[PATCH 5.4.y 0/3] Backport series: "permit write-sealed memfd read-only shared mappings"

[PATCH 5.4.y 0/3] Backport series: "permit write-sealed memfd read-only shared mappings"

[Isaac J. Manjarres]

Hello,

Until kernel version 6.7, a write-sealed memfd could not be mapped as
shared and read-only. This was clearly a bug, and was not inline with
the description of F_SEAL_WRITE in the man page for fcntl()[1].

Lorenzo's series [2] fixed that issue and was merged in kernel version
6.7, but was not backported to older kernels. So, this issue is still
present on kernels 5.4, 5.10, 5.15, 6.1, and 6.6.

This series backports Lorenzo's series to the 5.4 kernel.

[1] https://man7.org/linux/man-pages/man2/fcntl.2.html
[2] https://lore.kernel.org/all/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com/T/#m28fbfb0d5727e5693e54a7fb2e0c9ac30e95eca5

Lorenzo Stoakes (3):
  mm: drop the assumption that VM_SHARED always implies writable
  mm: update memfd seal write check to include F_SEAL_WRITE
  mm: perform the mapping_map_writable() check after call_mmap()

 fs/hugetlbfs/inode.c |  2 +-
 include/linux/fs.h   |  4 ++--
 include/linux/mm.h   | 26 +++++++++++++++++++-------
 kernel/fork.c        |  2 +-
 mm/filemap.c         |  2 +-
 mm/madvise.c         |  2 +-
 mm/mmap.c            | 26 ++++++++++++++++----------
 mm/shmem.c           |  2 +-
 8 files changed, 42 insertions(+), 24 deletions(-)

-- 
2.50.1.552.g942d659e1b-goog

[PATCH 5.4.y 1/3] mm: drop the assumption that VM_SHARED always implies writable

[Isaac J. Manjarres]

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit e8e17ee90eaf650c855adb0a3e5e965fd6692ff1 ]

Patch series "permit write-sealed memfd read-only shared mappings", v4.

The man page for fcntl() describing memfd file seals states the following
about F_SEAL_WRITE:-

    Furthermore, trying to create new shared, writable memory-mappings via
    mmap(2) will also fail with EPERM.

With emphasis on 'writable'.  In turns out in fact that currently the
kernel simply disallows all new shared memory mappings for a memfd with
F_SEAL_WRITE applied, rendering this documentation inaccurate.

This matters because users are therefore unable to obtain a shared mapping
to a memfd after write sealing altogether, which limits their usefulness.
This was reported in the discussion thread [1] originating from a bug
report [2].

This is a product of both using the struct address_space->i_mmap_writable
atomic counter to determine whether writing may be permitted, and the
kernel adjusting this counter when any VM_SHARED mapping is performed and
more generally implicitly assuming VM_SHARED implies writable.

It seems sensible that we should only update this mapping if VM_MAYWRITE
is specified, i.e.  whether it is possible that this mapping could at any
point be written to.

If we do so then all we need to do to permit write seals to function as
documented is to clear VM_MAYWRITE when mapping read-only.  It turns out
this functionality already exists for F_SEAL_FUTURE_WRITE - we can
therefore simply adapt this logic to do the same for F_SEAL_WRITE.

We then hit a chicken and egg situation in mmap_region() where the check
for VM_MAYWRITE occurs before we are able to clear this flag.  To work
around this, perform this check after we invoke call_mmap(), with careful
consideration of error paths.

Thanks to Andy Lutomirski for the suggestion!

[1]:https://lore.kernel.org/all/20230324133646.16101dfa666f253c4715d965@linux-foundation.org/
[2]:https://bugzilla.kernel.org/show_bug.cgi?id=217238

This patch (of 3):

There is a general assumption that VMAs with the VM_SHARED flag set are
writable.  If the VM_MAYWRITE flag is not set, then this is simply not the
case.

Update those checks which affect the struct address_space->i_mmap_writable
field to explicitly test for this by introducing
[vma_]is_shared_maywrite() helper functions.

This remains entirely conservative, as the lack of VM_MAYWRITE guarantees
that the VMA cannot be written to.

