flags, new_flags);
vma->vm_userfaultfd_ctx.ctx = ctx;
+ vm_write_end(vma);
skip:
prev = vma;
@@ -1629,8 +1636,10 @@
* the next vma was merged into the current one and
* the current one has not been updated yet.
*/
- vma->vm_flags = new_flags;
+ vm_write_begin(vma);
+ WRITE_ONCE(vma->vm_flags, new_flags);
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
+ vm_write_end(vma);
skip:
prev = vma;