linux/kernel/bpf/arena.c
Alexei Starovoitov ee498a38f3 bpf: Clarify bpf_arena comments.
Clarify two bpf_arena comments, use existing SZ_4G #define,
improve page_cnt check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20240315021834.62988-2-alexei.starovoitov@gmail.com
2024-03-15 14:23:45 -07:00

570 lines
16 KiB
C

// 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 (SZ_4G + 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 > SZ_4G)
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 > SZ_4G)
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, SZ_4G);
}
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 > SZ_4G || 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_max - page_cnt)
/* 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 made sure that uaddr32 + page_cnt * PAGE_SIZE - 1
* will not overflow 32-bit. Lower 32-bit need to represent
* contiguous user address range.
* Map these pages at kern_vm_start base.
* kern_vm_start + uaddr32 + page_cnt * PAGE_SIZE - 1 can overflow
* lower 32-bit and it's ok.
*/
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 */
/* Optimization for the common case of page_cnt==1:
* If page wasn't mapped into some user vma there
* is no need to call zap_pages which is slow. When
* page_cnt is big it's faster to do the batched zap.
*/
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);