gdb/common/linux-ptrace.c

   1 /* Linux-specific ptrace manipulation routines.
   2    Copyright (C) 2012-2013 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #ifdef GDBSERVER
  20 #include "server.h"
  21 #else
  22 #include "defs.h"
  23 #include "gdb_string.h"
  24 #endif
  25
  26 #include "linux-ptrace.h"
  27 #include "linux-procfs.h"
  28 #include "buffer.h"
  29 #include "gdb_assert.h"
  30 #include "gdb_wait.h"
  31
  32 /* Find all possible reasons we could fail to attach PID and append these
  33    newline terminated reason strings to initialized BUFFER.  '\0' termination
  34    of BUFFER must be done by the caller.  */
  35
  36 void
  37 linux_ptrace_attach_warnings (pid_t pid, struct buffer *buffer)
  38 {
  39   pid_t tracerpid;
  40
  41   tracerpid = linux_proc_get_tracerpid (pid);
  42   if (tracerpid > 0)
  43     buffer_xml_printf (buffer, _("warning: process %d is already traced "
  44                                  "by process %d\n"),
  45                        (int) pid, (int) tracerpid);
  46
  47   if (linux_proc_pid_is_zombie (pid))
  48     buffer_xml_printf (buffer, _("warning: process %d is a zombie "
  49                                  "- the process has already terminated\n"),
  50                        (int) pid);
  51 }
  52
  53 #if defined __i386__ || defined __x86_64__
  54
  55 /* Address of the 'ret' instruction in asm code block below.  */
  56 extern void (linux_ptrace_test_ret_to_nx_instr) (void);
  57
  58 #include <sys/reg.h>
  59 #include <sys/mman.h>
  60 #include <signal.h>
  61 #include <stdint.h>
  62
  63 #endif /* defined __i386__ || defined __x86_64__ */
  64
  65 /* Test broken off-trunk Linux kernel patchset for NX support on i386.  It was
  66    removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
  67
  68    Test also x86_64 arch for PaX support.  */
  69
  70 static void
  71 linux_ptrace_test_ret_to_nx (void)
  72 {
  73 #if defined __i386__ || defined __x86_64__
  74   pid_t child, got_pid;
  75   gdb_byte *return_address, *pc;
  76   long l;
  77   int status, kill_status;
  78
  79   return_address = mmap (NULL, 2, PROT_READ | PROT_WRITE,
  80                          MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  81   if (return_address == MAP_FAILED)
  82     {
  83       warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
  84                strerror (errno));
  85       return;
  86     }
  87
  88   /* Put there 'int3'.  */
  89   *return_address = 0xcc;
  90
  91   child = fork ();
  92   switch (child)
  93     {
  94     case -1:
  95       warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
  96                strerror (errno));
  97       return;
  98
  99     case 0:
 100       l = ptrace (PTRACE_TRACEME, 0, NULL, NULL);
 101       if (l != 0)
 102         warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
 103                  strerror (errno));
 104       else
 105         {
 106 #if defined __i386__
 107           asm volatile ("pushl %0;"
 108                         ".globl linux_ptrace_test_ret_to_nx_instr;"
 109                         "linux_ptrace_test_ret_to_nx_instr:"
 110                         "ret"
 111                         : : "r" (return_address) : "%esp", "memory");
 112 #elif defined __x86_64__
 113           asm volatile ("pushq %0;"
 114                         ".globl linux_ptrace_test_ret_to_nx_instr;"
 115                         "linux_ptrace_test_ret_to_nx_instr:"
 116                         "ret"
 117                         : : "r" ((uint64_t) (uintptr_t) return_address)
 118                         : "%rsp", "memory");
 119 #else
 120 # error "!__i386__ && !__x86_64__"
 121 #endif
 122           gdb_assert_not_reached ("asm block did not terminate");
 123         }
 124
 125       _exit (1);
 126     }
 127
 128   errno = 0;
 129   got_pid = waitpid (child, &status, 0);
 130   if (got_pid != child)
 131     {
 132       warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
 133                (long) got_pid, strerror (errno));
 134       return;
 135     }
 136
 137   if (WIFSIGNALED (status))
 138     {
 139       if (WTERMSIG (status) != SIGKILL)
 140         warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
 141                  (int) WTERMSIG (status));
 142       else
 143         warning (_("Cannot call inferior functions, Linux kernel PaX "
 144                    "protection forbids return to non-executable pages!"));
 145       return;
 146     }
 147
 148   if (!WIFSTOPPED (status))
 149     {
 150       warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
 151                status);
 152       return;
 153     }
 154
 155   /* We may get SIGSEGV due to missing PROT_EXEC of the return_address.  */
 156   if (WSTOPSIG (status) != SIGTRAP && WSTOPSIG (status) != SIGSEGV)
 157     {
 158       warning (_("linux_ptrace_test_ret_to_nx: "
 159                  "WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
 160                (int) WSTOPSIG (status));
 161       return;
 162     }
 163
 164   errno = 0;
 165 #if defined __i386__
 166   l = ptrace (PTRACE_PEEKUSER, child, (void *) (uintptr_t) (EIP * 4), NULL);
 167 #elif defined __x86_64__
 168   l = ptrace (PTRACE_PEEKUSER, child, (void *) (uintptr_t) (RIP * 8), NULL);
 169 #else
 170 # error "!__i386__ && !__x86_64__"
 171 #endif
 172   if (errno != 0)
 173     {
 174       warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
 175                strerror (errno));
 176       return;
 177     }
 178   pc = (void *) (uintptr_t) l;
 179
 180   kill (child, SIGKILL);
 181   ptrace (PTRACE_KILL, child, NULL, NULL);
 182
 183   errno = 0;
 184   got_pid = waitpid (child, &kill_status, 0);
 185   if (got_pid != child)
 186     {
 187       warning (_("linux_ptrace_test_ret_to_nx: "
 188                  "PTRACE_KILL waitpid returned %ld: %s"),
 189                (long) got_pid, strerror (errno));
 190       return;
 191     }
 192   if (!WIFSIGNALED (kill_status))
 193     {
 194       warning (_("linux_ptrace_test_ret_to_nx: "
 195                  "PTRACE_KILL status %d is not WIFSIGNALED!"),
 196                status);
 197       return;
 198     }
 199
 200   /* + 1 is there as x86* stops after the 'int3' instruction.  */
 201   if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1)
 202     {
 203       /* PASS */
 204       return;
 205     }
 206
 207   /* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page.  */
 208   if (WSTOPSIG (status) == SIGSEGV && pc == return_address)
 209     {
 210       /* PASS */
 211       return;
 212     }
 213
 214   if ((void (*) (void)) pc != &linux_ptrace_test_ret_to_nx_instr)
 215     warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
 216                "address %p nor is the return instruction %p!"),
 217              pc, return_address, &linux_ptrace_test_ret_to_nx_instr);
 218   else
 219     warning (_("Cannot call inferior functions on this system - "
 220                "Linux kernel with broken i386 NX (non-executable pages) "
 221                "support detected!"));
 222 #endif /* defined __i386__ || defined __x86_64__ */
 223 }
 224
 225 /* Display possible problems on this system.  Display them only once per GDB
 226    execution.  */
 227
 228 void
 229 linux_ptrace_init_warnings (void)
 230 {
 231   static int warned = 0;
 232
 233   if (warned)
 234     return;
 235   warned = 1;
 236
 237   linux_ptrace_test_ret_to_nx ();
 238 }