--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/err.h>
+#include <linux/btf_ids.h>
+#include <linux/vmalloc.h>
+#include <linux/pagemap.h>
+
+/*
+ * bpf_arena is a sparsely populated shared memory region between bpf program and
+ * user space process.
+ *
+ * For example on x86-64 the values could be:
+ * user_vm_start 7f7d26200000 // picked by mmap()
+ * kern_vm_start ffffc90001e69000 // picked by get_vm_area()
+ * For user space all pointers within the arena are normal 8-byte addresses.
+ * In this example 7f7d26200000 is the address of the first page (pgoff=0).
+ * The bpf program will access it as: kern_vm_start + lower_32bit_of_user_ptr
+ * (u32)7f7d26200000 -> 26200000
+ * hence
+ * ffffc90001e69000 + 26200000 == ffffc90028069000 is "pgoff=0" within 4Gb
+ * kernel memory region.
+ *
+ * BPF JITs generate the following code to access arena:
+ * mov eax, eax // eax has lower 32-bit of user pointer
+ * mov word ptr [rax + r12 + off], bx
+ * where r12 == kern_vm_start and off is s16.
+ * Hence allocate 4Gb + GUARD_SZ/2 on each side.
+ *
+ * Initially kernel vm_area and user vma are not populated.
+ * User space can fault-in any address which will insert the page
+ * into kernel and user vma.
+ * bpf program can allocate a page via bpf_arena_alloc_pages() kfunc
+ * which will insert it into kernel vm_area.
+ * The later fault-in from user space will populate that page into user vma.
+ */
+
+/* number of bytes addressable by LDX/STX insn with 16-bit 'off' field */
+#define GUARD_SZ (1ull << sizeof(((struct bpf_insn *)0)->off) * 8)
+#define KERN_VM_SZ ((1ull << 32) + GUARD_SZ)
+
+struct bpf_arena {
+ struct bpf_map map;
+ u64 user_vm_start;
+ u64 user_vm_end;
+ struct vm_struct *kern_vm;
+ struct maple_tree mt;
+ struct list_head vma_list;
+ struct mutex lock;
+};
+
+u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena)
+{
+ return arena ? (u64) (long) arena->kern_vm->addr + GUARD_SZ / 2 : 0;
+}
+
+u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena)
+{
+ return arena ? arena->user_vm_start : 0;
+}
+
+static long arena_map_peek_elem(struct bpf_map *map, void *value)
+{
+ return -EOPNOTSUPP;
+}
+
+static long arena_map_push_elem(struct bpf_map *map, void *value, u64 flags)
+{
+ return -EOPNOTSUPP;
+}
+
+static long arena_map_pop_elem(struct bpf_map *map, void *value)
+{
+ return -EOPNOTSUPP;
+}
+
+static long arena_map_delete_elem(struct bpf_map *map, void *value)
+{
+ return -EOPNOTSUPP;
+}
+
+static int arena_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
+{
+ return -EOPNOTSUPP;
+}
+
+static long compute_pgoff(struct bpf_arena *arena, long uaddr)
+{
+ return (u32)(uaddr - (u32)arena->user_vm_start) >> PAGE_SHIFT;
+}
+
+static struct bpf_map *arena_map_alloc(union bpf_attr *attr)
+{
+ struct vm_struct *kern_vm;
+ int numa_node = bpf_map_attr_numa_node(attr);
+ struct bpf_arena *arena;
+ u64 vm_range;
+ int err = -ENOMEM;
+
+ if (attr->key_size || attr->value_size || attr->max_entries == 0 ||
+ /* BPF_F_MMAPABLE must be set */
+ !(attr->map_flags & BPF_F_MMAPABLE) ||
+ /* No unsupported flags present */
+ (attr->map_flags & ~(BPF_F_SEGV_ON_FAULT | BPF_F_MMAPABLE | BPF_F_NO_USER_CONV)))
+ return ERR_PTR(-EINVAL);
+
+ if (attr->map_extra & ~PAGE_MASK)
+ /* If non-zero the map_extra is an expected user VMA start address */
+ return ERR_PTR(-EINVAL);
+
+ vm_range = (u64)attr->max_entries * PAGE_SIZE;
+ if (vm_range > (1ull << 32))
+ return ERR_PTR(-E2BIG);
