Re: [PATCH 5.15.y 1/4] mm: drop the assumption that VM_SHARED always implies writable

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: e8e17ee90eaf650c855adb0a3e5e965fd6692ff1

WARNING: Author mismatch between patch and upstream commit:
Backport author: Isaac J. Manjarres <isaacmanjarres@google.com>
Commit author: Lorenzo Stoakes <lstoakes@gmail.com>

Status in newer kernel trees:
6.15.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Not found
6.1.y | Not found

Note: The patch differs from the upstream commit:
---
1:  e8e17ee90eaf ! 1:  9f7ea48b09ac mm: drop the assumption that VM_SHARED always implies writable
    @@ Metadata
      ## Commit message ##
         mm: drop the assumption that VM_SHARED always implies writable
     
    +    [ 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
    @@ Commit message
         [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
    @@ Commit message
         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: resolved merge conflicts due to
    +    due to refactoring that happened in upstream commit
    +    5de195060b2e ("mm: resolve faulty mmap_region() error path behaviour")]
    +    Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
     
      ## include/linux/fs.h ##
    -@@ include/linux/fs.h: extern const struct address_space_operations empty_aops;
    +@@ include/linux/fs.h: int pagecache_write_end(struct file *, struct address_space *mapping,
       *   It is also used to block modification of page cache contents through
       *   memory mappings.
       * @gfp_mask: Memory allocation flags to use for allocating pages.
    @@ include/linux/mm.h: static inline bool vma_is_accessible(struct vm_area_struct *
     +	return is_shared_maywrite(vma->vm_flags);
     +}
     +
    - static inline
    - struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max)
    - {
    + #ifdef CONFIG_SHMEM
    + /*
    +  * The vma_is_shmem is not inline because it is used only by slow
     
      ## kernel/fork.c ##
     @@ kernel/fork.c: static __latent_entropy int dup_mmap(struct mm_struct *mm,
    @@ mm/mmap.c: void vma_set_page_prot(struct vm_area_struct *vma)
      		mapping_unmap_writable(mapping);
      
      	flush_dcache_mmap_lock(mapping);
    -@@ mm/mmap.c: static unsigned long count_vma_pages_range(struct mm_struct *mm,
    - static void __vma_link_file(struct vm_area_struct *vma,
    - 			    struct address_space *mapping)
    - {
    --	if (vma->vm_flags & VM_SHARED)
    -+	if (vma_is_shared_maywrite(vma))
    - 		mapping_allow_writable(mapping);
    - 
    - 	flush_dcache_mmap_lock(mapping);
    -@@ mm/mmap.c: unsigned long mmap_region(struct file *file, unsigned long addr,
    - 	vma->vm_pgoff = pgoff;
    - 
    +@@ mm/mmap.c: static void __vma_link_file(struct vm_area_struct *vma)
      	if (file) {
    --		if (vm_flags & VM_SHARED) {
    -+		if (is_shared_maywrite(vm_flags)) {
    - 			error = mapping_map_writable(file->f_mapping);
    - 			if (error)
    - 				goto free_vma;
    -@@ mm/mmap.c: unsigned long mmap_region(struct file *file, unsigned long addr,
    - 	mm->map_count++;
    - 	if (vma->vm_file) {
    - 		i_mmap_lock_write(vma->vm_file->f_mapping);
    + 		struct address_space *mapping = file->f_mapping;
    + 
     -		if (vma->vm_flags & VM_SHARED)
     +		if (vma_is_shared_maywrite(vma))
    - 			mapping_allow_writable(vma->vm_file->f_mapping);
    + 			mapping_allow_writable(mapping);
      
    - 		flush_dcache_mmap_lock(vma->vm_file->f_mapping);
    + 		flush_dcache_mmap_lock(mapping);
     @@ mm/mmap.c: unsigned long mmap_region(struct file *file, unsigned long addr,
    + 		return -EINVAL;
      
    - 	/* Once vma denies write, undo our temporary denial count */
    - unmap_writable:
    --	if (file && vm_flags & VM_SHARED)
    -+	if (file && is_shared_maywrite(vm_flags))
    - 		mapping_unmap_writable(file->f_mapping);
    - 	file = vma->vm_file;
    - 	ksm_add_vma(vma);
    -@@ mm/mmap.c: unsigned long mmap_region(struct file *file, unsigned long addr,
    - 		unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start,
    - 			     vma->vm_end, vma->vm_end, true);
    - 	}
    --	if (file && (vm_flags & VM_SHARED))
    -+	if (file && is_shared_maywrite(vm_flags))
    - 		mapping_unmap_writable(file->f_mapping);
    - free_vma:
    - 	vm_area_free(vma);
    + 	/* Map writable and ensure this isn't a sealed memfd. */
    +-	if (file && (vm_flags & VM_SHARED)) {
    ++	if (file && is_shared_maywrite(vm_flags)) {
    + 		int error = mapping_map_writable(file->f_mapping);
    + 
    + 		if (error)

---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| 5.15                      | Success     | Success    |