Link: https://lkml.kernel.org/r/cover.1697116581.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/d978aefefa83ec42d18dfa964ad180dbcde34795.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
---
 include/linux/fs.h |  4 ++--
 include/linux/mm.h | 11 +++++++++++
 kernel/fork.c      |  2 +-
 mm/filemap.c       |  2 +-
 mm/madvise.c       |  2 +-
 mm/mmap.c          | 10 +++++-----
 6 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index d3648a55590c..c5985d72d60e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -430,7 +430,7 @@ int pagecache_write_end(struct file *, struct address_space *mapping,
  * @host: Owner, either the inode or the block_device.
  * @i_pages: Cached pages.
  * @gfp_mask: Memory allocation flags to use for allocating pages.
- * @i_mmap_writable: Number of VM_SHARED mappings.
+ * @i_mmap_writable: Number of VM_SHARED, VM_MAYWRITE mappings.
  * @nr_thps: Number of THPs in the pagecache (non-shmem only).
  * @i_mmap: Tree of private and shared mappings.
  * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable.
@@ -553,7 +553,7 @@ static inline int mapping_mapped(struct address_space *mapping)
 
 /*
  * Might pages of this file have been modified in userspace?
- * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap_pgoff
+ * Note that i_mmap_writable counts all VM_SHARED, VM_MAYWRITE vmas: do_mmap_pgoff
  * marks vma as VM_SHARED if it is shared, and the file was opened for
  * writing i.e. vma may be mprotected writable even if now readonly.
  *
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4d3657b630db..47d56c96447a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -549,6 +549,17 @@ static inline bool vma_is_anonymous(struct vm_area_struct *vma)
 	return !vma->vm_ops;
 }
 
+static inline bool is_shared_maywrite(vm_flags_t vm_flags)
+{
+	return (vm_flags & (VM_SHARED | VM_MAYWRITE)) ==
+		(VM_SHARED | VM_MAYWRITE);
+}
+
+static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma)
+{
+	return is_shared_maywrite(vma->vm_flags);
+}
+
 #ifdef CONFIG_SHMEM
 /*
  * The vma_is_shmem is not inline because it is used only by slow
diff --git a/kernel/fork.c b/kernel/fork.c
index e71f96bff1dc..ad3e6e91d828 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -566,7 +566,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 			if (tmp->vm_flags & VM_DENYWRITE)
 				atomic_dec(&inode->i_writecount);
 			i_mmap_lock_write(mapping);
-			if (tmp->vm_flags & VM_SHARED)
+			if (vma_is_shared_maywrite(tmp))
 				atomic_inc(&mapping->i_mmap_writable);
 			flush_dcache_mmap_lock(mapping);
 			/* insert tmp into the share list, just after mpnt */
diff --git a/mm/filemap.c b/mm/filemap.c
index f1ed0400c37c..af3efb23262b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2876,7 +2876,7 @@ int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
  */
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+	if (vma_is_shared_maywrite(vma))
 		return -EINVAL;
 	return generic_file_mmap(file, vma);
 }
diff --git a/mm/madvise.c b/mm/madvise.c
index ac8d68c488b5..3f5331c96ad5 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -839,7 +839,7 @@ static long madvise_remove(struct vm_area_struct *vma,
 			return -EINVAL;
 	}
 
-	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
+	if (!vma_is_shared_maywrite(vma))
 		return -EACCES;
 
 	offset = (loff_t)(start - vma->vm_start)
diff --git a/mm/mmap.c b/mm/mmap.c
index eeebbb20accf..cb712ae731cd 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -141,7 +141,7 @@ static void __remove_shared_vm_struct(struct vm_area_struct *vma,
 {
 	if (vma->vm_flags & VM_DENYWRITE)
 		atomic_inc(&file_inode(file)->i_writecount);
-	if (vma->vm_flags & VM_SHARED)
+	if (vma_is_shared_maywrite(vma))
 		mapping_unmap_writable(mapping);
 
 	flush_dcache_mmap_lock(mapping);
@@ -619,7 +619,7 @@ static void __vma_link_file(struct vm_area_struct *vma)
 
 		if (vma->vm_flags & VM_DENYWRITE)
 			atomic_dec(&file_inode(file)->i_writecount);
-		if (vma->vm_flags & VM_SHARED)
+		if (vma_is_shared_maywrite(vma))
 			atomic_inc(&mapping->i_mmap_writable);
 
 		flush_dcache_mmap_lock(mapping);
@@ -1785,7 +1785,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			if (error)
 				goto free_vma;
 		}
-		if (vm_flags & VM_SHARED) {
+		if (is_shared_maywrite(vm_flags)) {
 			error = mapping_map_writable(file->f_mapping);
 			if (error)
 				goto allow_write_and_free_vma;
@@ -1823,7 +1823,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	/* Once vma denies write, undo our temporary denial count */
 	if (file) {
-		if (vm_flags & VM_SHARED)
+		if (is_shared_maywrite(vm_flags))
 			mapping_unmap_writable(file->f_mapping);
 		if (vm_flags & VM_DENYWRITE)
 			allow_write_access(file);
@@ -1864,7 +1864,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
-	if (vm_flags & VM_SHARED)
+	if (is_shared_maywrite(vm_flags))
 		mapping_unmap_writable(file->f_mapping);
 allow_write_and_free_vma:
 	if (vm_flags & VM_DENYWRITE)
-- 
2.50.1.552.g942d659e1b-goog

[PATCH 5.4.y 2/3] mm: update memfd seal write check to include F_SEAL_WRITE

[Isaac J. Manjarres]

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 28464bbb2ddc199433383994bcb9600c8034afa1 ]

The seal_check_future_write() function is called by shmem_mmap() or
hugetlbfs_file_mmap() to disallow any future writable mappings of an memfd
sealed this way.