+
+ if ((attr->map_extra >> 32) != ((attr->map_extra + vm_range - 1) >> 32))
+ /* user vma must not cross 32-bit boundary */
+ return ERR_PTR(-ERANGE);
+
+ kern_vm = get_vm_area(KERN_VM_SZ, VM_SPARSE | VM_USERMAP);
+ if (!kern_vm)
+ return ERR_PTR(-ENOMEM);
+
+ arena = bpf_map_area_alloc(sizeof(*arena), numa_node);
+ if (!arena)
+ goto err;
+
+ arena->kern_vm = kern_vm;
+ arena->user_vm_start = attr->map_extra;
+ if (arena->user_vm_start)
+ arena->user_vm_end = arena->user_vm_start + vm_range;
+
+ INIT_LIST_HEAD(&arena->vma_list);
+ bpf_map_init_from_attr(&arena->map, attr);
+ mt_init_flags(&arena->mt, MT_FLAGS_ALLOC_RANGE);
+ mutex_init(&arena->lock);
+
+ return &arena->map;
+err:
+ free_vm_area(kern_vm);
+ return ERR_PTR(err);
+}
+
+static int existing_page_cb(pte_t *ptep, unsigned long addr, void *data)
+{
+ struct page *page;
+ pte_t pte;
+
+ pte = ptep_get(ptep);
+ if (!pte_present(pte)) /* sanity check */
+ return 0;
+ page = pte_page(pte);
+ /*
+ * We do not update pte here:
+ * 1. Nobody should be accessing bpf_arena's range outside of a kernel bug
+ * 2. TLB flushing is batched or deferred. Even if we clear pte,
+ * the TLB entries can stick around and continue to permit access to
+ * the freed page. So it all relies on 1.
+ */
+ __free_page(page);
+ return 0;
+}
+
+static void arena_map_free(struct bpf_map *map)
+{
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+ /*
+ * Check that user vma-s are not around when bpf map is freed.
+ * mmap() holds vm_file which holds bpf_map refcnt.
+ * munmap() must have happened on vma followed by arena_vm_close()
+ * which would clear arena->vma_list.
+ */
+ if (WARN_ON_ONCE(!list_empty(&arena->vma_list)))
+ return;
+
+ /*
+ * free_vm_area() calls remove_vm_area() that calls free_unmap_vmap_area().
+ * It unmaps everything from vmalloc area and clears pgtables.
+ * Call apply_to_existing_page_range() first to find populated ptes and
+ * free those pages.
+ */
+ apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena),
+ KERN_VM_SZ - GUARD_SZ, existing_page_cb, NULL);
+ free_vm_area(arena->kern_vm);
+ mtree_destroy(&arena->mt);
+ bpf_map_area_free(arena);
+}
+
+static void *arena_map_lookup_elem(struct bpf_map *map, void *key)
+{
+ return ERR_PTR(-EINVAL);
+}
+
+static long arena_map_update_elem(struct bpf_map *map, void *key,
+ void *value, u64 flags)
+{
+ return -EOPNOTSUPP;
+}
+
+static int arena_map_check_btf(const struct bpf_map *map, const struct btf *btf,
+ const struct btf_type *key_type, const struct btf_type *value_type)
+{
+ return 0;
+}
+
+static u64 arena_map_mem_usage(const struct bpf_map *map)
+{
+ return 0;
+}
+
+struct vma_list {
+ struct vm_area_struct *vma;
+ struct list_head head;
+};
+
+static int remember_vma(struct bpf_arena *arena, struct vm_area_struct *vma)
+{
+ struct vma_list *vml;
+
+ vml = kmalloc(sizeof(*vml), GFP_KERNEL);
+ if (!vml)
+ return -ENOMEM;
+ vma->vm_private_data = vml;
+ vml->vma = vma;
+ list_add(&vml->head, &arena->vma_list);
+ return 0;
+}
+
+static void arena_vm_close(struct vm_area_struct *vma)
+{
+ struct bpf_map *map = vma->vm_file->private_data;
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+ struct vma_list *vml;
+
+ guard(mutex)(&arena->lock);
+ vml = vma->vm_private_data;
+ list_del(&vml->head);
+ vma->vm_private_data = NULL;
+ kfree(vml);
+}
+
+#define MT_ENTRY ((void *)&arena_map_ops) /* unused. has to be valid pointer */
+
