mm: perform VMA allocation, freeing, duplication in mm

Right now these are performed in kernel/fork.c which is odd and a
violation of separation of concerns, as well as preventing us from
integrating this and related logic into userland VMA testing going
forward.

There is a fly in the ointment - nommu - mmap.c is not compiled if
CONFIG_MMU not set, and neither is vma.c.

To square the circle, let's add a new file - vma_init.c. This will be
compiled for both CONFIG_MMU and nommu builds, and will also form part of
the VMA userland testing.

This allows us to de-duplicate code, while maintaining separation of
concerns and the ability for us to userland test this logic.

Update the VMA userland tests accordingly, additionally adding a
detach_free_vma() helper function to correctly detach VMAs before freeing
them in test code, as this change was triggering the assert for this.

[[e-mail]: remove stray newline, per Liam]
Link: https://lkml.kernel.org/r/f97b3a8[e-mail]
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Reviewed-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Pedro Falcato <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Reviewed-by: Suren Baghdasaryan <[e-mail]>
Reviewed-by: Vlastimil Babka <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Jann Horn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

MAINTAINERS

···
 F:	mm/vma.c
 F:	mm/vma.h
 F:	mm/vma_exec.c
+F:	mm/vma_init.c
 F:	mm/vma_internal.h
 F:	tools/testing/selftests/mm/merge.c
 F:	tools/testing/vma/

kernel/fork.c

···
 /* SLAB cache for fs_struct structures (tsk->fs) */
 struct kmem_cache *fs_cachep;
 
-/* SLAB cache for vm_area_struct structures */
-static struct kmem_cache *vm_area_cachep;
-
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache *mm_cachep;
-
-struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
-{
-	struct vm_area_struct *vma;
-
-	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
-	if (!vma)
-		return NULL;
-
-	vma_init(vma, mm);
-
-	return vma;
-}
-
-static void vm_area_init_from(const struct vm_area_struct *src,
-			      struct vm_area_struct *dest)
-{
-	dest->vm_mm = src->vm_mm;
-	dest->vm_ops = src->vm_ops;
-	dest->vm_start = src->vm_start;
-	dest->vm_end = src->vm_end;
-	dest->anon_vma = src->anon_vma;
-	dest->vm_pgoff = src->vm_pgoff;
-	dest->vm_file = src->vm_file;
-	dest->vm_private_data = src->vm_private_data;
-	vm_flags_init(dest, src->vm_flags);
-	memcpy(&dest->vm_page_prot, &src->vm_page_prot,
-	       sizeof(dest->vm_page_prot));
-	/*
-	 * src->shared.rb may be modified concurrently when called from
-	 * dup_mmap(), but the clone will reinitialize it.
-	 */
-	data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
-	memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
-	       sizeof(dest->vm_userfaultfd_ctx));
-#ifdef CONFIG_ANON_VMA_NAME
-	dest->anon_name = src->anon_name;
-#endif
-#ifdef CONFIG_SWAP
-	memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
-	       sizeof(dest->swap_readahead_info));
-#endif
-#ifndef CONFIG_MMU
-	dest->vm_region = src->vm_region;
-#endif
-#ifdef CONFIG_NUMA
-	dest->vm_policy = src->vm_policy;
-#endif
-}
-
-struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
-{
-	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
-
-	if (!new)
-		return NULL;
-
-	ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
-	ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
-	vm_area_init_from(orig, new);
-	vma_lock_init(new, true);
-	INIT_LIST_HEAD(&new->anon_vma_chain);
-	vma_numab_state_init(new);
-	dup_anon_vma_name(orig, new);
-
-	return new;
-}
-
-void vm_area_free(struct vm_area_struct *vma)
-{
-	/* The vma should be detached while being destroyed. */
-	vma_assert_detached(vma);
-	vma_numab_state_free(vma);
-	free_anon_vma_name(vma);
-	kmem_cache_free(vm_area_cachep, vma);
-}
 
 static void account_kernel_stack(struct task_struct *tsk, int account)
 {
···
 
 void __init proc_caches_init(void)
 {
-	struct kmem_cache_args args = {
-		.use_freeptr_offset = true,
-		.freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr),
-	};
-
 	sighand_cachep = kmem_cache_create("sighand_cache",
 			sizeof(struct sighand_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
···
 			sizeof(struct fs_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
-	vm_area_cachep = kmem_cache_create("vm_area_struct",
-			sizeof(struct vm_area_struct), &args,
-			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
-			SLAB_ACCOUNT);
 	mmap_init();
 	nsproxy_cache_init();
 }

mm/Makefile

···
 			   mm_init.o percpu.o slab_common.o \
 			   compaction.o show_mem.o \
 			   interval_tree.o list_lru.o workingset.o \
-			   debug.o gup.o mmap_lock.o $(mmu-y)
+			   debug.o gup.o mmap_lock.o vma_init.o $(mmu-y)
 
 # Give 'page_alloc' its own module-parameter namespace
 page-alloc-y := page_alloc.o

mm/mmap.c

···
 #endif /* CONFIG_SYSCTL */
 
 /*
- * initialise the percpu counter for VM
+ * initialise the percpu counter for VM, initialise VMA state.
  */
 void __init mmap_init(void)
 {
···
 #ifdef CONFIG_SYSCTL
 	register_sysctl_init("vm", mmap_table);
 #endif
+	vma_state_init();
 }
 
 /*

mm/nommu.c

···
 };
 
 /*
- * initialise the percpu counter for VM and region record slabs
+ * initialise the percpu counter for VM and region record slabs, initialise VMA
+ * state.
  */
 void __init mmap_init(void)
 {
···
 	VM_BUG_ON(ret);
 	vm_region_jar = KMEM_CACHE(vm_region, SLAB_PANIC|SLAB_ACCOUNT);
 	register_sysctl_init("vm", nommu_table);
+	vma_state_init();
 }
 
 /*

mm/vma.h

···
 
 int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma);
 
+/* vma_init.h, shared between CONFIG_MMU and nommu. */
+void __init vma_state_init(void);
+struct vm_area_struct *vm_area_alloc(struct mm_struct *mm);
+struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig);
+void vm_area_free(struct vm_area_struct *vma);
+
 /* vma_exec.c */
 #ifdef CONFIG_MMU
 int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,

mm/vma_init.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * Functions for initialisaing, allocating, freeing and duplicating VMAs. Shared
+ * between CONFIG_MMU and non-CONFIG_MMU kernel configurations.
+ */
+
+#include "vma_internal.h"
+#include "vma.h"
+
+/* SLAB cache for vm_area_struct structures */
+static struct kmem_cache *vm_area_cachep;
+
+void __init vma_state_init(void)
+{
+	struct kmem_cache_args args = {
+		.use_freeptr_offset = true,
+		.freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr),
+	};
+
+	vm_area_cachep = kmem_cache_create("vm_area_struct",
+			sizeof(struct vm_area_struct), &args,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
+			SLAB_ACCOUNT);
+}
+
+struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+	if (!vma)
+		return NULL;
+
+	vma_init(vma, mm);
+
+	return vma;
+}
+
+static void vm_area_init_from(const struct vm_area_struct *src,
+			      struct vm_area_struct *dest)
+{
+	dest->vm_mm = src->vm_mm;
+	dest->vm_ops = src->vm_ops;
+	dest->vm_start = src->vm_start;
+	dest->vm_end = src->vm_end;
+	dest->anon_vma = src->anon_vma;
+	dest->vm_pgoff = src->vm_pgoff;
+	dest->vm_file = src->vm_file;
+	dest->vm_private_data = src->vm_private_data;
+	vm_flags_init(dest, src->vm_flags);
+	memcpy(&dest->vm_page_prot, &src->vm_page_prot,
+	       sizeof(dest->vm_page_prot));
+	/*
+	 * src->shared.rb may be modified concurrently when called from
+	 * dup_mmap(), but the clone will reinitialize it.
+	 */
+	data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
+	memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
+	       sizeof(dest->vm_userfaultfd_ctx));
+#ifdef CONFIG_ANON_VMA_NAME
+	dest->anon_name = src->anon_name;
+#endif
+#ifdef CONFIG_SWAP
+	memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
+	       sizeof(dest->swap_readahead_info));
+#endif
+#ifndef CONFIG_MMU
+	dest->vm_region = src->vm_region;
+#endif
+#ifdef CONFIG_NUMA
+	dest->vm_policy = src->vm_policy;
+#endif
+}
+
+struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
+{
+	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+
+	if (!new)
+		return NULL;
+
+	ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
+	ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
+	vm_area_init_from(orig, new);
+	vma_lock_init(new, true);
+	INIT_LIST_HEAD(&new->anon_vma_chain);
+	vma_numab_state_init(new);
+	dup_anon_vma_name(orig, new);
+
+	return new;
+}
+
+void vm_area_free(struct vm_area_struct *vma)
+{
+	/* The vma should be detached while being destroyed. */
+	vma_assert_detached(vma);
+	vma_numab_state_free(vma);
+	free_anon_vma_name(vma);
+	kmem_cache_free(vm_area_cachep, vma);
+}

