GPL/Events/Helpers.h

// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause

/*
 * Copyright (C) 2021 Elasticsearch BV
 *
 * This software is dual-licensed under the BSD 2-Clause and GPL v2 licenses.
 * You may choose either one of them if you use this software.
 */

/*      $OpenBSD: strncmp.c,v 1.11 2014/06/10 04:16:57 deraadt Exp $    */

/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef EBPF_EVENTPROBE_HELPERS_H
#define EBPF_EVENTPROBE_HELPERS_H

#include "EbpfEventProto.h"

const volatile int consumer_pid = 0;

#define MEMFD_STRING "memfd:"
#define TMPFS_STRING "tmpfs"
#define DEVSHM_STRING "/dev/shm"

#if BPF_DEBUG_TRACE == 0
#undef bpf_printk
#define bpf_printk(fmt, ...)
#endif

// Compiler barrier, used to prevent compile-time insns reordering and optimizations.
#define barrier() asm volatile("" ::: "memory")

#define DECL_FUNC_ARG(func, arg) const volatile int arg__##func##__##arg##__ = 0;
#define FUNC_ARG_READ(type, func, arg)                                                             \
    ({                                                                                             \
        type _ret;                                                                                 \
        bpf_core_read(&_ret, sizeof(_ret), ctx + arg__##func##__##arg##__);                        \
        _ret;                                                                                      \
    })

/*
 *  Reads the specified argument from struct pt_regs without dereferencing it. Note that
 *  we first have to read the value in struct pt_regs into a volatile temporary (_dst).
 *  Without this, LLVM can generate code like the following, which will fail to verify:
 *
 *  r3 = 8                      # The register value we want to read is at offset 8 in the context
 *  r2 = r1                     # r1 = ctx pointer
 *  r2 += r3                    # Increment ctx ptr to register value we're interested in
 *  r3 = *(u64 *)(r2 +0)        # Dereference it (fail)
 *  dereference of modified ctx ptr R2 off=8 disallowed
 *
 *  The verifier disallows dereferencing the context pointer when it's been
 *  modified. This will often happen as an inlining optimization if dst is
 *  immediately passed into a function. We instead want code like the following
 *  to be generated:
 *
 *  r2 = r1                     # r1 = ctx pointer
 *  r3 = *(u64 *)(r2 + 8)       # Dereference it, putting the increment in the dereference insn
 *  ...pass r3 to a function
 */
#define FUNC_ARG_READ_PTREGS(dst, func, arg)                                                       \
    ({                                                                                             \
        int ret = 0;                                                                               \
        volatile typeof(dst) _dst;                                                                 \
        switch (arg__##func##__##arg##__) {                                                        \
        case 0:                                                                                    \
            _dst = (typeof(dst))PT_REGS_PARM1(ctx);                                                \
            break;                                                                                 \
        case 1:                                                                                    \
            _dst = (typeof(dst))PT_REGS_PARM2(ctx);                                                \
            break;                                                                                 \
        case 2:                                                                                    \
            _dst = (typeof(dst))PT_REGS_PARM3(ctx);                                                \
            break;                                                                                 \
        case 3:                                                                                    \
            _dst = (typeof(dst))PT_REGS_PARM4(ctx);                                                \
            break;                                                                                 \
        case 4:                                                                                    \
            _dst = (typeof(dst))PT_REGS_PARM5(ctx);                                                \
            break;                                                                                 \
        default:                                                                                   \
            ret = -1;                                                                              \
        };                                                                                         \
        dst = _dst;                                                                                \
        barrier();                                                                                 \
        ret;                                                                                       \
    })

// value is replaced later by `probe_fill_relos()`
#define DECL_FUNC_RET(func) const volatile int ret__##func##__ = 0;
#define FUNC_RET_READ(type, func)                                                                  \
    ({                                                                                             \
        type _ret;                                                                                 \
        bpf_core_read(&_ret, sizeof(_ret), ctx + ret__##func##__);                                 \
        _ret;                                                                                      \
    })

#define DECL_FUNC_ARG_EXISTS(func, arg) const volatile bool exists__##func##__##arg##__ = false;
#define FUNC_ARG_EXISTS(func, arg) exists__##func##__##arg##__

#define DECL_FIELD_OFFSET(struct, field) const volatile int off__##struct##__##field##__ = 0;
#define FIELD_OFFSET(struct, field) off__##struct##__##field##__

// From linux/err.h
#define MAX_ERRNO 4095

// From include/linux/tty_driver.h
#define TTY_DRIVER_TYPE_PTY 0x0004
#define PTY_TYPE_MASTER 0x0001

// From include/uapi/asm-generic/termbits.h
#define ECHO 0x00008

static bool IS_ERR_OR_NULL(const void *ptr)
{
    return (!ptr) || (unsigned long)ptr >= (unsigned long)-MAX_ERRNO;
}