+static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
+{
+ struct bpf_map *map = vmf->vma->vm_file->private_data;
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+ struct page *page;
+ long kbase, kaddr;
+ int ret;
+
+ kbase = bpf_arena_get_kern_vm_start(arena);
+ kaddr = kbase + (u32)(vmf->address & PAGE_MASK);
+
+ guard(mutex)(&arena->lock);
+ page = vmalloc_to_page((void *)kaddr);
+ if (page)
+ /* already have a page vmap-ed */
+ goto out;
+
+ if (arena->map.map_flags & BPF_F_SEGV_ON_FAULT)
+ /* User space requested to segfault when page is not allocated by bpf prog */
+ return VM_FAULT_SIGSEGV;
+
+ ret = mtree_insert(&arena->mt, vmf->pgoff, MT_ENTRY, GFP_KERNEL);
+ if (ret)
+ return VM_FAULT_SIGSEGV;
+
+ /* Account into memcg of the process that created bpf_arena */
+ ret = bpf_map_alloc_pages(map, GFP_KERNEL | __GFP_ZERO, NUMA_NO_NODE, 1, &page);
+ if (ret) {
+ mtree_erase(&arena->mt, vmf->pgoff);
+ return VM_FAULT_SIGSEGV;
+ }
+
+ ret = vm_area_map_pages(arena->kern_vm, kaddr, kaddr + PAGE_SIZE, &page);
+ if (ret) {
+ mtree_erase(&arena->mt, vmf->pgoff);
+ __free_page(page);
+ return VM_FAULT_SIGSEGV;
+ }
+out:
+ page_ref_add(page, 1);
+ vmf->page = page;
+ return 0;
+}
+
+static const struct vm_operations_struct arena_vm_ops = {
+ .close = arena_vm_close,
+ .fault = arena_vm_fault,
+};
+
+static unsigned long arena_get_unmapped_area(struct file *filp, unsigned long addr,
+ unsigned long len, unsigned long pgoff,
+ unsigned long flags)
+{
+ struct bpf_map *map = filp->private_data;
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+ long ret;
+
+ if (pgoff)
+ return -EINVAL;
+ if (len > (1ull << 32))
+ return -E2BIG;
+
+ /* if user_vm_start was specified at arena creation time */
+ if (arena->user_vm_start) {
+ if (len > arena->user_vm_end - arena->user_vm_start)
+ return -E2BIG;
+ if (len != arena->user_vm_end - arena->user_vm_start)
+ return -EINVAL;
+ if (addr != arena->user_vm_start)
+ return -EINVAL;
+ }
+
+ ret = current->mm->get_unmapped_area(filp, addr, len * 2, 0, flags);
+ if (IS_ERR_VALUE(ret))
+ return ret;
+ if ((ret >> 32) == ((ret + len - 1) >> 32))
+ return ret;
+ if (WARN_ON_ONCE(arena->user_vm_start))
+ /* checks at map creation time should prevent this */
+ return -EFAULT;
+ return round_up(ret, 1ull << 32);
+}
+
+static int arena_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
+{
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+ guard(mutex)(&arena->lock);
+ if (arena->user_vm_start && arena->user_vm_start != vma->vm_start)
+ /*
+ * If map_extra was not specified at arena creation time then
+ * 1st user process can do mmap(NULL, ...) to pick user_vm_start
+ * 2nd user process must pass the same addr to mmap(addr, MAP_FIXED..);
+ * or
+ * specify addr in map_extra and
+ * use the same addr later with mmap(addr, MAP_FIXED..);
+ */
+ return -EBUSY;
+
+ if (arena->user_vm_end && arena->user_vm_end != vma->vm_end)
+ /* all user processes must have the same size of mmap-ed region */
+ return -EBUSY;
+
+ /* Earlier checks should prevent this */
+ if (WARN_ON_ONCE(vma->vm_end - vma->vm_start > (1ull << 32) || vma->vm_pgoff))
+ return -EFAULT;
+
+ if (remember_vma(arena, vma))
+ return -ENOMEM;
+
+ arena->user_vm_start = vma->vm_start;
+ arena->user_vm_end = vma->vm_end;
+ /*
+ * bpf_map_mmap() checks that it's being mmaped as VM_SHARED and
+ * clears VM_MAYEXEC. Set VM_DONTEXPAND as well to avoid
+ * potential change of user_vm_start.
