path: root/mm
diff options
authorPeter Xu <>2021-05-14 17:27:04 -0700
committerLinus Torvalds <>2021-05-14 19:41:32 -0700
commit22247efd822e6d263f3c8bd327f3f769aea9b1d9 (patch)
tree2bc99fea483cdffe7a0e114b629ab194c5aec04f /mm
parentbd3c9cdb21a2674dd0db70199df884828e37abd4 (diff)
mm/hugetlb: fix F_SEAL_FUTURE_WRITE
Patch series "mm/hugetlb: Fix issues on file sealing and fork", v2. Hugh reported issue with F_SEAL_FUTURE_WRITE not applied correctly to hugetlbfs, which I can easily verify using the memfd_test program, which seems that the program is hardly run with hugetlbfs pages (as by default shmem). Meanwhile I found another probably even more severe issue on that hugetlb fork won't wr-protect child cow pages, so child can potentially write to parent private pages. Patch 2 addresses that. After this series applied, "memfd_test hugetlbfs" should start to pass. This patch (of 2): F_SEAL_FUTURE_WRITE is missing for hugetlb starting from the first day. There is a test program for that and it fails constantly. $ ./memfd_test hugetlbfs memfd-hugetlb: CREATE memfd-hugetlb: BASIC memfd-hugetlb: SEAL-WRITE memfd-hugetlb: SEAL-FUTURE-WRITE mmap() didn't fail as expected Aborted (core dumped) I think it's probably because no one is really running the hugetlbfs test. Fix it by checking FUTURE_WRITE also in hugetlbfs_file_mmap() as what we do in shmem_mmap(). Generalize a helper for that. Link: Link: Fixes: ab3948f58ff84 ("mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd") Signed-off-by: Peter Xu <> Reported-by: Hugh Dickins <> Reviewed-by: Mike Kravetz <> Cc: Joel Fernandes (Google) <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
1 files changed, 4 insertions, 18 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index a08cedefbfaa..eb131b9fb190 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2258,25 +2258,11 @@ out_nomem:
static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
struct shmem_inode_info *info = SHMEM_I(file_inode(file));
+ int ret;
- if (info->seals & F_SEAL_FUTURE_WRITE) {
- /*
- * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
- * "future write" seal 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
- * 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
- * VM_MAYWRITE as we still want them to be COW-writable.
- */
- if (vma->vm_flags & VM_SHARED)
- vma->vm_flags &= ~(VM_MAYWRITE);
- }
+ ret = seal_check_future_write(info->seals, vma);
+ if (ret)
+ return ret;
/* arm64 - allow memory tagging on RAM-based files */
vma->vm_flags |= VM_MTE_ALLOWED;