The F_SEAL_WRITE flag is not checked here, as that is handled via the
mapping->i_mmap_writable mechanism and so any attempt at a mapping would
fail before this could be run.

However we intend to change this, meaning this check can be performed for
F_SEAL_WRITE mappings also.

The logic here is equally applicable to both flags, so update this
function to accommodate both and rename it accordingly.

Link: https://lkml.kernel.org/r/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
---
 fs/hugetlbfs/inode.c |  2 +-
 include/linux/mm.h   | 15 ++++++++-------
 mm/shmem.c           |  2 +-
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 47b292f9b4f8..c18a47a86e8b 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -152,7 +152,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 	vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
 	vma->vm_ops = &hugetlb_vm_ops;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 47d56c96447a..57cba6e4fdcd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2946,25 +2946,26 @@ static inline int pages_identical(struct page *page1, struct page *page2)
 }
 
 /**
- * seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it
+ * seal_check_write - Check for F_SEAL_WRITE or F_SEAL_FUTURE_WRITE flags and
+ *                    handle them.
  * @seals: the seals to check
  * @vma: the vma to operate on
  *
- * Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on
- * the vma flags.  Return 0 if check pass, or <0 for errors.
+ * Check whether F_SEAL_WRITE or F_SEAL_FUTURE_WRITE are set; if so, do proper
+ * check/handling on the vma flags.  Return 0 if check pass, or <0 for errors.
  */
-static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
+static inline int seal_check_write(int seals, struct vm_area_struct *vma)
 {
-	if (seals & F_SEAL_FUTURE_WRITE) {
+	if (seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
 		/*
 		 * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
-		 * "future write" seal active.
+		 * write seals are active.
 		 */
 		if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
 			return -EPERM;
 
 		/*
-		 * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as
+		 * Since an F_SEAL_[FUTURE_]WRITE sealed memfd can be mapped as
 		 * MAP_SHARED and read-only, take care to not allow mprotect to
 		 * revert protections on such mappings. Do this only for shared
 		 * mappings. For private mappings, don't need to mask
diff --git a/mm/shmem.c b/mm/shmem.c
index 264229680ad7..8475d56f5977 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2215,7 +2215,7 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 	struct shmem_inode_info *info = SHMEM_I(file_inode(file));
 	int ret;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 
-- 
2.50.1.552.g942d659e1b-goog

[PATCH 5.4.y 3/3] mm: perform the mapping_map_writable() check after call_mmap()

[Isaac J. Manjarres]

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 158978945f3173b8c1a88f8c5684a629736a57ac ]

In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to
clear VM_MAYWRITE, we must be able to invoke the appropriate
vm_ops->mmap() handler to do so.  We would otherwise fail the
mapping_map_writable() check before we had the opportunity to avoid it.

This patch moves this check after the call_mmap() invocation.  Only memfd
actively denies write access causing a potential failure here (in
memfd_add_seals()), so there should be no impact on non-memfd cases.

This patch makes the userland-visible change that MAP_SHARED, PROT_READ
mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed.

There is a delicate situation with cleanup paths assuming that a writable
mapping must have occurred in circumstances where it may now not have.  In
order to ensure we do not accidentally mark a writable file unwritable by
mistake, we explicitly track whether we have a writable mapping and unmap
only if we do.

[lstoakes@gmail.com: do not set writable_file_mapping in inappropriate case]
  Link: https://lkml.kernel.org/r/c9eb4cc6-7db4-4c2b-838d-43a0b319a4f0@lucifer.local
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238
Link: https://lkml.kernel.org/r/55e413d20678a1bb4c7cce889062bbb07b0df892.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
[isaacmanjarres: added error handling to cleanup the work done by the
mmap() callback and removed unused label.]
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
---
 mm/mmap.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index cb712ae731cd..e591a82a26a8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1718,6 +1718,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
+	bool writable_file_mapping = false;
 	int error;
 	struct rb_node **rb_link, *rb_parent;
 	unsigned long charged = 0;
@@ -1785,11 +1786,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			if (error)
 				goto free_vma;
 		}
-		if (is_shared_maywrite(vm_flags)) {
-			error = mapping_map_writable(file->f_mapping);
-			if (error)
-				goto allow_write_and_free_vma;
-		}
 
