Commit 0a542a86 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: handle pseudo BPF_CALL insn 



in native eBPF programs userspace is using pseudo BPF_CALL instructions
which encode one of 'enum bpf_func_id' inside insn->imm field.
Verifier checks that program using correct function arguments to given func_id.
If all checks passed, kernel needs to fixup BPF_CALL->imm fields by
replacing func_id with in-kernel function pointer.
eBPF interpreter just calls the function.

In-kernel eBPF users continue to use generic BPF_CALL.

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 09756af4

kernel/bpf/syscall.c

+37 −0
Original line number Diff line number Diff line
@@ -357,6 +357,40 @@ void bpf_register_prog_type(struct bpf_prog_type_list *tl) 
	list_add(&tl->list_node, &bpf_prog_types);

}



/* fixup insn->imm field of bpf_call instructions:

 * if (insn->imm == BPF_FUNC_map_lookup_elem)

 *      insn->imm = bpf_map_lookup_elem - __bpf_call_base;

 * else if (insn->imm == BPF_FUNC_map_update_elem)

 *      insn->imm = bpf_map_update_elem - __bpf_call_base;

 * else ...

 *

 * this function is called after eBPF program passed verification

 */

static void fixup_bpf_calls(struct bpf_prog *prog)

{

	const struct bpf_func_proto *fn;

	int i;



	for (i = 0; i < prog->len; i++) {

		struct bpf_insn *insn = &prog->insnsi[i];



		if (insn->code == (BPF_JMP | BPF_CALL)) {

			/* we reach here when program has bpf_call instructions

			 * and it passed bpf_check(), means that

			 * ops->get_func_proto must have been supplied, check it

			 */

			BUG_ON(!prog->aux->ops->get_func_proto);



			fn = prog->aux->ops->get_func_proto(insn->imm);

			/* all functions that have prototype and verifier allowed

			 * programs to call them, must be real in-kernel functions

			 */

			BUG_ON(!fn->func);

			insn->imm = fn->func - __bpf_call_base;

		}

	}

}



/* drop refcnt on maps used by eBPF program and free auxilary data */

static void free_used_maps(struct bpf_prog_aux *aux)

{
@@ -478,6 +512,9 @@ static int bpf_prog_load(union bpf_attr *attr) 
	if (err < 0)

		goto free_used_maps;



	/* fixup BPF_CALL->imm field */

	fixup_bpf_calls(prog);



	/* eBPF program is ready to be JITed */

	bpf_prog_select_runtime(prog);

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