// SPDX-License-Identifier: GPL-2.0
/*
 * Seccomp BPF helper functions
 *
 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
 * Author: Will Drewry <wad@chromium.org>
 *
 * The code may be used by anyone for any purpose,
 * and can serve as a starting point for developing
 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "bpf-helper.h"

int bpf_resolve_jumps(struct bpf_labels *labels,
                      struct sock_filter *filter, size_t count)
{
        size_t i;

        if (count < 1 || count > BPF_MAXINSNS)
                return -1;
        /*
        * Walk it once, backwards, to build the label table and do fixups.
        * Since backward jumps are disallowed by BPF, this is easy.
        */
        for (i = 0; i < count; ++i) {
                size_t offset = count - i - 1;
                struct sock_filter *instr = &filter[offset];
                if (instr->code != (BPF_JMP+BPF_JA))
                        continue;
                switch ((instr->jt<<8)|instr->jf) {
                case (JUMP_JT<<8)|JUMP_JF:
                        if (labels->labels[instr->k].location == 0xffffffff) {
                                fprintf(stderr, "Unresolved label: '%s'\n",
                                        labels->labels[instr->k].label);
                                return 1;
                        }
                        instr->k = labels->labels[instr->k].location -
                                    (offset + 1);
                        instr->jt = 0;
                        instr->jf = 0;
                        continue;
                case (LABEL_JT<<8)|LABEL_JF:
                        if (labels->labels[instr->k].location != 0xffffffff) {
                                fprintf(stderr, "Duplicate label use: '%s'\n",
                                        labels->labels[instr->k].label);
                                return 1;
                        }
                        labels->labels[instr->k].location = offset;
                        instr->k = 0; /* fall through */
                        instr->jt = 0;
                        instr->jf = 0;
                        continue;
                }
        }
        return 0;
}

/* Simple lookup table for labels. */
__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
{
        struct __bpf_label *begin = labels->labels, *end;
        int id;

        if (labels->count == BPF_LABELS_MAX) {
                fprintf(stderr, "Too many labels\n");
                exit(1);
        }
        if (labels->count == 0) {
                begin->label = label;
                begin->location = 0xffffffff;
                labels->count++;
                return 0;
        }
        end = begin + labels->count;
        for (id = 0; begin < end; ++begin, ++id) {
                if (!strcmp(label, begin->label))
                        return id;
        }
        begin->label = label;
        begin->location = 0xffffffff;
        labels->count++;
        return id;
}

void seccomp_bpf_print(struct sock_filter *filter, size_t count)
{
        struct sock_filter *end = filter + count;
        for ( ; filter < end; ++filter)
                printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
                        filter->code, filter->jt, filter->jf, filter->k);
}