 		/* ->mmap() can change vma->vm_file, but must guarantee that
 		 * vma_link() below can deny write-access if VM_DENYWRITE is set
@@ -1801,6 +1797,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 		if (error)
 			goto unmap_and_free_vma;
 
+		if (vma_is_shared_maywrite(vma)) {
+			error = mapping_map_writable(file->f_mapping);
+			if (error)
+				goto close_and_free_vma;
+
+			writable_file_mapping = true;
+		}
+
 		/* Can addr have changed??
 		 *
 		 * Answer: Yes, several device drivers can do it in their
@@ -1823,7 +1827,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	/* Once vma denies write, undo our temporary denial count */
 	if (file) {
-		if (is_shared_maywrite(vm_flags))
+		if (writable_file_mapping)
 			mapping_unmap_writable(file->f_mapping);
 		if (vm_flags & VM_DENYWRITE)
 			allow_write_access(file);
@@ -1858,15 +1862,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	return addr;
 
+close_and_free_vma:
+	if (vma->vm_ops && vma->vm_ops->close)
+		vma->vm_ops->close(vma);
 unmap_and_free_vma:
 	vma->vm_file = NULL;
 	fput(file);
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
-	if (is_shared_maywrite(vm_flags))
+	if (writable_file_mapping)
 		mapping_unmap_writable(file->f_mapping);
-allow_write_and_free_vma:
 	if (vm_flags & VM_DENYWRITE)
 		allow_write_access(file);
 free_vma:
-- 
2.50.1.552.g942d659e1b-goog

Re: [PATCH 5.4.y 0/3] Backport series: "permit write-sealed memfd read-only shared mappings"

[Matthew Wilcox]

On Tue, Jul 29, 2025 at 05:58:05PM -0700, Isaac J. Manjarres wrote:
> Lorenzo's series [2] fixed that issue and was merged in kernel version
> 6.7, but was not backported to older kernels. So, this issue is still
> present on kernels 5.4, 5.10, 5.15, 6.1, and 6.6.
> 
> This series backports Lorenzo's series to the 5.4 kernel.

That's not how this works.  First you do 6.6, then 6.1, then 5.15 ...

Otherwise somebody might upgrade from 5.4 to 6.1 and see a regression.

Re: [PATCH 5.4.y 0/3] Backport series: "permit write-sealed memfd read-only shared mappings"

[Isaac Manjarres]

On Wed, Jul 30, 2025 at 02:27:29AM +0100, Matthew Wilcox wrote:
> On Tue, Jul 29, 2025 at 05:58:05PM -0700, Isaac J. Manjarres wrote:
> > Lorenzo's series [2] fixed that issue and was merged in kernel version
> > 6.7, but was not backported to older kernels. So, this issue is still
> > present on kernels 5.4, 5.10, 5.15, 6.1, and 6.6.
> > 
> > This series backports Lorenzo's series to the 5.4 kernel.
> 
> That's not how this works.  First you do 6.6, then 6.1, then 5.15 ...

Hey Matthew,

Thanks for pointing that out. I'm sorry about the confusion. I did
prepare backports for the other kernel versions too, and the intent
was to send them together. However, my machine only sent the 5.4
version of the patches and not the rest.

I sent the patches for each kernel version and here are the relevant
links:

6.6: https://lore.kernel.org/all/20250730015152.29758-1-isaacmanjarres@google.com/
6.1: https://lore.kernel.org/all/20250730015247.30827-1-isaacmanjarres@google.com/
5.15: https://lore.kernel.org/all/20250730015337.31730-1-isaacmanjarres@google.com/
5.10: https://lore.kernel.org/all/20250730015406.32569-1-isaacmanjarres@google.com/

> Otherwise somebody might upgrade from 5.4 to 6.1 and see a regression.

Understood; sorry again for the confusion.

