tools/testing/selftests/x86/iopl.c

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