path: root/tools/lib/bpf/gen_loader.c

// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2021 Facebook */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <linux/filter.h>
#include <sys/param.h>
#include "btf.h"
#include "bpf.h"
#include "libbpf.h"
#include "libbpf_internal.h"
#include "hashmap.h"
#include "bpf_gen_internal.h"
#include "skel_internal.h"
#include <asm/byteorder.h>

#define MAX_USED_MAPS	64
#define MAX_USED_PROGS	32
#define MAX_KFUNC_DESCS 256
#define MAX_FD_ARRAY_SZ (MAX_USED_MAPS + MAX_KFUNC_DESCS)

/* The following structure describes the stack layout of the loader program.
 * In addition R6 contains the pointer to context.
 * R7 contains the result of the last sys_bpf command (typically error or FD).
 * R9 contains the result of the last sys_close command.
 *
 * Naming convention:
 * ctx - bpf program context
 * stack - bpf program stack
 * blob - bpf_attr-s, strings, insns, map data.
 *        All the bytes that loader prog will use for read/write.
 */
struct loader_stack {
	__u32 btf_fd;
	__u32 inner_map_fd;
	__u32 prog_fd[MAX_USED_PROGS];
};

#define stack_off(field) \
	(__s16)(-sizeof(struct loader_stack) + offsetof(struct loader_stack, field))

#define attr_field(attr, field) (attr + offsetof(union bpf_attr, field))

static int blob_fd_array_off(struct bpf_gen *gen, int index)
{
	return gen->fd_array + index * sizeof(int);
}

static int realloc_insn_buf(struct bpf_gen *gen, __u32 size)
{
	size_t off = gen->insn_cur - gen->insn_start;
	void *insn_start;

	if (gen->error)
		return gen->error;
	if (size > INT32_MAX || off + size > INT32_MAX) {
		gen->error = -ERANGE;
		return -ERANGE;
	}
	insn_start = realloc(gen->insn_start, off + size);
	if (!insn_start) {
		gen->error = -ENOMEM;
		free(gen->insn_start);
		gen->insn_start = NULL;
		return -ENOMEM;
	}
	gen->insn_start = insn_start;
	gen->insn_cur = insn_start + off;
	return 0;
}

static int realloc_data_buf(struct bpf_gen *gen, __u32 size)
{
	size_t off = gen->data_cur - gen->data_start;
	void *data_start;

	if (gen->error)
		return gen->error;
	if (size > INT32_MAX || off + size > INT32_MAX) {
		gen->error = -ERANGE;
		return -ERANGE;
	}
	data_start = realloc(gen->data_start, off + size);
	if (!data_start) {
		gen->error = -ENOMEM;
		free(gen->data_start);
		gen->data_start = NULL;
		return -ENOMEM;
	}
	gen->data_start = data_start;
	gen->data_cur = data_start + off;
	return 0;
}

static void emit(struct bpf_gen *gen, struct bpf_insn insn)
{
	if (realloc_insn_buf(gen, sizeof(insn)))
		return;
	memcpy(gen->insn_cur, &insn, sizeof(insn));
	gen->insn_cur += sizeof(insn);
}

static void emit2(struct bpf_gen *gen, struct bpf_insn insn1, struct bpf_insn insn2)
{
	emit(gen, insn1);
	emit(gen, insn2);
}

static int add_data(struct bpf_gen *gen, const void *data, __u32 size);
static void emit_sys_close_blob(struct bpf_gen *gen, int blob_off);

void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps)
{
	size_t stack_sz = sizeof(struct loader_stack), nr_progs_sz;
	int i;

	gen->fd_array = add_data(gen, NULL, MAX_FD_ARRAY_SZ * sizeof(int));
	gen->log_level = log_level;
	/* save ctx pointer into R6 */
	emit(gen, BPF_MOV64_REG(BPF_REG_6, BPF_REG_1));

	/* bzero stack */
	emit(gen, BPF_MOV64_REG(BPF_REG_1, BPF_REG_10));
	emit(gen, BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -stack_sz));
	emit(gen, BPF_MOV64_IMM(BPF_REG_2, stack_sz));
	emit(gen, BPF_MOV64_IMM(BPF_REG_3, 0));
	emit(gen, BPF_EMIT_CALL(BPF_FUNC_probe_read_kernel));

	/* amount of stack actually used, only used to calculate iterations, not stack offset */
	nr_progs_sz = offsetof(struct loader_stack, prog_fd[nr_progs]);
	/* jump over cleanup code */
	emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0,
			      /* size of cleanup code below (including map fd cleanup) */
			      (nr_progs_sz / 4) * 3 + 2 +
			      /* 6 insns for emit_sys_close_blob,