mem.c

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/*
 * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <init.h>
#include <os.h>

/* Modified by which_tmpdir, which is called during early boot */
static char *default_tmpdir = "/tmp";

/*
 *  Modified when creating the physical memory file and when checking
 * the tmp filesystem for usability, both happening during early boot.
 */
static char *tempdir = NULL;

static void __init find_tempdir(void)
{
    const char *dirs[] = { "TMP", "TEMP", "TMPDIR", NULL };
    int i;
    char *dir = NULL;

    if (tempdir != NULL)
        /* We've already been called */
        return;
    for (i = 0; dirs[i]; i++) {
        dir = getenv(dirs[i]);
        if ((dir != NULL) && (*dir != '\0'))
            break;
    }
    if ((dir == NULL) || (*dir == '\0'))
        dir = default_tmpdir;

    tempdir = malloc(strlen(dir) + 2);
    if (tempdir == NULL) {
        fprintf(stderr, "Failed to malloc tempdir, "
            "errno = %d\n", errno);
        return;
    }
    strcpy(tempdir, dir);
    strcat(tempdir, "/");
}

/*
 * This will return 1, with the first character in buf being the
 * character following the next instance of c in the file.  This will
 * read the file as needed.  If there's an error, -errno is returned;
 * if the end of the file is reached, 0 is returned.
 */
static int next(int fd, char *buf, size_t size, char c)
{
    ssize_t n;
    size_t len;
    char *ptr;

    while ((ptr = strchr(buf, c)) == NULL) {
        n = read(fd, buf, size - 1);
        if (n == 0)
            return 0;
        else if (n < 0)
            return -errno;

        buf[n] = '\0';
    }

    ptr++;
    len = strlen(ptr);
    memmove(buf, ptr, len + 1);

    /*
     * Refill the buffer so that if there's a partial string that we care
     * about, it will be completed, and we can recognize it.
     */
    n = read(fd, &buf[len], size - len - 1);
    if (n < 0)
        return -errno;

    buf[len + n] = '\0';
    return 1;
}

/* which_tmpdir is called only during early boot */
static int checked_tmpdir = 0;

/*
 * Look for a tmpfs mounted at /dev/shm.  I couldn't find a cleaner
 * way to do this than to parse /proc/mounts.  statfs will return the
 * same filesystem magic number and fs id for both /dev and /dev/shm
 * when they are both tmpfs, so you can't tell if they are different
 * filesystems.  Also, there seems to be no other way of finding the
 * mount point of a filesystem from within it.
 *
 * If a /dev/shm tmpfs entry is found, then we switch to using it.
 * Otherwise, we stay with the default /tmp.
 */
static void which_tmpdir(void)
{
    int fd, found;
    char buf[128] = { '\0' };

    if (checked_tmpdir)
        return;

    checked_tmpdir = 1;

    printf("Checking for tmpfs mount on /dev/shm...");

    fd = open("/proc/mounts", O_RDONLY);
    if (fd < 0) {
        printf("failed to open /proc/mounts, errno = %d\n", errno);
        return;
    }

    while (1) {
        found = next(fd, buf, ARRAY_SIZE(buf), ' ');
        if (found != 1)
            break;

        if (!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
            goto found;

        found = next(fd, buf, ARRAY_SIZE(buf), '\n');
        if (found != 1)
            break;
    }

err:
    if (found == 0)
        printf("nothing mounted on /dev/shm\n");
    else if (found < 0)
        printf("read returned errno %d\n", -found);

out:
    close(fd);

    return;

found:
    found = next(fd, buf, ARRAY_SIZE(buf), ' ');
    if (found != 1)
        goto err;

    if (strncmp(buf, "tmpfs", strlen("tmpfs"))) {
        printf("not tmpfs\n");
        goto out;
    }

    printf("OK\n");
    default_tmpdir = "/dev/shm";
    goto out;
}

static int __init make_tempfile(const char *template, char **out_tempname,
                int do_unlink)
{
    char *tempname;
    int fd;

    which_tmpdir();
    tempname = malloc(MAXPATHLEN);
    if (tempname == NULL)
        return -1;

    find_tempdir();
    if ((tempdir == NULL) || (strlen(tempdir) >= MAXPATHLEN))
        goto out;

    if (template[0] != '/')
        strcpy(tempname, tempdir);
    else
        tempname[0] = '\0';
    strncat(tempname, template, MAXPATHLEN-1-strlen(tempname));
    fd = mkstemp(tempname);
    if (fd < 0) {
        fprintf(stderr, "open - cannot create %s: %s\n", tempname,
            strerror(errno));
        goto out;
    }
    if (do_unlink && (unlink(tempname) < 0)) {
        perror("unlink");
        goto close;
    }
    if (out_tempname) {
        *out_tempname = tempname;
    } else
        free(tempname);
    return fd;
close:
    close(fd);
out:
    free(tempname);
    return -1;
}

#define TEMPNAME_TEMPLATE "vm_file-XXXXXX"

static int __init create_tmp_file(unsigned long long len)
{
    int fd, err;
    char zero;

    fd = make_tempfile(TEMPNAME_TEMPLATE, NULL, 1);
    if (fd < 0)
        exit(1);

    err = fchmod(fd, 0777);
    if (err < 0) {
        perror("fchmod");
        exit(1);
    }

    /*
     * Seek to len - 1 because writing a character there will
     * increase the file size by one byte, to the desired length.
     */
    if (lseek64(fd, len - 1, SEEK_SET) < 0) {
        perror("lseek64");
        exit(1);
    }

    zero = 0;

    err = write(fd, &zero, 1);
    if (err != 1) {
        perror("write");
        exit(1);
    }

    return fd;
}

int __init create_mem_file(unsigned long long len)
{
    int err, fd;

    fd = create_tmp_file(len);

    err = os_set_exec_close(fd);
    if (err < 0) {
        errno = -err;
        perror("exec_close");
    }
    return fd;
}


void __init check_tmpexec(void)
{
    void *addr;
    int err, fd = create_tmp_file(UM_KERN_PAGE_SIZE);

    addr = mmap(NULL, UM_KERN_PAGE_SIZE,
            PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, fd, 0);
    printf("Checking PROT_EXEC mmap in %s...",tempdir);
    fflush(stdout);
    if (addr == MAP_FAILED) {
        err = errno;
        perror("failed");
        close(fd);
        if (err == EPERM)
            printf("%s must be not mounted noexec\n",tempdir);
        exit(1);
    }
    printf("OK\n");
    munmap(addr, UM_KERN_PAGE_SIZE);

    close(fd);
}