Thanks,
Isaac

Patch "mm: perform the mapping_map_writable() check after call_mmap()" has been added to the 5.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm: perform the mapping_map_writable() check after call_mmap()

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-perform-the-mapping_map_writable-check-after-call_mmap.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-165155-greg=kroah.com@vger.kernel.org Wed Jul 30 02:59:23 2025
From: "Isaac J. Manjarres" <isaacmanjarres@google.com>
Date: Tue, 29 Jul 2025 17:58:08 -0700
Subject: mm: perform the mapping_map_writable() check after call_mmap()
To: lorenzo.stoakes@oracle.com, gregkh@linuxfoundation.org,  Muchun Song <muchun.song@linux.dev>, Oscar Salvador <osalvador@suse.de>,  David Hildenbrand <david@redhat.com>, Alexander Viro <viro@zeniv.linux.org.uk>,  Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,  Andrew Morton <akpm@linux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@oracle.com>,  Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>, Suren Baghdasaryan <surenb@google.com>,  Michal Hocko <mhocko@suse.com>, Kees Cook <kees@kernel.org>, Ingo Molnar <mingo@redhat.com>,  Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>,  Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>,  Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,  Valentin Schneider <vschneid@redhat.com>, "Matthew Wilcox (Oracle)" <willy@infradead.org>, Jann Horn <jannh@google.com>,  Pedro Falcato <pfalcato@s
 use.de>,
  Hugh Dickins <hughd@google.com>,  Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: aliceryhl@google.com, stable@vger.kernel.org,  "Isaac J. Manjarres" <isaacmanjarres@google.com>, kernel-team@android.com, linux-mm@kvack.org,  linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,  Lorenzo Stoakes <lstoakes@gmail.com>, Andy Lutomirski <luto@kernel.org>,  Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <20250730005818.2793577-4-isaacmanjarres@google.com>

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 158978945f3173b8c1a88f8c5684a629736a57ac ]

In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to
clear VM_MAYWRITE, we must be able to invoke the appropriate
vm_ops->mmap() handler to do so.  We would otherwise fail the
mapping_map_writable() check before we had the opportunity to avoid it.

This patch moves this check after the call_mmap() invocation.  Only memfd
actively denies write access causing a potential failure here (in
memfd_add_seals()), so there should be no impact on non-memfd cases.

This patch makes the userland-visible change that MAP_SHARED, PROT_READ
mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed.

There is a delicate situation with cleanup paths assuming that a writable
mapping must have occurred in circumstances where it may now not have.  In
order to ensure we do not accidentally mark a writable file unwritable by
mistake, we explicitly track whether we have a writable mapping and unmap
only if we do.

[lstoakes@gmail.com: do not set writable_file_mapping in inappropriate case]
  Link: https://lkml.kernel.org/r/c9eb4cc6-7db4-4c2b-838d-43a0b319a4f0@lucifer.local
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238
Link: https://lkml.kernel.org/r/55e413d20678a1bb4c7cce889062bbb07b0df892.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
[isaacmanjarres: added error handling to cleanup the work done by the
mmap() callback and removed unused label.]
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/mmap.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1718,6 +1718,7 @@ unsigned long mmap_region(struct file *f
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
+	bool writable_file_mapping = false;
 	int error;
 	struct rb_node **rb_link, *rb_parent;
 	unsigned long charged = 0;
@@ -1785,11 +1786,6 @@ unsigned long mmap_region(struct file *f
 			if (error)
 				goto free_vma;
 		}
-		if (is_shared_maywrite(vm_flags)) {
-			error = mapping_map_writable(file->f_mapping);
-			if (error)
-				goto allow_write_and_free_vma;
-		}
 
 		/* ->mmap() can change vma->vm_file, but must guarantee that
 		 * vma_link() below can deny write-access if VM_DENYWRITE is set
@@ -1801,6 +1797,14 @@ unsigned long mmap_region(struct file *f
 		if (error)
 			goto unmap_and_free_vma;
 
+		if (vma_is_shared_maywrite(vma)) {
+			error = mapping_map_writable(file->f_mapping);
+			if (error)
+				goto close_and_free_vma;
+
+			writable_file_mapping = true;
+		}
+
 		/* Can addr have changed??
 		 *
 		 * Answer: Yes, several device drivers can do it in their
@@ -1823,7 +1827,7 @@ unsigned long mmap_region(struct file *f
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	/* Once vma denies write, undo our temporary denial count */
 	if (file) {
-		if (is_shared_maywrite(vm_flags))
+		if (writable_file_mapping)
 			mapping_unmap_writable(file->f_mapping);
 		if (vm_flags & VM_DENYWRITE)
 			allow_write_access(file);
@@ -1858,15 +1862,17 @@ out:
 
 	return addr;
 
+close_and_free_vma:
+	if (vma->vm_ops && vma->vm_ops->close)
+		vma->vm_ops->close(vma);
 unmap_and_free_vma:
 	vma->vm_file = NULL;
 	fput(file);
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
-	if (is_shared_maywrite(vm_flags))
+	if (writable_file_mapping)
 		mapping_unmap_writable(file->f_mapping);
-allow_write_and_free_vma:
 	if (vm_flags & VM_DENYWRITE)
 		allow_write_access(file);
 free_vma:


