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start_up.c

/*
 * 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/ptrace.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <asm/unistd.h>
#include "init.h"
#include "kern_constants.h"
#include "os.h"
#include "mem_user.h"
#include "ptrace_user.h"
#include "registers.h"
#include "skas_ptrace.h"

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

      change_sig(SIGWINCH, 0);
      if (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(char *str)
{
      perror(str);
      exit(1);
}

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

      va_start(list, fmt);
      vprintf(fmt, list);
      va_end(list);
      fflush(stdout);

      exit(1);
}

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

      va_start(list, fmt);
      vprintf(fmt, list);
      va_end(list);
      fflush(stdout);
}

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)
            fatal_perror("stop_ptraced_child : ptrace failed");
      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 = 1;
int ptrace_ldt = 1;
int proc_mm = 1;
int skas_needs_stub = 0;

static int __init skas0_cmd_param(char *str, int* add)
{
      ptrace_faultinfo = proc_mm = 0;
      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 usage, so that SKAS0 is used, unless \n"
              "    you specify mode=tt.\n\n");

__uml_setup("mode=skas0", mode_skas0_cmd_param,
            "mode=skas0\n"
            "    Disables SKAS3 usage, so that SKAS0 is used, unless you \n"
            "    specify mode=tt. Note that this was recently added - on \n"
            "    older kernels you must use simply \"skas0\".\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",
                  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_POKEUSR, 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_ptrace: 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_ptrace : wait failed");

            if (WIFSTOPPED(status) &&
                (WSTOPSIG(status) == (SIGTRAP|0x80))) {
                  if (!count)
                        fatal("check_ptrace : SYSEMU_SINGLESTEP "
                              "doesn't singlestep");
                  n = ptrace(PTRACE_POKEUSR, 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
                  fatal("check_ptrace : expected SIGTRAP or "
                        "(SIGTRAP | 0x80), got status = %d", status);
      }
      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_PEEKUSR, pid, PT_SYSCALL_NR_OFFSET,
                         0);
            if (syscall == __NR_getpid) {
                  n = ptrace(PTRACE_POKEUSR, 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)
{
      /* 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();
}

static int __init noprocmm_cmd_param(char *str, int* add)
{
      proc_mm = 0;
      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)
{
      ptrace_faultinfo = 0;
      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)
{
      ptrace_ldt = 0;
      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) {
            ptrace_faultinfo = 0;
            if (errno == EIO)
                  non_fatal("not found\n");
            else
                  perror("not found");
      }
      else {
            if (!ptrace_faultinfo)
                  non_fatal("found but disabled on command line\n");
            else
                  non_fatal("found\n");
      }

      init_registers(pid);
      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");
            }
            ptrace_ldt = 0;
      }
      else {
            if (ptrace_ldt)
                  non_fatal("found\n");
            else
                  non_fatal("found, but use is disabled\n");
      }

      stop_ptraced_child(pid, 1, 1);
#else
      /* PTRACE_LDT might be disabled via cmdline option.
       * We want to override this, else we might use the stub
       * without real need
       */
      ptrace_ldt = 1;
#endif
}

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

int 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;

      return 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) {
            printf("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;
}

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