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a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=dt9VzEwgFbYA:10 a=GoEa3M9JfhUA:10 a=yPCof4ZbAAAA:8 a=BnYvykHrKgfMS8ox0bgA:9 X-Proofpoint-GUID: u1rnVcs5m-ZqMZqoWszTXfD9CR5a-X6v X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTA5MDExOCBTYWx0ZWRfX4fvf5Ti8RQu9 6PFfeJZ0OGy9Vh/zbKGo7PCgI+GdazeI0hCrEwH1PzDKKMW0sW/re2u217dAuCwUX72y3DUIJjo 0+DKxvrh5Fx1nwL/NLei2BwDQKZnhULNAasVkXQhhXpP/TdOjw19yHCwldozW0tUwF9my2Z9cL0 g0UlQT2b3YX+kKgb24BW8CvM8cfet96wYVmdvQ4KVDX4iKmJB4XE4wSuM9qK0hts9FU4b+zwDYq DUk8GD9+pxPoJHDRLIa7QUyIphqVCNa9RrGW3HamaT4QwIj7S1E0/4rqQs0R2B/MEy1StbB4hJ6 tgDiMnDJly+B9NLqRGHMF++iN9PXbTLd2zwDPux1PeKIPbN8ubASjwi54pV52JYrQqrli1Kkoad YekualPrA+svhXFdoDB+NHL6dkWx4+/M/cRtEmnowILG37ZmPR3tIZrQoMkaZKPW/cPsewaT X-Proofpoint-ORIG-GUID: u1rnVcs5m-ZqMZqoWszTXfD9CR5a-X6v Content-Type: text/plain; charset="utf-8" Provide a means by which drivers can specify which fields of those permitted to be changed should be altered to prior to mmap()'ing a range (which may either result from a merge or from mapping an entirely new VMA). Doing so is substantially safer than the existing .mmap() calback which provides unrestricted access to the part-constructed VMA and permits drivers and file systems to do 'creative' things which makes it hard to reason about the state of the VMA after the function returns. The existing .mmap() callback's freedom has caused a great deal of issues, especially in error handling, as unwinding the mmap() state has proven to be non-trivial and caused significant issues in the past, for instance those addressed in commit 5de195060b2e ("mm: resolve faulty mmap_region() error path behaviour"). It also necessitates a second attempt at merge once the .mmap() callback has completed, which has caused issues in the past, is awkward, adds overhead and is difficult to reason about. The .mmap_prepare() callback eliminates this requirement, as we can update fields prior to even attempting the first merge. It is safer, as we heavily restrict what can actually be modified, and being invoked very early in the mmap() process, error handling can be performed safely with very little unwinding of state required. The .mmap_prepare() and deprecated .mmap() callbacks are mutually exclusive, so we permit only one to be invoked at a time. Update vma userland test stubs to account for changes. Signed-off-by: Lorenzo Stoakes Reviewed-by: Liam R. Howlett Reviewed-by: Pedro Falcato Reviewed-by: Suren Baghdasaryan Reviewed-by: Vlastimil Babka --- include/linux/fs.h | 25 ++++++++++++ include/linux/mm_types.h | 24 +++++++++++ mm/memory.c | 3 +- mm/mmap.c | 2 +- mm/vma.c | 68 +++++++++++++++++++++++++++++++- tools/testing/vma/vma_internal.h | 66 ++++++++++++++++++++++++++++--- 6 files changed, 180 insertions(+), 8 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 016b0fe1536e..e2721a1ff13d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2169,6 +2169,7 @@ struct file_operations { int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags); int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *, unsigned int poll_flags); + int (*mmap_prepare)(struct vm_area_desc *); } __randomize_layout; =20 /* Supports async buffered reads */ @@ -2238,11 +2239,35 @@ struct inode_operations { struct offset_ctx *(*get_offset_ctx)(struct inode *inode); } ____cacheline_aligned; =20 +/* Did the driver provide valid mmap hook configuration? */ +static inline bool file_has_valid_mmap_hooks(struct file *file) +{ + bool has_mmap =3D file->f_op->mmap; + bool has_mmap_prepare =3D file->f_op->mmap_prepare; + + /* Hooks are mutually exclusive. */ + if (WARN_ON_ONCE(has_mmap && has_mmap_prepare)) + return false; + if (WARN_ON_ONCE(!has_mmap && !has_mmap_prepare)) + return false; + + return true; +} + static inline int call_mmap(struct file *file, struct vm_area_struct *vma) { + if (WARN_ON_ONCE(file->f_op->mmap_prepare)) + return -EINVAL; + return file->f_op->mmap(file, vma); } =20 +static inline int __call_mmap_prepare(struct file *file, + struct vm_area_desc *desc) +{ + return