From d83525ca62cf8ebe3271d14c36fb900c294274a2 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 31 Jan 2019 15:40:04 -0800 Subject: bpf: introduce bpf_spin_lock Introduce 'struct bpf_spin_lock' and bpf_spin_lock/unlock() helpers to let bpf program serialize access to other variables. Example: struct hash_elem { int cnt; struct bpf_spin_lock lock; }; struct hash_elem * val = bpf_map_lookup_elem(&hash_map, &key); if (val) { bpf_spin_lock(&val->lock); val->cnt++; bpf_spin_unlock(&val->lock); } Restrictions and safety checks: - bpf_spin_lock is only allowed inside HASH and ARRAY maps. - BTF description of the map is mandatory for safety analysis. - bpf program can take one bpf_spin_lock at a time, since two or more can cause dead locks. - only one 'struct bpf_spin_lock' is allowed per map element. It drastically simplifies implementation yet allows bpf program to use any number of bpf_spin_locks. - when bpf_spin_lock is taken the calls (either bpf2bpf or helpers) are not allowed. - bpf program must bpf_spin_unlock() before return. - bpf program can access 'struct bpf_spin_lock' only via bpf_spin_lock()/bpf_spin_unlock() helpers. - load/store into 'struct bpf_spin_lock lock;' field is not allowed. - to use bpf_spin_lock() helper the BTF description of map value must be a struct and have 'struct bpf_spin_lock anyname;' field at the top level. Nested lock inside another struct is not allowed. - syscall map_lookup doesn't copy bpf_spin_lock field to user space. - syscall map_update and program map_update do not update bpf_spin_lock field. - bpf_spin_lock cannot be on the stack or inside networking packet. bpf_spin_lock can only be inside HASH or ARRAY map value. - bpf_spin_lock is available to root only and to all program types. - bpf_spin_lock is not allowed in inner maps of map-in-map. - ld_abs is not allowed inside spin_lock-ed region. - tracing progs and socket filter progs cannot use bpf_spin_lock due to insufficient preemption checks Implementation details: - cgroup-bpf class of programs can nest with xdp/tc programs. Hence bpf_spin_lock is equivalent to spin_lock_irqsave. Other solutions to avoid nested bpf_spin_lock are possible. Like making sure that all networking progs run with softirq disabled. spin_lock_irqsave is the simplest and doesn't add overhead to the programs that don't use it. - arch_spinlock_t is used when its implemented as queued_spin_lock - archs can force their own arch_spinlock_t - on architectures where queued_spin_lock is not available and sizeof(arch_spinlock_t) != sizeof(__u32) trivial lock is used. - presence of bpf_spin_lock inside map value could have been indicated via extra flag during map_create, but specifying it via BTF is cleaner. It provides introspection for map key/value and reduces user mistakes. Next steps: - allow bpf_spin_lock in other map types (like cgroup local storage) - introduce BPF_F_LOCK flag for bpf_map_update() syscall and helper to request kernel to grab bpf_spin_lock before rewriting the value. That will serialize access to map elements. Acked-by: Peter Zijlstra (Intel) Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- include/linux/bpf.h | 37 ++++++++++++++++++++++++++++++++++--- 1 file changed, 34 insertions(+), 3 deletions(-) (limited to 'include/linux/bpf.h') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 0394f1f9213b..2ae615b48bb8 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -72,14 +72,15 @@ struct bpf_map { u32 value_size; u32 max_entries; u32 map_flags; - u32 pages; + int spin_lock_off; /* >=0 valid offset, <0 error */ u32 id; int numa_node; u32 btf_key_type_id; u32 btf_value_type_id; struct btf *btf; + u32 pages; bool unpriv_array; - /* 55 bytes hole */ + /* 51 bytes hole */ /* The 3rd and 4th cacheline with misc members to avoid false sharing * particularly with refcounting. @@ -91,6 +92,34 @@ struct bpf_map { char name[BPF_OBJ_NAME_LEN]; }; +static inline bool map_value_has_spin_lock(const struct bpf_map *map) +{ + return map->spin_lock_off >= 0; +} + +static inline void check_and_init_map_lock(struct bpf_map *map, void *dst) +{ + if (likely(!map_value_has_spin_lock(map))) + return; + *(struct bpf_spin_lock *)(dst + map->spin_lock_off) = + (struct bpf_spin_lock){}; +} + +/* copy everything but bpf_spin_lock */ +static inline void copy_map_value(struct bpf_map *map, void *dst, void *src) +{ + if (unlikely(map_value_has_spin_lock(map))) { + u32 off = map->spin_lock_off; + + memcpy(dst, src, off); + memcpy(dst + off + sizeof(struct bpf_spin_lock), + src + off + sizeof(struct bpf_spin_lock), + map->value_size - off - sizeof(struct bpf_spin_lock)); + } else { + memcpy(dst, src, map->value_size); + } +} + struct bpf_offload_dev; struct bpf_offloaded_map; @@ -162,6 +191,7 @@ enum bpf_arg_type { ARG_PTR_TO_CTX, /* pointer to context */ ARG_ANYTHING, /* any (initialized) argument is ok */ ARG_PTR_TO_SOCKET, /* pointer to bpf_sock */ + ARG_PTR_TO_SPIN_LOCK, /* pointer to bpf_spin_lock */ }; /* type of values returned from helper functions */ @@ -879,7 +909,8 @@ extern const struct bpf_func_proto bpf_msg_redirect_hash_proto; extern const struct bpf_func_proto bpf_msg_redirect_map_proto; extern const struct bpf_func_proto bpf_sk_redirect_hash_proto; extern const struct bpf_func_proto bpf_sk_redirect_map_proto; - +extern const struct bpf_func_proto bpf_spin_lock_proto; +extern const struct bpf_func_proto bpf_spin_unlock_proto; extern const struct bpf_func_proto bpf_get_local_storage_proto; /* Shared helpers among cBPF and eBPF. */ -- cgit v1.2.3