// Wrapper around bpf_probe_read_kernel_str that reads an empty string upon a read failure
static long read_kernel_str_or_empty_str(void *dst, int size, const void *unsafe_ptr)
{
    long ret = bpf_probe_read_kernel_str(dst, size, unsafe_ptr);
    if (ret < 0) {
        ((char *)dst)[0] = '\0';
        return 1;
    }

    return ret;
}

static long ebpf_argv__fill(char *buf, size_t buf_size, const struct task_struct *task)
{
    unsigned long start, end, size;

    start = BPF_CORE_READ(task, mm, arg_start);
    end   = BPF_CORE_READ(task, mm, arg_end);

    if (end <= start) {
        buf[0] = '\0';
        return 1;
    }

    size = end - start;
    size = size > buf_size ? buf_size : size;

    bpf_probe_read_user(buf, size, (void *)start);

    // Prevent final arg from being unterminated if buf is too small for args
    buf[size - 1] = '\0';

    return size;
}

static long ebpf_env__fill(char *buf, size_t buf_size, const struct task_struct *task)
{
    unsigned long start, end, size;

    start = BPF_CORE_READ(task, mm, env_start);
    end   = BPF_CORE_READ(task, mm, env_end);

    if (end <= start) {
        buf[0] = '\0';
        return 1;
    }

    size = end - start;
    size = size > buf_size ? buf_size : size;

    bpf_probe_read_user(buf, size, (void *)start);

    // Prevent final env from being unterminated if buf is too small for envs
    buf[size - 1] = '\0';

    return size;
}

static void ebpf_tty_dev__fill(struct ebpf_tty_dev *tty_dev, const struct tty_struct *tty)
{
    tty_dev->major = BPF_CORE_READ(tty, driver, major);
    tty_dev->minor = BPF_CORE_READ(tty, driver, minor_start);
    tty_dev->minor += BPF_CORE_READ(tty, index);

    struct winsize winsize     = BPF_CORE_READ(tty, winsize);
    struct ebpf_tty_winsize ws = {};
    ws.rows                    = winsize.ws_row;
    ws.cols                    = winsize.ws_col;
    tty_dev->winsize           = ws;

    struct ktermios termios   = BPF_CORE_READ(tty, termios);
    struct ebpf_tty_termios t = {};
    t.c_iflag                 = termios.c_iflag;
    t.c_oflag                 = termios.c_oflag;
    t.c_lflag                 = termios.c_lflag;
    t.c_cflag                 = termios.c_cflag;
    tty_dev->termios          = t;
}

static void ebpf_ctty__fill(struct ebpf_tty_dev *ctty, const struct task_struct *task)
{
    struct tty_struct *tty = BPF_CORE_READ(task, signal, tty);
    ebpf_tty_dev__fill(ctty, tty);
}

static void ebpf_pid_info__fill(struct ebpf_pid_info *pi, const struct task_struct *task)
{
    int e_pgid, e_sid;

    if (bpf_core_enum_value_exists(enum pid_type, PIDTYPE_PGID))
        e_pgid = bpf_core_enum_value(enum pid_type, PIDTYPE_PGID);
    else
        e_pgid = PIDTYPE_PGID;
    if (bpf_core_enum_value_exists(enum pid_type, PIDTYPE_SID))
        e_sid = bpf_core_enum_value(enum pid_type, PIDTYPE_SID);
    else
        e_sid = PIDTYPE_SID;
    pi->tid           = BPF_CORE_READ(task, pid);
    pi->tgid          = BPF_CORE_READ(task, tgid);
    pi->ppid          = BPF_CORE_READ(task, group_leader, real_parent, tgid);
    pi->pgid          = BPF_CORE_READ(task, group_leader, signal, pids[e_pgid], numbers[0].nr);
    pi->sid           = BPF_CORE_READ(task, group_leader, signal, pids[e_sid], numbers[0].nr);
    pi->start_time_ns = BPF_CORE_READ(task, group_leader, start_time);
}

static void ebpf_cred_info__fill(struct ebpf_cred_info *ci, const struct task_struct *task)
{
    ci->ruid = BPF_CORE_READ(task, cred, uid.val);
    ci->euid = BPF_CORE_READ(task, cred, euid.val);
    ci->suid = BPF_CORE_READ(task, cred, suid.val);
    ci->rgid = BPF_CORE_READ(task, cred, gid.val);
    ci->egid = BPF_CORE_READ(task, cred, egid.val);
    ci->sgid = BPF_CORE_READ(task, cred, sgid.val);