file->f_op->mmap_prepare(desc); +} + extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *); extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_= t *); extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *, diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index e76bade9ebb1..15808cad2bc1 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -763,6 +763,30 @@ struct vma_numab_state { int prev_scan_seq; }; =20 +/* + * Describes a VMA that is about to be mmap()'ed. Drivers may choose to + * manipulate mutable fields which will cause those fields to be updated i= n the + * resultant VMA. + * + * Helper functions are not required for manipulating any field. + */ +struct vm_area_desc { + /* Immutable state. */ + struct mm_struct *mm; + unsigned long start; + unsigned long end; + + /* Mutable fields. Populated with initial state. */ + pgoff_t pgoff; + struct file *file; + vm_flags_t vm_flags; + pgprot_t page_prot; + + /* Write-only fields. */ + const struct vm_operations_struct *vm_ops; + void *private_data; +}; + /* * This struct describes a virtual memory area. There is one of these * per VM-area/task. A VM area is any part of the process virtual memory diff --git a/mm/memory.c b/mm/memory.c index 68c1d962d0ad..99af83434e7c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -527,10 +527,11 @@ static void print_bad_pte(struct vm_area_struct *vma,= unsigned long addr, dump_page(page, "bad pte"); pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n", (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index); - pr_alert("file:%pD fault:%ps mmap:%ps read_folio:%ps\n", + pr_alert("file:%pD fault:%ps mmap:%ps mmap_prepare: %ps read_folio:%ps\n", vma->vm_file, vma->vm_ops ? vma->vm_ops->fault : NULL, vma->vm_file ? vma->vm_file->f_op->mmap : NULL, + vma->vm_file ? vma->vm_file->f_op->mmap_prepare : NULL, mapping ? mapping->a_ops->read_folio : NULL); dump_stack(); add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); diff --git a/mm/mmap.c b/mm/mmap.c index 81dd962a1cfc..50f902c08341 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -475,7 +475,7 @@ unsigned long do_mmap(struct file *file, unsigned long = addr, vm_flags &=3D ~VM_MAYEXEC; } =20 - if (!file->f_op->mmap) + if (!file_has_valid_mmap_hooks(file)) return -ENODEV; if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)) return -EINVAL; diff --git a/mm/vma.c b/mm/vma.c index 1f2634b29568..3f32e04bb6cc 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -17,6 +17,11 @@ struct mmap_state { unsigned long pglen; unsigned long flags; struct file *file; + pgprot_t page_prot; + + /* User-defined fields, perhaps updated by .mmap_prepare(). */ + const struct vm_operations_struct *vm_ops; + void *vm_private_data; =20 unsigned long charged; bool retry_merge; @@ -40,6 +45,7 @@ struct mmap_state { .pglen =3D PHYS_PFN(len_), \ .flags =3D flags_, \ .file =3D file_, \ + .page_prot =3D vm_get_page_prot(flags_), \ } =20 #define VMG_MMAP_STATE(name, map_, vma_) \ @@ -2385,6 +2391,10 @@ static int __mmap_new_file_vma(struct mmap_state *ma= p, int error; =20 vma->vm_file =3D get_file(map->file); + + if (!map->file->f_op->mmap) + return 0; + error =3D mmap_file(vma->vm_file, vma); if (error) { fput(vma->vm_file); @@ -2441,7 +2451,7 @@ static int __mmap_new_vma(struct mmap_state *map, str= uct vm_area_struct **vmap) vma_iter_config(vmi, map->addr, map->end); vma_set_range(vma, map->addr, map->end, map->pgoff); vm_flags_init(vma, map->flags); - vma->vm_page_prot =3D vm_get_page_prot(map->flags); + vma->vm_page_prot =3D map->page_prot; =20 if (vma_iter_prealloc(vmi, vma)) { error =3D -ENOMEM; @@ -2528,6 +2538,56 @@ static void __mmap_complete(struct mmap_state *map, = struct vm_area_struct *vma) vma_set_page_prot(vma); } =20 +/* + * Invoke the f_op->mmap_prepare() callback for a file-backed mapping that + * specifies it. + * + * This is called prior to any merge attempt, and updates whitelisted fiel= ds + * that are permitted to be updated by the caller. + * + * All but user-defined fields will be pre-populated with original values. + * + * Returns 0 on success, or an error code otherwise. + */ +static int call_mmap_prepare(struct mmap_state *map) +{ + int err; + struct