Commit 27ae7997 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS 



This patch allows the kernel's struct ops (i.e. func ptr) to be
implemented in BPF.  The first use case in this series is the
"struct tcp_congestion_ops" which will be introduced in a
latter patch.

This patch introduces a new prog type BPF_PROG_TYPE_STRUCT_OPS.
The BPF_PROG_TYPE_STRUCT_OPS prog is verified against a particular
func ptr of a kernel struct.  The attr->attach_btf_id is the btf id
of a kernel struct.  The attr->expected_attach_type is the member
"index" of that kernel struct.  The first member of a struct starts
with member index 0.  That will avoid ambiguity when a kernel struct
has multiple func ptrs with the same func signature.

For example, a BPF_PROG_TYPE_STRUCT_OPS prog is written
to implement the "init" func ptr of the "struct tcp_congestion_ops".
The attr->attach_btf_id is the btf id of the "struct tcp_congestion_ops"
of the _running_ kernel.  The attr->expected_attach_type is 3.

The ctx of BPF_PROG_TYPE_STRUCT_OPS is an array of u64 args saved
by arch_prepare_bpf_trampoline that will be done in the next
patch when introducing BPF_MAP_TYPE_STRUCT_OPS.

"struct bpf_struct_ops" is introduced as a common interface for the kernel
struct that supports BPF_PROG_TYPE_STRUCT_OPS prog.  The supporting kernel
struct will need to implement an instance of the "struct bpf_struct_ops".

The supporting kernel struct also needs to implement a bpf_verifier_ops.
During BPF_PROG_LOAD, bpf_struct_ops_find() will find the right
bpf_verifier_ops by searching the attr->attach_btf_id.

A new "btf_struct_access" is also added to the bpf_verifier_ops such
that the supporting kernel struct can optionally provide its own specific
check on accessing the func arg (e.g. provide limited write access).

After btf_vmlinux is parsed, the new bpf_struct_ops_init() is called
to initialize some values (e.g. the btf id of the supporting kernel
struct) and it can only be done once the btf_vmlinux is available.

The R0 checks at BPF_EXIT is excluded for the BPF_PROG_TYPE_STRUCT_OPS prog
if the return type of the prog->aux->attach_func_proto is "void".

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200109003503.3855825-1-kafai@fb.com
parent 976aba00

include/linux/bpf.h

+30 −0
Original line number Diff line number Diff line
@@ -349,6 +349,10 @@ struct bpf_verifier_ops { 
				  const struct bpf_insn *src,

				  struct bpf_insn *dst,

				  struct bpf_prog *prog, u32 *target_size);

	int (*btf_struct_access)(struct bpf_verifier_log *log,

				 const struct btf_type *t, int off, int size,

				 enum bpf_access_type atype,

				 u32 *next_btf_id);

};



struct bpf_prog_offload_ops {
@@ -668,6 +672,32 @@ struct bpf_array_aux { 
	struct work_struct work;

};



struct btf_type;

struct btf_member;



#define BPF_STRUCT_OPS_MAX_NR_MEMBERS 64

struct bpf_struct_ops {

	const struct bpf_verifier_ops *verifier_ops;

	int (*init)(struct btf *btf);

	int (*check_member)(const struct btf_type *t,

			    const struct btf_member *member);

	const struct btf_type *type;

	const char *name;

	struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS];

	u32 type_id;

};



#if defined(CONFIG_BPF_JIT) && defined(CONFIG_BPF_SYSCALL)

const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id);

void bpf_struct_ops_init(struct btf *btf);

#else

static inline const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)

{

	return NULL;

}

static inline void bpf_struct_ops_init(struct btf *btf) { }

#endif



struct bpf_array {

	struct bpf_map map;

	u32 elem_size;

include/linux/bpf_types.h

+4 −0
Original line number Diff line number Diff line
@@ -65,6 +65,10 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_LIRC_MODE2, lirc_mode2, 
BPF_PROG_TYPE(BPF_PROG_TYPE_SK_REUSEPORT, sk_reuseport,

	      struct sk_reuseport_md, struct sk_reuseport_kern)

#endif

#if defined(CONFIG_BPF_JIT)

BPF_PROG_TYPE(BPF_PROG_TYPE_STRUCT_OPS, bpf_struct_ops,

	      void *, void *)

#endif



BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)

BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)

include/linux/btf.h

+34 −0
Original line number Diff line number Diff line
@@ -53,6 +53,18 @@ bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s, 
			   u32 expected_offset, u32 expected_size);

int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t);

bool btf_type_is_void(const struct btf_type *t);

s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind);

const struct btf_type *btf_type_skip_modifiers(const struct btf *btf,

					       u32 id, u32 *res_id);

const struct btf_type *btf_type_resolve_ptr(const struct btf *btf,

					    u32 id, u32 *res_id);

const struct btf_type *btf_type_resolve_func_ptr(const struct btf *btf,

						 u32 id, u32 *res_id);



#define for_each_member(i, struct_type, member)			\

	for (i = 0, member = btf_type_member(struct_type);	\

	     i < btf_type_vlen(struct_type);			\

	     i++, member++)



static inline bool btf_type_is_ptr(const struct btf_type *t)

{
@@ -84,6 +96,28 @@ static inline bool btf_type_is_func_proto(const struct btf_type *t) 
	return BTF_INFO_KIND(t->info) == BTF_KIND_FUNC_PROTO;

}



static inline u16 btf_type_vlen(const struct btf_type *t)

{

	return BTF_INFO_VLEN(t->info);

}



static inline bool btf_type_kflag(const struct btf_type *t)

{

	return BTF_INFO_KFLAG(t->info);

}



static inline u32 btf_member_bitfield_size(const struct btf_type *struct_type,

					   const struct btf_member *member)

{

	return btf_type_kflag(struct_type) ? BTF_MEMBER_BITFIELD_SIZE(member->offset)

					   : 0;

}



static inline const struct btf_member *btf_type_member(const struct btf_type *t)

{

	return (const struct btf_member *)(t + 1);

}



#ifdef CONFIG_BPF_SYSCALL

const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);

const char *btf_name_by_offset(const struct btf *btf, u32 offset);

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -174,6 +174,7 @@ enum bpf_prog_type { 
	BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,

	BPF_PROG_TYPE_CGROUP_SOCKOPT,

	BPF_PROG_TYPE_TRACING,

	BPF_PROG_TYPE_STRUCT_OPS,

};



enum bpf_attach_type {

kernel/bpf/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -27,3 +27,6 @@ endif 
ifeq ($(CONFIG_SYSFS),y)

obj-$(CONFIG_DEBUG_INFO_BTF) += sysfs_btf.o

endif

ifeq ($(CONFIG_BPF_JIT),y)

obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o

endif

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