tools/testing/vma/Makefile

···
 OFILES = $(SHARED_OFILES) vma.o maple-shim.o
 TARGETS = vma
 
-vma.o: vma.c vma_internal.h ../../../mm/vma.c ../../../mm/vma_exec.c ../../../mm/vma.h
+vma.o: vma.c vma_internal.h ../../../mm/vma.c ../../../mm/vma_init.c ../../../mm/vma_exec.c ../../../mm/vma.h
 
 vma:	$(OFILES)
 	$(CC) $(CFLAGS) -o $@ $(OFILES) $(LDLIBS)

tools/testing/vma/vma.c

···
  * Directly import the VMA implementation here. Our vma_internal.h wrapper
  * provides userland-equivalent functionality for everything vma.c uses.
  */
+#include "../../../mm/vma_init.c"
 #include "../../../mm/vma_exec.c"
 #include "../../../mm/vma.c"
 
···
 	return res;
 }
 
+static void detach_free_vma(struct vm_area_struct *vma)
+{
+	vma_mark_detached(vma);
+	vm_area_free(vma);
+}
+
 /* Helper function to allocate a VMA and link it to the tree. */
 static struct vm_area_struct *alloc_and_link_vma(struct mm_struct *mm,
 						 unsigned long start,
···
 		return NULL;
 
 	if (attach_vma(mm, vma)) {
-		vm_area_free(vma);
+		detach_free_vma(vma);
 		return NULL;
 	}
 
···
 
 	vma_iter_set(vmi, 0);
 	for_each_vma(*vmi, vma) {
-		vm_area_free(vma);
+		detach_free_vma(vma);
 		count++;
 	}
 
···
 	ASSERT_EQ(vma->vm_pgoff, 0);
 	ASSERT_EQ(vma->vm_flags, flags);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
 
 	return true;
···
 	ASSERT_EQ(vma->vm_end, 0x1000);
 	ASSERT_EQ(vma->vm_pgoff, 0);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	vma_iter_clear(&vmi);
 
 	vma = vma_next(&vmi);
···
 	ASSERT_EQ(vma->vm_end, 0x2000);
 	ASSERT_EQ(vma->vm_pgoff, 1);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	vma_iter_clear(&vmi);
 
 	vma = vma_next(&vmi);
···
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma->vm_pgoff, 2);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
 
 	return true;
···
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma->vm_pgoff, 0);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
 
 	return true;
···
 	ASSERT_EQ(vma->vm_end, 0x1000);
 	ASSERT_EQ(vma->vm_pgoff, 0);
 
-	vm_area_free(vma);
+	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
 
 	return true;
···
 		ASSERT_EQ(vma->vm_pgoff, 0);
 		ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 
-		vm_area_free(vma);
+		detach_free_vma(vma);
 		count++;
 	}
 
···
 	int num_tests = 0, num_fail = 0;
 
 	maple_tree_init();
+	vma_state_init();
 
 #define TEST(name)							\
 	do {								\

tools/testing/vma/vma_internal.h

···
  */
 #define pr_warn_once pr_err
 
+#define data_race(expr) expr
+
+#define ASSERT_EXCLUSIVE_WRITER(x)
+
 struct kref {
 	refcount_t refcount;
 };
···
 
 #define VMA_LOCK_OFFSET	0x40000000
 
+typedef struct { unsigned long v; } freeptr_t;
+
 struct vm_area_struct {
 	/* The first cache line has the info for VMA tree walking. */
 
···
 			unsigned long vm_start;
 			unsigned long vm_end;
 		};
-#ifdef CONFIG_PER_VMA_LOCK
-		struct rcu_head vm_rcu;	/* Used for deferred freeing. */
-#endif
+		freeptr_t vm_freeptr; /* Pointer used by SLAB_TYPESAFE_BY_RCU */
 	};
 
 	struct mm_struct *vm_mm;	/* The address space we belong to. */
···
 		.len_in = len_,						\
 	}
 
