get_stack_offset.bpf.c

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2021 Yonatan Goldschmidt
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <linux/bpf.h>
#include <linux/types.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_core_read.h>

#include "get_stack_offset.h"

// key - zero
// value - struct output
struct {
    __uint(type, BPF_MAP_TYPE_HASH);
    __uint(max_entries, 1);
    __type(key, __u32);
    __type(value, struct output);
} output SEC(".maps");

// see https://nakryiko.com/posts/bpf-core-reference-guide/#defining-own-co-re-relocatable-type-definitions
struct task_struct {
	void *stack;
} __attribute__((preserve_access_index));


SEC("tp/syscalls/sys_enter_write")
int do_write(struct pt_regs *ctx)
{
    struct output out;
    const __u32 zero = 0;
    out.offset = 0;
    out.status = STATUS_ERROR;

    out.offset = bpf_core_field_offset(struct task_struct, stack);
    if (out.offset >= 0 )
        out.status = STATUS_OK;
    bpf_map_update_elem(&output, &zero, &out, BPF_ANY);

    return 0;
}

char LICENSE[] SEC("license") = "Dual MIT/GPL";