    // This check is to determine when the kernel_cap_t definition changed.
    //
    // Previously it was:
    // typedef struct kernel_cap_struct {
    //    __u32 cap[_KERNEL_CAPABILITY_U32S];
    // } kernel_cap_t;
    //
    // Currently it is:
    // typedef struct { u64 val; } kernel_cap_t;
    //
    // See https://github.com/torvalds/linux/commit/f122a08b197d076ccf136c73fae0146875812a88
    //
    if (bpf_core_field_exists(task->cred->cap_permitted.cap)) {
        kernel_cap_t dest;

        dest.cap[0]       = 0;
        dest.cap[1]       = 0;
        dest              = BPF_CORE_READ(task, cred, cap_permitted);
        ci->cap_permitted = (((u64)dest.cap[1]) << 32) + dest.cap[0];

        dest.cap[0]       = 0;
        dest.cap[1]       = 0;
        dest              = BPF_CORE_READ(task, cred, cap_effective);
        ci->cap_effective = (((u64)dest.cap[1]) << 32) + dest.cap[0];
    } else {
        const struct cred *cred = BPF_CORE_READ(task, cred);
        const void *cap         = NULL;

        struct new_kernel_cap_struct {
            u64 val;
        } dest;

        dest.val = 0;
        cap      = &cred->cap_permitted;
        bpf_core_read(&dest, sizeof(struct new_kernel_cap_struct), cap);
        ci->cap_permitted = dest.val;

        dest.val = 0;
        cap      = &cred->cap_effective;
        bpf_core_read(&dest, sizeof(struct new_kernel_cap_struct), cap);
        ci->cap_effective = dest.val;
    }
}

static void ebpf_comm__fill(char *comm, size_t len, const struct task_struct *task)
{
    read_kernel_str_or_empty_str(comm, len, BPF_CORE_READ(task, comm));
}

static void ebpf_ns__fill(struct ebpf_namespace_info *nsi, const struct task_struct *task)
{
    struct pid *pid;
    int pid_level;

    nsi->uts_inonum    = BPF_CORE_READ(task, nsproxy, uts_ns, ns.inum);
    nsi->ipc_inonum    = BPF_CORE_READ(task, nsproxy, ipc_ns, ns.inum);
    nsi->mnt_inonum    = BPF_CORE_READ(task, nsproxy, mnt_ns, ns.inum);
    nsi->net_inonum    = BPF_CORE_READ(task, nsproxy, net_ns, ns.inum);
    nsi->cgroup_inonum = BPF_CORE_READ(task, nsproxy, cgroup_ns, ns.inum);
    nsi->time_inonum   = BPF_CORE_READ(task, nsproxy, time_ns, ns.inum);

    pid = BPF_CORE_READ(task, thread_pid);
    if (pid == NULL) {
        nsi->pid_inonum = 0;
        return;
    }
    pid_level       = BPF_CORE_READ(pid, level);
    nsi->pid_inonum = BPF_CORE_READ(pid, numbers[pid_level].ns, ns.inum);
}

struct {
    __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
    __type(key, u32);
    __type(value, struct ebpf_event_stats);
    __uint(max_entries, 1);
} ringbuf_stats SEC(".maps");

static long ebpf_ringbuf_write(void *ringbuf, void *data, u64 size, u64 flags)
{
    long r;
    struct ebpf_event_stats *ees;
    u32 zero = 0;

    r   = bpf_ringbuf_output(ringbuf, data, size, flags);
    ees = bpf_map_lookup_elem(&ringbuf_stats, &zero);
    if (ees != NULL)
        r == 0 ? ees->sent++ : ees->lost++;

    return (r);
}

static bool is_kernel_thread(const struct task_struct *task)
{
    // All kernel threads are children of kthreadd, which always has pid 2
    // except on some ancient kernels (2.4x)
    // https://unix.stackexchange.com/a/411175
    return BPF_CORE_READ(task, group_leader, real_parent, tgid) == 2;
}

static bool is_thread_group_leader(const struct task_struct *task)
{
    return BPF_CORE_READ(task, pid) == BPF_CORE_READ(task, tgid);
}

static bool is_consumer()
{
    int pid = bpf_get_current_pid_tgid() >> 32;
    return consumer_pid == pid;
}

static int strncmp(const char *s1, const char *s2, size_t n)
{

    if (n == 0)
        return (0);
    do {
        if (*s1 != *s2++)
            return (*(unsigned char *)s1 - *(unsigned char *)--s2);
        if (*s1++ == 0)
            break;
    } while (--n != 0);
    return (0);
}

// compares first 'len' characters of str1 and str2, returns 1 if equal
// NOTE: no bounds check, assumes use under eBPF verifier
static int is_equal_prefix(const char *str1, const char *str2, int len)
{
    return !strncmp(str1, str2, len);
}

static u64 bpf_ktime_get_boot_ns_helper()
{
    if (bpf_core_enum_value_exists(enum bpf_func_id, BPF_FUNC_ktime_get_boot_ns))
        return bpf_ktime_get_boot_ns();
    else
        return 0;
}

#endif // EBPF_EVENTPROBE_HELPERS_H