old-cross-binutils/gdb/common/linux-ptrace.c
Pedro Alves 8ae377e842 Always run the PTRACE_O_TRACESYSGOOD tests even if PTRACE_O_TRACEFORK is not supported.
If enabling PTRACE_O_TRACEFORK fails, we never test for
PTRACE_O_TRACESYSGOOD support.  Before PTRACE_O_TRACESYSGOOD is checked,
we have:

  /* First, set the PTRACE_O_TRACEFORK option.  If this fails, we
     know for sure that it is not supported.  */
  ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
		(PTRACE_TYPE_ARG4) PTRACE_O_TRACEFORK);

  if (ret != 0)
    {
      ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
		    (PTRACE_TYPE_ARG4) 0);
      if (ret != 0)
	{
	  warning (_("linux_check_ptrace_features: failed to kill child"));
	  return;
	}

      ret = my_waitpid (child_pid, &status, 0);
      if (ret != child_pid)
	warning (_("linux_check_ptrace_features: failed "
		   "to wait for killed child"));
      else if (!WIFSIGNALED (status))
	warning (_("linux_check_ptrace_features: unexpected "
		   "wait status 0x%x from killed child"), status);

      return; <<<<<<<<<<<<<<<<<
    }

Note that early return.  If PTRACE_O_TRACEFORK isn't supported, we're
not checking PTRACE_O_TRACESYSGOOD.  This didn't use to be a problem
before the unification of this whole detection business in
linux-ptrace.c.  Before, the sysgood detection was completely
separate:

static void
linux_test_for_tracesysgood (int original_pid)
{
  int ret;
  sigset_t prev_mask;

  /* We don't want those ptrace calls to be interrupted.  */
  block_child_signals (&prev_mask);

  linux_supports_tracesysgood_flag = 0;

  ret = ptrace (PTRACE_SETOPTIONS, original_pid, 0, PTRACE_O_TRACESYSGOOD);
  if (ret != 0)
    goto out;

  linux_supports_tracesysgood_flag = 1;
out:
  restore_child_signals_mask (&prev_mask);
}

So we need to get back the decoupling somehow.  I think it's cleaner
to split the seperate feature detections to separate functions.  This
patch does that.  The new functions are named for their counterparts
that existed before this code was moved to linux-ptrace.c.

Note I've used forward declarations for the new functions to make the
patch clearer, as otherwise the patch would look like I'd be adding a
bunch of new code.  A reorder can be done in a follow up patch.

Tested on x86_64 Fedora 17.

gdb/
2013-10-03  Pedro Alves  <palves@redhat.com>

	* common/linux-ptrace.c (linux_check_ptrace_features): Factor out
	the PTRACE_O_TRACESYSGOOD and PTRACE_O_TRACEFORK to separate
	functions.  Always test for PTRACE_O_TRACESYSGOOD even if
	PTRACE_O_TRACEFORK is not supported.
	(linux_test_for_tracesysgood): New function.
	(linux_test_for_tracefork): New function, factored out from
	linux_check_ptrace_features, and also don't kill child_pid here.
2013-10-03 10:13:34 +00:00

