allocate.h

// SPDX-FileCopyrightText: Steven Ward
// SPDX-License-Identifier: MPL-2.0

/// Allocate private, anonymous memory using \c mmap
/**
* \file
* \author Steven Ward
* \sa https://man7.org/linux/man-pages/man2/mmap.2.html
* \sa https://man7.org/linux/man-pages/man2/madvise.2.html
* \sa https://github.com/google/boringssl/blob/master/SANDBOXING.md
* \sa https://github.com/aws/s2n-tls/blob/main/utils/s2n_fork_detection.c
*/

#pragma once

#include <err.h>
#include <stdlib.h>
#include <sys/mman.h>

#if defined(__cplusplus)
extern "C" {
#endif

/**
* \param len the number of bytes to allocate
* \return a pointer to the allocated memory
* \note This function terminates the calling process upon catastrophic error.
*/
static void*
allocate(const size_t len)
{
    constexpr int prot = PROT_READ | PROT_WRITE;
    constexpr int flags = MAP_PRIVATE | MAP_ANONYMOUS;

    void* addr = mmap(nullptr, len, prot, flags, -1, 0);

    if (addr == MAP_FAILED)
        err(EXIT_FAILURE, "mmap");

    if (madvise(addr, len, MADV_DONTDUMP) < 0)
        err(EXIT_FAILURE, "madvise");

    if (madvise(addr, len, MADV_WIPEONFORK) < 0)
        err(EXIT_FAILURE, "madvise");

    return addr;
}

#if defined(__cplusplus)
}
#endif