vm_area_desc desc =3D { + .mm =3D map->mm, + .start =3D map->addr, + .end =3D map->end, + + .pgoff =3D map->pgoff, + .file =3D map->file, + .vm_flags =3D map->flags, + .page_prot =3D map->page_prot, + }; + + /* Invoke the hook. */ + err =3D __call_mmap_prepare(map->file, &desc); + if (err) + return err; + + /* Update fields permitted to be changed. */ + map->pgoff =3D desc.pgoff; + map->file =3D desc.file; + map->flags =3D desc.vm_flags; + map->page_prot =3D desc.page_prot; + /* User-defined fields. */ + map->vm_ops =3D desc.vm_ops; + map->vm_private_data =3D desc.private_data; + + return 0; +} + +static void set_vma_user_defined_fields(struct vm_area_struct *vma, + struct mmap_state *map) +{ + if (map->vm_ops) + vma->vm_ops =3D map->vm_ops; + vma->vm_private_data =3D map->vm_private_data; +} + static unsigned long __mmap_region(struct file *file, unsigned long addr, unsigned long len, vm_flags_t vm_flags, unsigned long pgoff, struct list_head *uf) @@ -2535,10 +2595,13 @@ static unsigned long __mmap_region(struct file *fil= e, unsigned long addr, struct mm_struct *mm =3D current->mm; struct vm_area_struct *vma =3D NULL; int error; + bool have_mmap_prepare =3D file && file->f_op->mmap_prepare; VMA_ITERATOR(vmi, mm, addr); MMAP_STATE(map, mm, &vmi, addr, len, pgoff, vm_flags, file); =20 error =3D __mmap_prepare(&map, uf); + if (!error && have_mmap_prepare) + error =3D call_mmap_prepare(&map); if (error) goto abort_munmap; =20 @@ -2556,6 +2619,9 @@ static unsigned long __mmap_region(struct file *file,= unsigned long addr, goto unacct_error; } =20 + if (have_mmap_prepare) + set_vma_user_defined_fields(vma, &map); + /* If flags changed, we might be able to merge, so try again. */ if (map.retry_merge) { struct vm_area_struct *merged; diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_inter= nal.h index 198abe66de5a..f6e45e62da3a 100644 --- a/tools/testing/vma/vma_internal.h +++ b/tools/testing/vma/vma_internal.h @@ -253,8 +253,40 @@ struct mm_struct { unsigned long flags; /* Must use atomic bitops to access */ }; =20 +struct vm_area_struct; + +/* + * Describes a VMA that is about to be mmap()'ed. Drivers may choose to + * manipulate mutable fields which will cause those fields to be updated i= n the + * resultant VMA. + * + * Helper functions are not required for manipulating any field. + */ +struct vm_area_desc { + /* Immutable state. */ + struct mm_struct *mm; + unsigned long start; + unsigned long end; + + /* Mutable fields. Populated with initial state. */ + pgoff_t pgoff; + struct file *file; + vm_flags_t vm_flags; + pgprot_t page_prot; + + /* Write-only fields. */ + const struct vm_operations_struct *vm_ops; + void *private_data; +}; + +struct file_operations { + int (*mmap)(struct file *, struct vm_area_struct *); + int (*mmap_prepare)(struct vm_area_desc *); +}; + struct file { struct address_space *f_mapping; + const struct file_operations *f_op; }; =20 #define VMA_LOCK_OFFSET 0x40000000 @@ -1125,11 +1157,6 @@ static inline void vm_flags_clear(struct vm_area_str= uct *vma, vma->__vm_flags &=3D ~flags; } =20 -static inline int call_mmap(struct file *, struct vm_area_struct *) -{ - return 0; -} - static inline int shmem_zero_setup(struct vm_area_struct *) { return 0; @@ -1405,4 +1432,33 @@ static inline void free_anon_vma_name(struct vm_area= _struct *vma) (void)vma; } =20 +/* Did the driver provide valid mmap hook configuration? */ +static inline bool file_has_valid_mmap_hooks(struct file *file) +{ + bool has_mmap =3D file->f_op->mmap; + bool has_mmap_prepare =3D file->f_op->mmap_prepare; + + /* Hooks are mutually exclusive. */ + if (WARN_ON_ONCE(has_mmap && has_mmap_prepare)) + return false; + if (WARN_ON_ONCE(!has_mmap && !has_mmap_prepare)) + return false; + + return true; +} + +static inline int call_mmap(struct file *file, struct vm_area_struct *vma) +{ + if (WARN_ON_ONCE(file->f_op->mmap_prepare)) + return -EINVAL; + + return file->f_op->mmap(file, vma); +} + +static inline int __call_mmap_prepare(struct file *file, + struct vm_area_desc *desc) +{ + return file->f_op->mmap_prepare(desc); +} + #endif /* __MM_VMA_INTERNAL_H */ --=20 2.49.0