Patches currently in stable-queue which might be from isaacmanjarres@google.com are

queue-5.4/mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
queue-5.4/mm-perform-the-mapping_map_writable-check-after-call_mmap.patch
queue-5.4/mm-update-memfd-seal-write-check-to-include-f_seal_write.patch

Patch "mm: update memfd seal write check to include F_SEAL_WRITE" has been added to the 5.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm: update memfd seal write check to include F_SEAL_WRITE

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-update-memfd-seal-write-check-to-include-f_seal_write.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-165154-greg=kroah.com@vger.kernel.org Wed Jul 30 02:59:10 2025
From: "Isaac J. Manjarres" <isaacmanjarres@google.com>
Date: Tue, 29 Jul 2025 17:58:07 -0700
Subject: mm: update memfd seal write check to include F_SEAL_WRITE
To: lorenzo.stoakes@oracle.com, gregkh@linuxfoundation.org,  Muchun Song <muchun.song@linux.dev>, Oscar Salvador <osalvador@suse.de>,  David Hildenbrand <david@redhat.com>, Alexander Viro <viro@zeniv.linux.org.uk>,  Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,  Andrew Morton <akpm@linux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@oracle.com>,  Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>, Suren Baghdasaryan <surenb@google.com>,  Michal Hocko <mhocko@suse.com>, Kees Cook <kees@kernel.org>, Ingo Molnar <mingo@redhat.com>,  Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>,  Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>,  Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,  Valentin Schneider <vschneid@redhat.com>, "Matthew Wilcox (Oracle)" <willy@infradead.org>, Jann Horn <jannh@google.com>,  Pedro Falcato <pfalcato@s
 use.de>,
  Hugh Dickins <hughd@google.com>,  Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: aliceryhl@google.com, stable@vger.kernel.org,  "Isaac J. Manjarres" <isaacmanjarres@google.com>, kernel-team@android.com, linux-mm@kvack.org,  linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,  Lorenzo Stoakes <lstoakes@gmail.com>, Andy Lutomirski <luto@kernel.org>,  Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <20250730005818.2793577-3-isaacmanjarres@google.com>

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 28464bbb2ddc199433383994bcb9600c8034afa1 ]

The seal_check_future_write() function is called by shmem_mmap() or
hugetlbfs_file_mmap() to disallow any future writable mappings of an memfd
sealed this way.

The F_SEAL_WRITE flag is not checked here, as that is handled via the
mapping->i_mmap_writable mechanism and so any attempt at a mapping would
fail before this could be run.

However we intend to change this, meaning this check can be performed for
F_SEAL_WRITE mappings also.

The logic here is equally applicable to both flags, so update this
function to accommodate both and rename it accordingly.

Link: https://lkml.kernel.org/r/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/hugetlbfs/inode.c |    2 +-
 include/linux/mm.h   |   15 ++++++++-------
 mm/shmem.c           |    2 +-
 3 files changed, 10 insertions(+), 9 deletions(-)

--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -152,7 +152,7 @@ static int hugetlbfs_file_mmap(struct fi
 	vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
 	vma->vm_ops = &hugetlb_vm_ops;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2946,25 +2946,26 @@ static inline int pages_identical(struct
 }
 
 /**
- * seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it
+ * seal_check_write - Check for F_SEAL_WRITE or F_SEAL_FUTURE_WRITE flags and
+ *                    handle them.
  * @seals: the seals to check
  * @vma: the vma to operate on
  *
- * Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on
- * the vma flags.  Return 0 if check pass, or <0 for errors.
+ * Check whether F_SEAL_WRITE or F_SEAL_FUTURE_WRITE are set; if so, do proper
+ * check/handling on the vma flags.  Return 0 if check pass, or <0 for errors.
  */
-static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
+static inline int seal_check_write(int seals, struct vm_area_struct *vma)
 {
-	if (seals & F_SEAL_FUTURE_WRITE) {
+	if (seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
 		/*
 		 * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
-		 * "future write" seal active.
+		 * write seals are active.
 		 */
 		if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
 			return -EPERM;
 
 		/*
-		 * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as
+		 * Since an F_SEAL_[FUTURE_]WRITE sealed memfd can be mapped as
 		 * MAP_SHARED and read-only, take care to not allow mprotect to
 		 * revert protections on such mappings. Do this only for shared
 		 * mappings. For private mappings, don't need to mask
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2215,7 +2215,7 @@ static int shmem_mmap(struct file *file,
 	struct shmem_inode_info *info = SHMEM_I(file_inode(file));
 	int ret;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 


Patches currently in stable-queue which might be from isaacmanjarres@google.com are

queue-5.4/mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
queue-5.4/mm-perform-the-mapping_map_writable-check-after-call_mmap.patch
queue-5.4/mm-update-memfd-seal-write-check-to-include-f_seal_write.patch