+ */
+ vm_flags_set(vma, VM_DONTEXPAND);
+ vma->vm_ops = &arena_vm_ops;
+ return 0;
+}
+
+static int arena_map_direct_value_addr(const struct bpf_map *map, u64 *imm, u32 off)
+{
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+ if ((u64)off > arena->user_vm_end - arena->user_vm_start)
+ return -ERANGE;
+ *imm = (unsigned long)arena->user_vm_start;
+ return 0;
+}
+
+BTF_ID_LIST_SINGLE(bpf_arena_map_btf_ids, struct, bpf_arena)
+const struct bpf_map_ops arena_map_ops = {
+ .map_meta_equal = bpf_map_meta_equal,
+ .map_alloc = arena_map_alloc,
+ .map_free = arena_map_free,
+ .map_direct_value_addr = arena_map_direct_value_addr,
+ .map_mmap = arena_map_mmap,
+ .map_get_unmapped_area = arena_get_unmapped_area,
+ .map_get_next_key = arena_map_get_next_key,
+ .map_push_elem = arena_map_push_elem,
+ .map_peek_elem = arena_map_peek_elem,
+ .map_pop_elem = arena_map_pop_elem,
+ .map_lookup_elem = arena_map_lookup_elem,
+ .map_update_elem = arena_map_update_elem,
+ .map_delete_elem = arena_map_delete_elem,
+ .map_check_btf = arena_map_check_btf,
+ .map_mem_usage = arena_map_mem_usage,
+ .map_btf_id = &bpf_arena_map_btf_ids[0],
+};
+
+static u64 clear_lo32(u64 val)
+{
+ return val & ~(u64)~0U;
+}
+
+/*
+ * Allocate pages and vmap them into kernel vmalloc area.
+ * Later the pages will be mmaped into user space vma.
+ */
+static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt, int node_id)
+{
+ /* user_vm_end/start are fixed before bpf prog runs */
+ long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT;
+ u64 kern_vm_start = bpf_arena_get_kern_vm_start(arena);
+ struct page **pages;
+ long pgoff = 0;
+ u32 uaddr32;
+ int ret, i;
+
+ if (page_cnt > page_cnt_max)
+ return 0;
+
+ if (uaddr) {
+ if (uaddr & ~PAGE_MASK)
+ return 0;
+ pgoff = compute_pgoff(arena, uaddr);
+ if (pgoff + page_cnt > page_cnt_max)
+ /* requested address will be outside of user VMA */
+ return 0;
+ }
+
+ /* zeroing is needed, since alloc_pages_bulk_array() only fills in non-zero entries */
+ pages = kvcalloc(page_cnt, sizeof(struct page *), GFP_KERNEL);
+ if (!pages)
+ return 0;
+
+ guard(mutex)(&arena->lock);
+
+ if (uaddr)
+ ret = mtree_insert_range(&arena->mt, pgoff, pgoff + page_cnt - 1,
+ MT_ENTRY, GFP_KERNEL);
+ else
+ ret = mtree_alloc_range(&arena->mt, &pgoff, MT_ENTRY,
+ page_cnt, 0, page_cnt_max - 1, GFP_KERNEL);
+ if (ret)
+ goto out_free_pages;
+
+ ret = bpf_map_alloc_pages(&arena->map, GFP_KERNEL | __GFP_ZERO,
+ node_id, page_cnt, pages);
+ if (ret)
+ goto out;
+
+ uaddr32 = (u32)(arena->user_vm_start + pgoff * PAGE_SIZE);
+ /* Earlier checks make sure that uaddr32 + page_cnt * PAGE_SIZE will not overflow 32-bit */
+ ret = vm_area_map_pages(arena->kern_vm, kern_vm_start + uaddr32,
+ kern_vm_start + uaddr32 + page_cnt * PAGE_SIZE, pages);
+ if (ret) {
+ for (i = 0; i < page_cnt; i++)
+ __free_page(pages[i]);
+ goto out;
+ }
+ kvfree(pages);
+ return clear_lo32(arena->user_vm_start) + uaddr32;
+out:
+ mtree_erase(&arena->mt, pgoff);
+out_free_pages:
+ kvfree(pages);
+ return 0;
+}
+
+/*
+ * If page is present in vmalloc area, unmap it from vmalloc area,
+ * unmap it from all user space vma-s,
+ * and free it.