+struct kmem_cache_args {
+	/**
+	 * @align: The required alignment for the objects.
+	 *
+	 * %0 means no specific alignment is requested.
+	 */
+	unsigned int align;
+	/**
+	 * @useroffset: Usercopy region offset.
+	 *
+	 * %0 is a valid offset, when @usersize is non-%0
+	 */
+	unsigned int useroffset;
+	/**
+	 * @usersize: Usercopy region size.
+	 *
+	 * %0 means no usercopy region is specified.
+	 */
+	unsigned int usersize;
+	/**
+	 * @freeptr_offset: Custom offset for the free pointer
+	 * in &SLAB_TYPESAFE_BY_RCU caches
+	 *
+	 * By default &SLAB_TYPESAFE_BY_RCU caches place the free pointer
+	 * outside of the object. This might cause the object to grow in size.
+	 * Cache creators that have a reason to avoid this can specify a custom
+	 * free pointer offset in their struct where the free pointer will be
+	 * placed.
+	 *
+	 * Note that placing the free pointer inside the object requires the
+	 * caller to ensure that no fields are invalidated that are required to
+	 * guard against object recycling (See &SLAB_TYPESAFE_BY_RCU for
+	 * details).
+	 *
+	 * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset
+	 * is specified, %use_freeptr_offset must be set %true.
+	 *
+	 * Note that @ctor currently isn't supported with custom free pointers
+	 * as a @ctor requires an external free pointer.
+	 */
+	unsigned int freeptr_offset;
+	/**
+	 * @use_freeptr_offset: Whether a @freeptr_offset is used.
+	 */
+	bool use_freeptr_offset;
+	/**
+	 * @ctor: A constructor for the objects.
+	 *
+	 * The constructor is invoked for each object in a newly allocated slab
+	 * page. It is the cache user's responsibility to free object in the
+	 * same state as after calling the constructor, or deal appropriately
+	 * with any differences between a freshly constructed and a reallocated
+	 * object.
+	 *
+	 * %NULL means no constructor.
+	 */
+	void (*ctor)(void *);
+};
+
 static inline void vma_iter_invalidate(struct vma_iterator *vmi)
 {
 	mas_pause(&vmi->mas);
···
 	vma->vm_lock_seq = UINT_MAX;
 }
 
-static inline struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
+struct kmem_cache {
+	const char *name;
+	size_t object_size;
+	struct kmem_cache_args *args;
+};
+
+static inline struct kmem_cache *__kmem_cache_create(const char *name,
+						     size_t object_size,
+						     struct kmem_cache_args *args)
 {
-	struct vm_area_struct *vma = calloc(1, sizeof(struct vm_area_struct));
+	struct kmem_cache *ret = malloc(sizeof(struct kmem_cache));
 
-	if (!vma)
-		return NULL;
+	ret->name = name;
+	ret->object_size = object_size;
+	ret->args = args;
 
-	vma_init(vma, mm);
-
-	return vma;
+	return ret;
 }
 
-static inline struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
+#define kmem_cache_create(__name, __object_size, __args, ...)           \
+	__kmem_cache_create((__name), (__object_size), (__args))
+
+static inline void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
 {
-	struct vm_area_struct *new = calloc(1, sizeof(struct vm_area_struct));
+	(void)gfpflags;
 
-	if (!new)
-		return NULL;
+	return calloc(s->object_size, 1);
+}
 
-	memcpy(new, orig, sizeof(*new));
-	refcount_set(&new->vm_refcnt, 0);
-	new->vm_lock_seq = UINT_MAX;
-	INIT_LIST_HEAD(&new->anon_vma_chain);
-
-	return new;
+static inline void kmem_cache_free(struct kmem_cache *s, void *x)
+{
+	free(x);
 }
 
 /*
···
 
 static inline void mpol_put(struct mempolicy *)
 {
-}
-
-static inline void vm_area_free(struct vm_area_struct *vma)
-{
-	free(vma);
 }
 
 static inline void lru_add_drain(void)
···
 static inline void ksm_exit(struct mm_struct *mm)
 {
 	(void)mm;
+}
+
+static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt)
+{
+	(void)vma;
+	(void)reset_refcnt;
+}
+
+static inline void vma_numab_state_init(struct vm_area_struct *vma)
+{
+	(void)vma;
+}
+
+static inline void vma_numab_state_free(struct vm_area_struct *vma)
+{
+	(void)vma;
+}
+
+static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
+				     struct vm_area_struct *new_vma)
+{
+	(void)orig_vma;
+	(void)new_vma;
+}
+
+static inline void free_anon_vma_name(struct vm_area_struct *vma)
+{
+	(void)vma;
 }
 
 #endif	/* __MM_VMA_INTERNAL_H */