Patch "mm: drop the assumption that VM_SHARED always implies writable" has been added to the 5.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm: drop the assumption that VM_SHARED always implies writable

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-165153-greg=kroah.com@vger.kernel.org Wed Jul 30 02:58:50 2025
From: "Isaac J. Manjarres" <isaacmanjarres@google.com>
Date: Tue, 29 Jul 2025 17:58:06 -0700
Subject: mm: drop the assumption that VM_SHARED always implies writable
To: lorenzo.stoakes@oracle.com, gregkh@linuxfoundation.org,  Muchun Song <muchun.song@linux.dev>, Oscar Salvador <osalvador@suse.de>,  David Hildenbrand <david@redhat.com>, Alexander Viro <viro@zeniv.linux.org.uk>,  Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,  Andrew Morton <akpm@linux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@oracle.com>,  Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>, Suren Baghdasaryan <surenb@google.com>,  Michal Hocko <mhocko@suse.com>, Kees Cook <kees@kernel.org>, Ingo Molnar <mingo@redhat.com>,  Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>,  Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>,  Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,  Valentin Schneider <vschneid@redhat.com>, "Matthew Wilcox (Oracle)" <willy@infradead.org>, Jann Horn <jannh@google.com>,  Pedro Falcato <pfalcato@s
 use.de>,
  Hugh Dickins <hughd@google.com>,  Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: aliceryhl@google.com, stable@vger.kernel.org,  "Isaac J. Manjarres" <isaacmanjarres@google.com>, kernel-team@android.com, linux-mm@kvack.org,  linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,  Lorenzo Stoakes <lstoakes@gmail.com>, Andy Lutomirski <luto@kernel.org>,  Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <20250730005818.2793577-2-isaacmanjarres@google.com>

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit e8e17ee90eaf650c855adb0a3e5e965fd6692ff1 ]

Patch series "permit write-sealed memfd read-only shared mappings", v4.

The man page for fcntl() describing memfd file seals states the following
about F_SEAL_WRITE:-

    Furthermore, trying to create new shared, writable memory-mappings via
    mmap(2) will also fail with EPERM.

With emphasis on 'writable'.  In turns out in fact that currently the
kernel simply disallows all new shared memory mappings for a memfd with
F_SEAL_WRITE applied, rendering this documentation inaccurate.

This matters because users are therefore unable to obtain a shared mapping
to a memfd after write sealing altogether, which limits their usefulness.
This was reported in the discussion thread [1] originating from a bug
report [2].

This is a product of both using the struct address_space->i_mmap_writable
atomic counter to determine whether writing may be permitted, and the
kernel adjusting this counter when any VM_SHARED mapping is performed and
more generally implicitly assuming VM_SHARED implies writable.

It seems sensible that we should only update this mapping if VM_MAYWRITE
is specified, i.e.  whether it is possible that this mapping could at any
point be written to.

If we do so then all we need to do to permit write seals to function as
documented is to clear VM_MAYWRITE when mapping read-only.  It turns out
this functionality already exists for F_SEAL_FUTURE_WRITE - we can
therefore simply adapt this logic to do the same for F_SEAL_WRITE.

We then hit a chicken and egg situation in mmap_region() where the check
for VM_MAYWRITE occurs before we are able to clear this flag.  To work
around this, perform this check after we invoke call_mmap(), with careful
consideration of error paths.

Thanks to Andy Lutomirski for the suggestion!

[1]:https://lore.kernel.org/all/20230324133646.16101dfa666f253c4715d965@linux-foundation.org/
[2]:https://bugzilla.kernel.org/show_bug.cgi?id=217238

This patch (of 3):

There is a general assumption that VMAs with the VM_SHARED flag set are
writable.  If the VM_MAYWRITE flag is not set, then this is simply not the
case.

Update those checks which affect the struct address_space->i_mmap_writable
field to explicitly test for this by introducing
[vma_]is_shared_maywrite() helper functions.

This remains entirely conservative, as the lack of VM_MAYWRITE guarantees
that the VMA cannot be written to.