+ */
+static void zap_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
+{
+ struct vma_list *vml;
+
+ list_for_each_entry(vml, &arena->vma_list, head)
+ zap_page_range_single(vml->vma, uaddr,
+ PAGE_SIZE * page_cnt, NULL);
+}
+
+static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
+{
+ u64 full_uaddr, uaddr_end;
+ long kaddr, pgoff, i;
+ struct page *page;
+
+ /* only aligned lower 32-bit are relevant */
+ uaddr = (u32)uaddr;
+ uaddr &= PAGE_MASK;
+ full_uaddr = clear_lo32(arena->user_vm_start) + uaddr;
+ uaddr_end = min(arena->user_vm_end, full_uaddr + (page_cnt << PAGE_SHIFT));
+ if (full_uaddr >= uaddr_end)
+ return;
+
+ page_cnt = (uaddr_end - full_uaddr) >> PAGE_SHIFT;
+
+ guard(mutex)(&arena->lock);
+
+ pgoff = compute_pgoff(arena, uaddr);
+ /* clear range */
+ mtree_store_range(&arena->mt, pgoff, pgoff + page_cnt - 1, NULL, GFP_KERNEL);
+
+ if (page_cnt > 1)
+ /* bulk zap if multiple pages being freed */
+ zap_pages(arena, full_uaddr, page_cnt);
+
+ kaddr = bpf_arena_get_kern_vm_start(arena) + uaddr;
+ for (i = 0; i < page_cnt; i++, kaddr += PAGE_SIZE, full_uaddr += PAGE_SIZE) {
+ page = vmalloc_to_page((void *)kaddr);
+ if (!page)
+ continue;
+ if (page_cnt == 1 && page_mapped(page)) /* mapped by some user process */
+ zap_pages(arena, full_uaddr, 1);
+ vm_area_unmap_pages(arena->kern_vm, kaddr, kaddr + PAGE_SIZE);
+ __free_page(page);
+ }
+}
+
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc void *bpf_arena_alloc_pages(void *p__map, void *addr__ign, u32 page_cnt,
+ int node_id, u64 flags)
+{
+ struct bpf_map *map = p__map;
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+ if (map->map_type != BPF_MAP_TYPE_ARENA || flags || !page_cnt)
+ return NULL;
+
+ return (void *)arena_alloc_pages(arena, (long)addr__ign, page_cnt, node_id);
+}
+
+__bpf_kfunc void bpf_arena_free_pages(void *p__map, void *ptr__ign, u32 page_cnt)
+{
+ struct bpf_map *map = p__map;
+ struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+ if (map->map_type != BPF_MAP_TYPE_ARENA || !page_cnt || !ptr__ign)
+ return;
+ arena_free_pages(arena, (long)ptr__ign, page_cnt);
+}
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(arena_kfuncs)
+BTF_ID_FLAGS(func, bpf_arena_alloc_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_arena_free_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE)
+BTF_KFUNCS_END(arena_kfuncs)
+
+static const struct btf_kfunc_id_set common_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &arena_kfuncs,
+};
+
+static int __init kfunc_init(void)
+{
+ return register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &common_kfunc_set);
+}
+late_initcall(kfunc_init);
projects / mirror_ubuntu-kernels.git / commitdiff