Commit 3ca1032a authored by KP Singh's avatar KP Singh Committed by Alexei Starovoitov
Browse files

bpf: Implement get_current_task_btf and RET_PTR_TO_BTF_ID 



The currently available bpf_get_current_task returns an unsigned integer
which can be used along with BPF_CORE_READ to read data from
the task_struct but still cannot be used as an input argument to a
helper that accepts an ARG_PTR_TO_BTF_ID of type task_struct.

In order to implement this helper a new return type, RET_PTR_TO_BTF_ID,
is added. This is similar to RET_PTR_TO_BTF_ID_OR_NULL but does not
require checking the nullness of returned pointer.

Signed-off-by: default avatarKP Singh <kpsingh@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201106103747.2780972-6-kpsingh@chromium.org
parent 864ab061

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -310,6 +310,7 @@ enum bpf_return_type { 
	RET_PTR_TO_BTF_ID_OR_NULL,	/* returns a pointer to a btf_id or NULL */

	RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, /* returns a pointer to a valid memory or a btf_id or NULL */

	RET_PTR_TO_MEM_OR_BTF_ID,	/* returns a pointer to a valid memory or a btf_id */

	RET_PTR_TO_BTF_ID,		/* returns a pointer to a btf_id */

};



/* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs

include/uapi/linux/bpf.h

+9 −0
Original line number Diff line number Diff line
@@ -3779,6 +3779,14 @@ union bpf_attr { 
 *		0 on success.

 *

 *		**-ENOENT** if the bpf_local_storage cannot be found.

 *

 * struct task_struct *bpf_get_current_task_btf(void)

 *	Description

 *		Return a BTF pointer to the "current" task.

 *		This pointer can also be used in helpers that accept an

 *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.

 *	Return

 *		Pointer to the current task.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -3939,6 +3947,7 @@ union bpf_attr { 
	FN(redirect_peer),		\

	FN(task_storage_get),		\

	FN(task_storage_delete),	\

	FN(get_current_task_btf),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

kernel/bpf/verifier.c

+5 −2
Original line number Diff line number Diff line
@@ -5186,11 +5186,14 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn 
				PTR_TO_BTF_ID : PTR_TO_BTF_ID_OR_NULL;

			regs[BPF_REG_0].btf_id = meta.ret_btf_id;

		}

	} else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {

	} else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL ||

		   fn->ret_type == RET_PTR_TO_BTF_ID) {

		int ret_btf_id;



		mark_reg_known_zero(env, regs, BPF_REG_0);

		regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;

		regs[BPF_REG_0].type = fn->ret_type == RET_PTR_TO_BTF_ID ?

						     PTR_TO_BTF_ID :

						     PTR_TO_BTF_ID_OR_NULL;

		ret_btf_id = *fn->ret_btf_id;

		if (ret_btf_id == 0) {

			verbose(env, "invalid return type %d of func %s#%d\n",

kernel/trace/bpf_trace.c

+16 −0
Original line number Diff line number Diff line
@@ -1022,6 +1022,20 @@ const struct bpf_func_proto bpf_get_current_task_proto = { 
	.ret_type	= RET_INTEGER,

};



BPF_CALL_0(bpf_get_current_task_btf)

{

	return (unsigned long) current;

}



BTF_ID_LIST_SINGLE(bpf_get_current_btf_ids, struct, task_struct)



static const struct bpf_func_proto bpf_get_current_task_btf_proto = {

	.func		= bpf_get_current_task_btf,

	.gpl_only	= true,

	.ret_type	= RET_PTR_TO_BTF_ID,

	.ret_btf_id	= &bpf_get_current_btf_ids[0],

};



BPF_CALL_2(bpf_current_task_under_cgroup, struct bpf_map *, map, u32, idx)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);
@@ -1265,6 +1279,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_get_current_pid_tgid_proto;

	case BPF_FUNC_get_current_task:

		return &bpf_get_current_task_proto;

	case BPF_FUNC_get_current_task_btf:

		return &bpf_get_current_task_btf_proto;

	case BPF_FUNC_get_current_uid_gid:

		return &bpf_get_current_uid_gid_proto;

	case BPF_FUNC_get_current_comm:

tools/include/uapi/linux/bpf.h

+9 −0
Original line number Diff line number Diff line
@@ -3779,6 +3779,14 @@ union bpf_attr { 
 *		0 on success.

 *

 *		**-ENOENT** if the bpf_local_storage cannot be found.

 *

 * struct task_struct *bpf_get_current_task_btf(void)

 *	Description

 *		Return a BTF pointer to the "current" task.

 *		This pointer can also be used in helpers that accept an

 *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.

 *	Return

 *		Pointer to the current task.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -3939,6 +3947,7 @@ union bpf_attr { 
	FN(redirect_peer),		\

	FN(task_storage_get),		\

	FN(task_storage_delete),	\

	FN(get_current_task_btf),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper