start_up.c

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/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <signal.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <asm/unistd.h>
#include <init.h>
#include <os.h>
#include <mem_user.h>
#include <ptrace_user.h>
#include <registers.h>
#include <skas.h>
#include <skas_ptrace.h>

static void ptrace_child(void)
{
    int ret;
    /* Calling os_getpid because some libcs cached getpid incorrectly */
    int pid = os_getpid(), ppid = getppid();
    int sc_result;

    if (change_sig(SIGWINCH, 0) < 0 ||
        ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
        perror("ptrace");
        kill(pid, SIGKILL);
    }
    kill(pid, SIGSTOP);

    /*
     * This syscall will be intercepted by the parent. Don't call more than
     * once, please.
     */
    sc_result = os_getpid();

    if (sc_result == pid)
        /* Nothing modified by the parent, we are running normally. */
        ret = 1;
    else if (sc_result == ppid)
        /*
         * Expected in check_ptrace and check_sysemu when they succeed
         * in modifying the stack frame
         */
        ret = 0;
    else
        /* Serious trouble! This could be caused by a bug in host 2.6
         * SKAS3/2.6 patch before release -V6, together with a bug in
         * the UML code itself.
         */
        ret = 2;

    exit(ret);
}

static void fatal_perror(const char *str)
{
    perror(str);
    exit(1);
}

static void fatal(char *fmt, ...)
{
    va_list list;

    va_start(list, fmt);
    vfprintf(stderr, fmt, list);
    va_end(list);

    exit(1);
}

static void non_fatal(char *fmt, ...)
{
    va_list list;

    va_start(list, fmt);
    vfprintf(stderr, fmt, list);
    va_end(list);
}

static int start_ptraced_child(void)
{
    int pid, n, status;

    pid = fork();
    if (pid == 0)
        ptrace_child();
    else if (pid < 0)
        fatal_perror("start_ptraced_child : fork failed");

    CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
    if (n < 0)
        fatal_perror("check_ptrace : waitpid failed");
    if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
        fatal("check_ptrace : expected SIGSTOP, got status = %d",
              status);

    return pid;
}

/* When testing for SYSEMU support, if it is one of the broken versions, we
 * must just avoid using sysemu, not panic, but only if SYSEMU features are
 * broken.
 * So only for SYSEMU features we test mustpanic, while normal host features
 * must work anyway!
 */
static int stop_ptraced_child(int pid, int exitcode, int mustexit)
{
    int status, n, ret = 0;

    if (ptrace(PTRACE_CONT, pid, 0, 0) < 0) {
        perror("stop_ptraced_child : ptrace failed");
        return -1;
    }
    CATCH_EINTR(n = waitpid(pid, &status, 0));
    if (!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
        int exit_with = WEXITSTATUS(status);
        if (exit_with == 2)
            non_fatal("check_ptrace : child exited with status 2. "
                  "\nDisabling SYSEMU support.\n");
        non_fatal("check_ptrace : child exited with exitcode %d, while "
              "expecting %d; status 0x%x\n", exit_with,
              exitcode, status);
        if (mustexit)
            exit(1);
        ret = -1;
    }

    return ret;
}

/* Changed only during early boot */
int ptrace_faultinfo;
static int disable_ptrace_faultinfo;

int ptrace_ldt;
static int disable_ptrace_ldt;

int proc_mm;
static int disable_proc_mm;

int have_switch_mm;
static int disable_switch_mm;

int skas_needs_stub;

static int __init skas0_cmd_param(char *str, int* add)
{
    disable_ptrace_faultinfo = 1;
    disable_ptrace_ldt = 1;
    disable_proc_mm = 1;
    disable_switch_mm = 1;

    return 0;
}

/* The two __uml_setup would conflict, without this stupid alias. */

static int __init mode_skas0_cmd_param(char *str, int* add)
    __attribute__((alias("skas0_cmd_param")));

__uml_setup("skas0", skas0_cmd_param,
"skas0\n"
"    Disables SKAS3 and SKAS4 usage, so that SKAS0 is used\n\n");

__uml_setup("mode=skas0", mode_skas0_cmd_param,
"mode=skas0\n"
"    Disables SKAS3 and SKAS4 usage, so that SKAS0 is used.\n\n");

/* Changed only during early boot */
static int force_sysemu_disabled = 0;

static int __init nosysemu_cmd_param(char *str, int* add)
{
    force_sysemu_disabled = 1;
    return 0;
}

__uml_setup("nosysemu", nosysemu_cmd_param,
"nosysemu\n"
"    Turns off syscall emulation patch for ptrace (SYSEMU) on.\n"
"    SYSEMU is a performance-patch introduced by Laurent Vivier. It changes\n"
"    behaviour of ptrace() and helps reducing host context switch rate.\n"
"    To make it working, you need a kernel patch for your host, too.\n"
"    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
"    information.\n\n");

static void __init check_sysemu(void)
{
    unsigned long regs[MAX_REG_NR];
    int pid, n, status, count=0;

    non_fatal("Checking syscall emulation patch for ptrace...");
    sysemu_supported = 0;
    pid = start_ptraced_child();

    if (ptrace(PTRACE_SYSEMU, pid, 0, 0) < 0)
        goto fail;

    CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
    if (n < 0)
        fatal_perror("check_sysemu : wait failed");
    if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
        fatal("check_sysemu : expected SIGTRAP, got status = %d\n",
              status);

    if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
        fatal_perror("check_sysemu : PTRACE_GETREGS failed");
    if (PT_SYSCALL_NR(regs) != __NR_getpid) {
        non_fatal("check_sysemu got system call number %d, "
              "expected %d...", PT_SYSCALL_NR(regs), __NR_getpid);
        goto fail;
    }

    n = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_RET_OFFSET, os_getpid());
    if (n < 0) {
        non_fatal("check_sysemu : failed to modify system call "
              "return");
        goto fail;
    }

    if (stop_ptraced_child(pid, 0, 0) < 0)
        goto fail_stopped;

    sysemu_supported = 1;
    non_fatal("OK\n");
    set_using_sysemu(!force_sysemu_disabled);

    non_fatal("Checking advanced syscall emulation patch for ptrace...");
    pid = start_ptraced_child();

    if ((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
           (void *) PTRACE_O_TRACESYSGOOD) < 0))
        fatal_perror("check_sysemu: PTRACE_OLDSETOPTIONS failed");

    while (1) {
        count++;
        if (ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
            goto fail;
        CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
        if (n < 0)
            fatal_perror("check_sysemu: wait failed");

        if (WIFSTOPPED(status) &&
            (WSTOPSIG(status) == (SIGTRAP|0x80))) {
            if (!count) {
                non_fatal("check_sysemu: SYSEMU_SINGLESTEP "
                      "doesn't singlestep");
                goto fail;
            }
            n = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_RET_OFFSET,
                   os_getpid());
            if (n < 0)
                fatal_perror("check_sysemu : failed to modify "
                         "system call return");
            break;
        }
        else if (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP))
            count++;
        else {
            non_fatal("check_sysemu: expected SIGTRAP or "
                  "(SIGTRAP | 0x80), got status = %d\n",
                  status);
            goto fail;
        }
    }
    if (stop_ptraced_child(pid, 0, 0) < 0)
        goto fail_stopped;

    sysemu_supported = 2;
    non_fatal("OK\n");

    if (!force_sysemu_disabled)
        set_using_sysemu(sysemu_supported);
    return;

fail:
    stop_ptraced_child(pid, 1, 0);
fail_stopped:
    non_fatal("missing\n");
}

static void __init check_ptrace(void)
{
    int pid, syscall, n, status;

    non_fatal("Checking that ptrace can change system call numbers...");
    pid = start_ptraced_child();

    if ((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
           (void *) PTRACE_O_TRACESYSGOOD) < 0))
        fatal_perror("check_ptrace: PTRACE_OLDSETOPTIONS failed");

    while (1) {
        if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
            fatal_perror("check_ptrace : ptrace failed");

        CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
        if (n < 0)
            fatal_perror("check_ptrace : wait failed");

        if (!WIFSTOPPED(status) ||
           (WSTOPSIG(status) != (SIGTRAP | 0x80)))
            fatal("check_ptrace : expected (SIGTRAP|0x80), "
                   "got status = %d", status);

        syscall = ptrace(PTRACE_PEEKUSER, pid, PT_SYSCALL_NR_OFFSET,
                 0);
        if (syscall == __NR_getpid) {
            n = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
                   __NR_getppid);
            if (n < 0)
                fatal_perror("check_ptrace : failed to modify "
                         "system call");
            break;
        }
    }
    stop_ptraced_child(pid, 0, 1);
    non_fatal("OK\n");
    check_sysemu();
}

extern void check_tmpexec(void);

static void __init check_coredump_limit(void)
{
    struct rlimit lim;
    int err = getrlimit(RLIMIT_CORE, &lim);

    if (err) {
        perror("Getting core dump limit");
        return;
    }

    printf("Core dump limits :\n\tsoft - ");
    if (lim.rlim_cur == RLIM_INFINITY)
        printf("NONE\n");
    else printf("%lu\n", lim.rlim_cur);

    printf("\thard - ");
    if (lim.rlim_max == RLIM_INFINITY)
        printf("NONE\n");
    else printf("%lu\n", lim.rlim_max);
}

void __init os_early_checks(void)
{
    int pid;

    /* Print out the core dump limits early */
    check_coredump_limit();

    check_ptrace();