Link: https://lkml.kernel.org/r/cover.1697116581.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/d978aefefa83ec42d18dfa964ad180dbcde34795.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/fs.h |    4 ++--
 include/linux/mm.h |   11 +++++++++++
 kernel/fork.c      |    2 +-
 mm/filemap.c       |    2 +-
 mm/madvise.c       |    2 +-
 mm/mmap.c          |   10 +++++-----
 6 files changed, 21 insertions(+), 10 deletions(-)

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -430,7 +430,7 @@ int pagecache_write_end(struct file *, s
  * @host: Owner, either the inode or the block_device.
  * @i_pages: Cached pages.
  * @gfp_mask: Memory allocation flags to use for allocating pages.
- * @i_mmap_writable: Number of VM_SHARED mappings.
+ * @i_mmap_writable: Number of VM_SHARED, VM_MAYWRITE mappings.
  * @nr_thps: Number of THPs in the pagecache (non-shmem only).
  * @i_mmap: Tree of private and shared mappings.
  * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable.
@@ -553,7 +553,7 @@ static inline int mapping_mapped(struct
 
 /*
  * Might pages of this file have been modified in userspace?
- * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap_pgoff
+ * Note that i_mmap_writable counts all VM_SHARED, VM_MAYWRITE vmas: do_mmap_pgoff
  * marks vma as VM_SHARED if it is shared, and the file was opened for
  * writing i.e. vma may be mprotected writable even if now readonly.
  *
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -549,6 +549,17 @@ static inline bool vma_is_anonymous(stru
 	return !vma->vm_ops;
 }
 
+static inline bool is_shared_maywrite(vm_flags_t vm_flags)
+{
+	return (vm_flags & (VM_SHARED | VM_MAYWRITE)) ==
+		(VM_SHARED | VM_MAYWRITE);
+}
+
+static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma)
+{
+	return is_shared_maywrite(vma->vm_flags);
+}
+
 #ifdef CONFIG_SHMEM
 /*
  * The vma_is_shmem is not inline because it is used only by slow
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -566,7 +566,7 @@ static __latent_entropy int dup_mmap(str
 			if (tmp->vm_flags & VM_DENYWRITE)
 				atomic_dec(&inode->i_writecount);
 			i_mmap_lock_write(mapping);
-			if (tmp->vm_flags & VM_SHARED)
+			if (vma_is_shared_maywrite(tmp))
 				atomic_inc(&mapping->i_mmap_writable);
 			flush_dcache_mmap_lock(mapping);
 			/* insert tmp into the share list, just after mpnt */
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2876,7 +2876,7 @@ int generic_file_mmap(struct file * file
  */
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+	if (vma_is_shared_maywrite(vma))
 		return -EINVAL;
 	return generic_file_mmap(file, vma);
 }
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -839,7 +839,7 @@ static long madvise_remove(struct vm_are
 			return -EINVAL;
 	}
 
-	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
+	if (!vma_is_shared_maywrite(vma))
 		return -EACCES;
 
 	offset = (loff_t)(start - vma->vm_start)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -141,7 +141,7 @@ static void __remove_shared_vm_struct(st
 {
 	if (vma->vm_flags & VM_DENYWRITE)
 		atomic_inc(&file_inode(file)->i_writecount);
-	if (vma->vm_flags & VM_SHARED)
+	if (vma_is_shared_maywrite(vma))
 		mapping_unmap_writable(mapping);
 
 	flush_dcache_mmap_lock(mapping);
@@ -619,7 +619,7 @@ static void __vma_link_file(struct vm_ar
 
 		if (vma->vm_flags & VM_DENYWRITE)
 			atomic_dec(&file_inode(file)->i_writecount);
-		if (vma->vm_flags & VM_SHARED)
+		if (vma_is_shared_maywrite(vma))
 			atomic_inc(&mapping->i_mmap_writable);
 
 		flush_dcache_mmap_lock(mapping);
@@ -1785,7 +1785,7 @@ unsigned long mmap_region(struct file *f
 			if (error)
 				goto free_vma;
 		}
-		if (vm_flags & VM_SHARED) {
+		if (is_shared_maywrite(vm_flags)) {
 			error = mapping_map_writable(file->f_mapping);
 			if (error)
 				goto allow_write_and_free_vma;
@@ -1823,7 +1823,7 @@ unsigned long mmap_region(struct file *f
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	/* Once vma denies write, undo our temporary denial count */
 	if (file) {
-		if (vm_flags & VM_SHARED)
+		if (is_shared_maywrite(vm_flags))
 			mapping_unmap_writable(file->f_mapping);
 		if (vm_flags & VM_DENYWRITE)
 			allow_write_access(file);
@@ -1864,7 +1864,7 @@ unmap_and_free_vma:
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
-	if (vm_flags & VM_SHARED)
+	if (is_shared_maywrite(vm_flags))
 		mapping_unmap_writable(file->f_mapping);
 allow_write_and_free_vma:
 	if (vm_flags & VM_DENYWRITE)


Patches currently in stable-queue which might be from isaacmanjarres@google.com are

queue-5.4/mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
queue-5.4/mm-perform-the-mapping_map_writable-check-after-call_mmap.patch
queue-5.4/mm-update-memfd-seal-write-check-to-include-f_seal_write.patch