On Tue, Sep 6, 2022 at 7:27 AM Laurent Dufour [off-list ref] wrote:

Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :

quoted

VMA flag modifications should be done under VMA lock to prevent concurrent
page fault handling in that area.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 fs/proc/task_mmu.c | 1 +
 fs/userfaultfd.c   | 6 ++++++
 mm/madvise.c       | 1 +
 mm/mlock.c         | 2 ++
 mm/mmap.c          | 1 +
 mm/mprotect.c      | 1 +
 6 files changed, 12 insertions(+)

There are few changes also done in the driver's space, for instance:

*** arch/x86/kernel/cpu/sgx/driver.c:
sgx_mmap[98]                   vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND |
VM_DONTDUMP | VM_IO;
*** arch/x86/kernel/cpu/sgx/virt.c:
sgx_vepc_mmap[108]             vma->vm_flags |= VM_PFNMAP | VM_IO |
VM_DONTDUMP | VM_DONTCOPY;
*** drivers/dax/device.c:
dax_mmap[311]                  vma->vm_flags |= VM_HUGEPAGE;

I guess these changes to vm_flags should be protected as well, or to be
checked one by one.

Thanks for noting these! I'll add necessary locking here and will look
for other places I might have missed.

quoted

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 4e0023643f8b..ceffa5c2c650 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c

@@ -1285,6 +1285,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
                      for (vma = mm->mmap; vma; vma = vma->vm_next) {
                              if (!(vma->vm_flags & VM_SOFTDIRTY))
                                      continue;
+                             vma_mark_locked(vma);
                              vma->vm_flags &= ~VM_SOFTDIRTY;
                              vma_set_page_prot(vma);
                      }

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 175de70e3adf..fe557b3d1c07 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c

@@ -620,6 +620,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
              mmap_write_lock(mm);
              for (vma = mm->mmap; vma; vma = vma->vm_next)
                      if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
+                             vma_mark_locked(vma);
                              vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
                              vma->vm_flags &= ~__VM_UFFD_FLAGS;
                      }

@@ -653,6 +654,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)

      octx = vma->vm_userfaultfd_ctx.ctx;
      if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
+             vma_mark_locked(vma);
              vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
              vma->vm_flags &= ~__VM_UFFD_FLAGS;
              return 0;

@@ -734,6 +736,7 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
              atomic_inc(&ctx->mmap_changing);
      } else {
              /* Drop uffd context if remap feature not enabled */
+             vma_mark_locked(vma);
              vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
              vma->vm_flags &= ~__VM_UFFD_FLAGS;
      }

@@ -891,6 +894,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
                      vma = prev;
              else
                      prev = vma;
+             vma_mark_locked(vma);
              vma->vm_flags = new_flags;
              vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
      }

@@ -1449,6 +1453,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
               * the next vma was merged into the current one and
               * the current one has not been updated yet.
               */
+             vma_mark_locked(vma);
              vma->vm_flags = new_flags;
              vma->vm_userfaultfd_ctx.ctx = ctx;

@@ -1630,6 +1635,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
               * the next vma was merged into the current one and
               * the current one has not been updated yet.
               */
+             vma_mark_locked(vma);
              vma->vm_flags = new_flags;
              vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;

diff --git a/mm/madvise.c b/mm/madvise.c
index 5f0f0948a50e..a173f0025abd 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c

@@ -181,6 +181,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
      /*
       * vm_flags is protected by the mmap_lock held in write mode.
       */
+     vma_mark_locked(vma);
      vma->vm_flags = new_flags;
      if (!vma->vm_file) {
              error = replace_anon_vma_name(vma, anon_name);

diff --git a/mm/mlock.c b/mm/mlock.c
index b14e929084cc..f62e1a4d05f2 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c

@@ -380,6 +380,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
       */
      if (newflags & VM_LOCKED)
              newflags |= VM_IO;
+     vma_mark_locked(vma);
      WRITE_ONCE(vma->vm_flags, newflags);

      lru_add_drain();

@@ -456,6 +457,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,

      if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) {
              /* No work to do, and mlocking twice would be wrong */
+             vma_mark_locked(vma);
              vma->vm_flags = newflags;
      } else {
              mlock_vma_pages_range(vma, start, end, newflags);

diff --git a/mm/mmap.c b/mm/mmap.c
index 693e6776be39..f89c9b058105 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -1818,6 +1818,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 out:
      perf_event_mmap(vma);

+     vma_mark_locked(vma);
      vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
      if (vm_flags & VM_LOCKED) {
              if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||

I guess, this doesn't really impact, but the call to vma_mark_locked(vma)
may be done only in the case the vm_flags field is touched.
Something like this:

        vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
                                        is_vm_hugetlb_page(vma) ||
-                                       vma == get_gate_vma(current->mm))
+                                       vma == get_gate_vma(current->mm)) {
+                       vma_mark_locked(vma);
                        vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
-               else
+               } else
                        mm->locked_vm += (len >> PAGE_SHIFT);
        }

quoted

diff --git a/mm/mprotect.c b/mm/mprotect.c
index bc6bddd156ca..df47fc21b0e4 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c

@@ -621,6 +621,7 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,
       * vm_flags and vm_page_prot are protected by the mmap_lock
       * held in write mode.
       */
+     vma_mark_locked(vma);
      vma->vm_flags = newflags;
      /*
       * We want to check manually if we can change individual PTEs writable