root/tools/testing/selftests/x86/iopl.c

DEFINITIONS

1. sethandler
2. sigsegv
3. main

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * iopl.c - Test case for a Linux on Xen 64-bit bug
   4  * Copyright (c) 2015 Andrew Lutomirski
   5  */
   6 
   7 #define _GNU_SOURCE
   8 #include <err.h>
   9 #include <stdio.h>
  10 #include <stdint.h>
  11 #include <signal.h>
  12 #include <setjmp.h>
  13 #include <stdlib.h>
  14 #include <string.h>
  15 #include <errno.h>
  16 #include <unistd.h>
  17 #include <sys/types.h>
  18 #include <sys/wait.h>
  19 #include <stdbool.h>
  20 #include <sched.h>
  21 #include <sys/io.h>
  22 
  23 static int nerrs = 0;
  24 
  25 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
  26                        int flags)
  27 {
  28         struct sigaction sa;
  29         memset(&sa, 0, sizeof(sa));
  30         sa.sa_sigaction = handler;
  31         sa.sa_flags = SA_SIGINFO | flags;
  32         sigemptyset(&sa.sa_mask);
  33         if (sigaction(sig, &sa, 0))
  34                 err(1, "sigaction");
  35 
  36 }
  37 
  38 static jmp_buf jmpbuf;
  39 
  40 static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
  41 {
  42         siglongjmp(jmpbuf, 1);
  43 }
  44 
  45 int main(void)
  46 {
  47         cpu_set_t cpuset;
  48         CPU_ZERO(&cpuset);
  49         CPU_SET(0, &cpuset);
  50         if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
  51                 err(1, "sched_setaffinity to CPU 0");
  52 
  53         /* Probe for iopl support.  Note that iopl(0) works even as nonroot. */
  54         if (iopl(3) != 0) {
  55                 printf("[OK]\tiopl(3) failed (%d) -- try running as root\n",
  56                        errno);
  57                 return 0;
  58         }
  59 
  60         /* Restore our original state prior to starting the test. */
  61         if (iopl(0) != 0)
  62                 err(1, "iopl(0)");
  63 
  64         pid_t child = fork();
  65         if (child == -1)
  66                 err(1, "fork");
  67 
  68         if (child == 0) {
  69                 printf("\tchild: set IOPL to 3\n");
  70                 if (iopl(3) != 0)
  71                         err(1, "iopl");
  72 
  73                 printf("[RUN]\tchild: write to 0x80\n");
  74                 asm volatile ("outb %%al, $0x80" : : "a" (0));
  75 
  76                 return 0;
  77         } else {
  78                 int status;
  79                 if (waitpid(child, &status, 0) != child ||
  80                     !WIFEXITED(status)) {
  81                         printf("[FAIL]\tChild died\n");
  82                         nerrs++;
  83                 } else if (WEXITSTATUS(status) != 0) {
  84                         printf("[FAIL]\tChild failed\n");
  85                         nerrs++;
  86                 } else {
  87                         printf("[OK]\tChild succeeded\n");
  88                 }
  89         }
  90 
  91         printf("[RUN]\tparent: write to 0x80 (should fail)\n");
  92 
  93         sethandler(SIGSEGV, sigsegv, 0);
  94         if (sigsetjmp(jmpbuf, 1) != 0) {
  95                 printf("[OK]\twrite was denied\n");
  96         } else {
  97                 asm volatile ("outb %%al, $0x80" : : "a" (0));
  98                 printf("[FAIL]\twrite was allowed\n");
  99                 nerrs++;
 100         }
 101 
 102         /* Test the capability checks. */
 103         printf("\tiopl(3)\n");
 104         if (iopl(3) != 0)
 105                 err(1, "iopl(3)");
 106 
 107         printf("\tDrop privileges\n");
 108         if (setresuid(1, 1, 1) != 0) {
 109                 printf("[WARN]\tDropping privileges failed\n");
 110                 goto done;
 111         }
 112 
 113         printf("[RUN]\tiopl(3) unprivileged but with IOPL==3\n");
 114         if (iopl(3) != 0) {
 115                 printf("[FAIL]\tiopl(3) should work if iopl is already 3 even if unprivileged\n");
 116                 nerrs++;
 117         }
 118 
 119         printf("[RUN]\tiopl(0) unprivileged\n");
 120         if (iopl(0) != 0) {
 121                 printf("[FAIL]\tiopl(0) should work if iopl is already 3 even if unprivileged\n");
 122                 nerrs++;
 123         }
 124 
 125         printf("[RUN]\tiopl(3) unprivileged\n");
 126         if (iopl(3) == 0) {
 127                 printf("[FAIL]\tiopl(3) should fail if when unprivileged if iopl==0\n");
 128                 nerrs++;
 129         } else {
 130                 printf("[OK]\tFailed as expected\n");
 131         }
 132 
 133 done:
 134         return nerrs ? 1 : 0;
 135 }
 136