From: Anthony Yznaga Date: Tue, 10 Mar 2026 15:58:20 +0000 (-0700) Subject: mm: prevent droppable mappings from being locked X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d239462787b072c78eb19fc1f155c3d411256282;p=thirdparty%2Fkernel%2Flinux.git mm: prevent droppable mappings from being locked Droppable mappings must not be lockable. There is a check for VMAs with VM_DROPPABLE set in mlock_fixup() along with checks for other types of unlockable VMAs which ensures this when calling mlock()/mlock2(). For mlockall(MCL_FUTURE), the check for unlockable VMAs is different. In apply_mlockall_flags(), if the flags parameter has MCL_FUTURE set, the current task's mm's default VMA flag field mm->def_flags has VM_LOCKED applied to it. VM_LOCKONFAULT is also applied if MCL_ONFAULT is also set. When these flags are set as default in this manner they are cleared in __mmap_complete() for new mappings that do not support mlock. A check for VM_DROPPABLE in __mmap_complete() is missing resulting in droppable mappings created with VM_LOCKED set. To fix this and reduce that chance of similar bugs in the future, introduce and use vma_supports_mlock(). Link: https://lkml.kernel.org/r/20260310155821.17869-1-anthony.yznaga@oracle.com Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings") Signed-off-by: Anthony Yznaga Suggested-by: David Hildenbrand Acked-by: David Hildenbrand (Arm) Reviewed-by: Pedro Falcato Reviewed-by: Lorenzo Stoakes (Oracle) Tested-by: Lorenzo Stoakes (Oracle) Cc: Jann Horn Cc: Jason A. Donenfeld Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- diff --git a/include/linux/hugetlb_inline.h b/include/linux/hugetlb_inline.h index 84afc3c3e2e4b..565b473fd1353 100644 --- a/include/linux/hugetlb_inline.h +++ b/include/linux/hugetlb_inline.h @@ -30,7 +30,7 @@ static inline bool is_vma_hugetlb_flags(const vma_flags_t *flags) #endif -static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma) +static inline bool is_vm_hugetlb_page(const struct vm_area_struct *vma) { return is_vm_hugetlb_flags(vma->vm_flags); } diff --git a/mm/internal.h b/mm/internal.h index 4ab833b8bcdf5..ebb68ad10d5c7 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1243,6 +1243,16 @@ static inline struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf, } return fpin; } + +static inline bool vma_supports_mlock(const struct vm_area_struct *vma) +{ + if (vma->vm_flags & (VM_SPECIAL | VM_DROPPABLE)) + return false; + if (vma_is_dax(vma) || is_vm_hugetlb_page(vma)) + return false; + return vma != get_gate_vma(current->mm); +} + #else /* !CONFIG_MMU */ static inline void unmap_mapping_folio(struct folio *folio) { } static inline void mlock_new_folio(struct folio *folio) { } diff --git a/mm/mlock.c b/mm/mlock.c index 1a92d16f36847..fd648138bc72e 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -472,10 +472,12 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma, int ret = 0; vm_flags_t oldflags = vma->vm_flags; - if (newflags == oldflags || (oldflags & VM_SPECIAL) || - is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) || - vma_is_dax(vma) || vma_is_secretmem(vma) || (oldflags & VM_DROPPABLE)) - /* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */ + if (newflags == oldflags || vma_is_secretmem(vma) || + !vma_supports_mlock(vma)) + /* + * Don't set VM_LOCKED or VM_LOCKONFAULT and don't count. + * For secretmem, don't allow the memory to be unlocked. + */ goto out; vma = vma_modify_flags(vmi, *prev, vma, start, end, &newflags); diff --git a/mm/vma.c b/mm/vma.c index e95fd5a5fe5c6..b7055c264b5d3 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2589,9 +2589,7 @@ static void __mmap_complete(struct mmap_state *map, struct vm_area_struct *vma) vm_stat_account(mm, vma->vm_flags, map->pglen); if (vm_flags & VM_LOCKED) { - if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) || - is_vm_hugetlb_page(vma) || - vma == get_gate_vma(mm)) + if (!vma_supports_mlock(vma)) vm_flags_clear(vma, VM_LOCKED_MASK); else mm->locked_vm += map->pglen; diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h index 947a3a0c25665..416bb93f50053 100644 --- a/tools/testing/vma/include/stubs.h +++ b/tools/testing/vma/include/stubs.h @@ -426,3 +426,8 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, } static inline void hugetlb_split(struct vm_area_struct *, unsigned long) {} + +static inline bool vma_supports_mlock(const struct vm_area_struct *vma) +{ + return false; +}