    /* Need to check this early because mmapping happens before the
     * kernel is running.
     */
    check_tmpexec();

    pid = start_ptraced_child();
    if (init_registers(pid))
        fatal("Failed to initialize default registers");
    stop_ptraced_child(pid, 1, 1);
}

static int __init noprocmm_cmd_param(char *str, int* add)
{
    disable_proc_mm = 1;
    return 0;
}

__uml_setup("noprocmm", noprocmm_cmd_param,
"noprocmm\n"
"    Turns off usage of /proc/mm, even if host supports it.\n"
"    To support /proc/mm, the host needs to be patched using\n"
"    the current skas3 patch.\n\n");

static int __init noptracefaultinfo_cmd_param(char *str, int* add)
{
    disable_ptrace_faultinfo = 1;
    return 0;
}

__uml_setup("noptracefaultinfo", noptracefaultinfo_cmd_param,
"noptracefaultinfo\n"
"    Turns off usage of PTRACE_FAULTINFO, even if host supports\n"
"    it. To support PTRACE_FAULTINFO, the host needs to be patched\n"
"    using the current skas3 patch.\n\n");

static int __init noptraceldt_cmd_param(char *str, int* add)
{
    disable_ptrace_ldt = 1;
    return 0;
}

__uml_setup("noptraceldt", noptraceldt_cmd_param,
"noptraceldt\n"
"    Turns off usage of PTRACE_LDT, even if host supports it.\n"
"    To support PTRACE_LDT, the host needs to be patched using\n"
"    the current skas3 patch.\n\n");

static inline void check_skas3_ptrace_faultinfo(void)
{
    struct ptrace_faultinfo fi;
    int pid, n;

    non_fatal("  - PTRACE_FAULTINFO...");
    pid = start_ptraced_child();

    n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
    if (n < 0) {
        if (errno == EIO)
            non_fatal("not found\n");
        else
            perror("not found");
    } else if (disable_ptrace_faultinfo)
        non_fatal("found but disabled on command line\n");
    else {
        ptrace_faultinfo = 1;
        non_fatal("found\n");
    }

    stop_ptraced_child(pid, 1, 1);
}

static inline void check_skas3_ptrace_ldt(void)
{
#ifdef PTRACE_LDT
    int pid, n;
    unsigned char ldtbuf[40];
    struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
        .func = 2, /* read default ldt */
        .ptr = ldtbuf,
        .bytecount = sizeof(ldtbuf)};

    non_fatal("  - PTRACE_LDT...");
    pid = start_ptraced_child();

    n = ptrace(PTRACE_LDT, pid, 0, (unsigned long) &ldt_op);
    if (n < 0) {
        if (errno == EIO)
            non_fatal("not found\n");
        else
            perror("not found");
    } else if (disable_ptrace_ldt)
        non_fatal("found, but use is disabled\n");
    else {
        ptrace_ldt = 1;
        non_fatal("found\n");
    }

    stop_ptraced_child(pid, 1, 1);
#endif
}

static inline void check_skas3_proc_mm(void)
{
    non_fatal("  - /proc/mm...");
    if (access("/proc/mm", W_OK) < 0)
        perror("not found");
    else if (disable_proc_mm)
        non_fatal("found but disabled on command line\n");
    else {
        proc_mm = 1;
        non_fatal("found\n");
    }
}

void can_do_skas(void)
{
    non_fatal("Checking for the skas3 patch in the host:\n");

    check_skas3_proc_mm();
    check_skas3_ptrace_faultinfo();
    check_skas3_ptrace_ldt();

    if (!proc_mm || !ptrace_faultinfo || !ptrace_ldt)
        skas_needs_stub = 1;
}

int __init parse_iomem(char *str, int *add)
{
    struct iomem_region *new;
    struct stat64 buf;
    char *file, *driver;
    int fd, size;

    driver = str;
    file = strchr(str,',');
    if (file == NULL) {
        fprintf(stderr, "parse_iomem : failed to parse iomem\n");
        goto out;
    }
    *file = '\0';
    file++;
    fd = open(file, O_RDWR, 0);
    if (fd < 0) {
        perror("parse_iomem - Couldn't open io file");
        goto out;
    }

    if (fstat64(fd, &buf) < 0) {
        perror("parse_iomem - cannot stat_fd file");
        goto out_close;
    }

    new = malloc(sizeof(*new));
    if (new == NULL) {
        perror("Couldn't allocate iomem_region struct");
        goto out_close;
    }

    size = (buf.st_size + UM_KERN_PAGE_SIZE) & ~(UM_KERN_PAGE_SIZE - 1);

    *new = ((struct iomem_region) { .next       = iomem_regions,
                    .driver     = driver,
                    .fd     = fd,
                    .size       = size,
                    .phys       = 0,
                    .virt       = 0 });
    iomem_regions = new;
    iomem_size += new->size + UM_KERN_PAGE_SIZE;

    return 0;
 out_close:
    close(fd);
 out:
    return 1;
}