544 lines
16 KiB
C

/* Linux-specific ptrace manipulation routines.
Copyright (C) 2012-2013 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifdef GDBSERVER
#include "server.h"
#else
#include "defs.h"
#include "gdb_string.h"
#endif
#include "linux-ptrace.h"
#include "linux-procfs.h"
#include "nat/linux-waitpid.h"
#include "buffer.h"
#include "gdb_assert.h"
#include "gdb_wait.h"
#include <stdint.h>
/* Stores the currently supported ptrace options. A value of
-1 means we did not check for features yet. A value of 0 means
there are no supported features. */
static int current_ptrace_options = -1;
/* Find all possible reasons we could fail to attach PID and append these
newline terminated reason strings to initialized BUFFER. '\0' termination
of BUFFER must be done by the caller. */
void
linux_ptrace_attach_warnings (pid_t pid, struct buffer *buffer)
{
pid_t tracerpid;
tracerpid = linux_proc_get_tracerpid (pid);
if (tracerpid > 0)
buffer_xml_printf (buffer, _("warning: process %d is already traced "
"by process %d\n"),
(int) pid, (int) tracerpid);
if (linux_proc_pid_is_zombie (pid))
buffer_xml_printf (buffer, _("warning: process %d is a zombie "
"- the process has already terminated\n"),
(int) pid);
}
#if defined __i386__ || defined __x86_64__
/* Address of the 'ret' instruction in asm code block below. */
extern void (linux_ptrace_test_ret_to_nx_instr) (void);
#include <sys/reg.h>
#include <sys/mman.h>
#include <signal.h>
#endif /* defined __i386__ || defined __x86_64__ */
/* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
Test also x86_64 arch for PaX support. */
static void
linux_ptrace_test_ret_to_nx (void)
{
#if defined __i386__ || defined __x86_64__
pid_t child, got_pid;
gdb_byte *return_address, *pc;
long l;
int status, kill_status;
return_address = mmap (NULL, 2, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (return_address == MAP_FAILED)
{
warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
strerror (errno));
return;
}
/* Put there 'int3'. */
*return_address = 0xcc;
child = fork ();
switch (child)
{
case -1:
warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
strerror (errno));
return;
case 0:
l = ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) NULL,
(PTRACE_TYPE_ARG4) NULL);
if (l != 0)
warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
strerror (errno));
else
{
#if defined __i386__
asm volatile ("pushl %0;"
".globl linux_ptrace_test_ret_to_nx_instr;"
"linux_ptrace_test_ret_to_nx_instr:"
"ret"
: : "r" (return_address) : "%esp", "memory");
#elif defined __x86_64__
asm volatile ("pushq %0;"
".globl linux_ptrace_test_ret_to_nx_instr;"
"linux_ptrace_test_ret_to_nx_instr:"
"ret"
: : "r" ((uint64_t) (uintptr_t) return_address)
: "%rsp", "memory");
#else
# error "!__i386__ && !__x86_64__"
#endif
gdb_assert_not_reached ("asm block did not terminate");
}
_exit (1);
}
errno = 0;
got_pid = waitpid (child, &status, 0);
if (got_pid != child)
{
warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
(long) got_pid, strerror (errno));
return;
}
if (WIFSIGNALED (status))
{
if (WTERMSIG (status) != SIGKILL)
warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
(int) WTERMSIG (status));
else
warning (_("Cannot call inferior functions, Linux kernel PaX "
"protection forbids return to non-executable pages!"));
return;
}
if (!WIFSTOPPED (status))
{
warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
status);
return;
}
/* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
if (WSTOPSIG (status) != SIGTRAP && WSTOPSIG (status) != SIGSEGV)
{
warning (_("linux_ptrace_test_ret_to_nx: "
"WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
(int) WSTOPSIG (status));
return;
}
errno = 0;
#if defined __i386__
l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (EIP * 4),
(PTRACE_TYPE_ARG4) NULL);
#elif defined __x86_64__
l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (RIP * 8),
(PTRACE_TYPE_ARG4) NULL);
#else
# error "!__i386__ && !__x86_64__"
#endif
if (errno != 0)
{
warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
strerror (errno));
return;
}
pc = (void *) (uintptr_t) l;
kill (child, SIGKILL);
ptrace (PTRACE_KILL, child, (PTRACE_TYPE_ARG3) NULL,
(PTRACE_TYPE_ARG4) NULL);
errno = 0;
got_pid = waitpid (child, &kill_status, 0);
if (got_pid != child)
{
warning (_("linux_ptrace_test_ret_to_nx: "
"PTRACE_KILL waitpid returned %ld: %s"),
(long) got_pid, strerror (errno));
return;
}
if (!WIFSIGNALED (kill_status))
{
warning (_("linux_ptrace_test_ret_to_nx: "
"PTRACE_KILL status %d is not WIFSIGNALED!"),
status);
return;
}
/* + 1 is there as x86* stops after the 'int3' instruction. */
if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1)
{
/* PASS */
return;
}
/* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
if (WSTOPSIG (status) == SIGSEGV && pc == return_address)
{
/* PASS */
return;
}
if ((void (*) (void)) pc != &linux_ptrace_test_ret_to_nx_instr)
warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
"address %p nor is the return instruction %p!"),
pc, return_address, &linux_ptrace_test_ret_to_nx_instr);
else
warning (_("Cannot call inferior functions on this system - "
"Linux kernel with broken i386 NX (non-executable pages) "
"support detected!"));
#endif /* defined __i386__ || defined __x86_64__ */
}
/* Helper function to fork a process and make the child process call
the function FUNCTION, passing CHILD_STACK as parameter.
For MMU-less targets, clone is used instead of fork, and
CHILD_STACK is used as stack space for the cloned child. If NULL,
stack space is allocated via malloc (and subsequently passed to
FUNCTION). For MMU targets, CHILD_STACK is ignored. */
static int
linux_fork_to_function (gdb_byte *child_stack, void (*function) (gdb_byte *))
{
int child_pid;
/* Sanity check the function pointer. */
gdb_assert (function != NULL);
#if defined(__UCLIBC__) && defined(HAS_NOMMU)
#define STACK_SIZE 4096
if (child_stack == NULL)
child_stack = xmalloc (STACK_SIZE * 4);
/* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
#ifdef __ia64__
child_pid = __clone2 (function, child_stack, STACK_SIZE,
CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
#else /* !__ia64__ */
child_pid = clone (function, child_stack + STACK_SIZE,
CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
#endif /* !__ia64__ */
#else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
child_pid = fork ();
if (child_pid == 0)
function (NULL);
#endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
if (child_pid == -1)
perror_with_name (("fork"));
return child_pid;
}
/* A helper function for linux_check_ptrace_features, called after
the child forks a grandchild. */
static void
linux_grandchild_function (gdb_byte *child_stack)
{
/* Free any allocated stack. */
xfree (child_stack);
/* This code is only reacheable by the grandchild (child's child)
process. */
_exit (0);
}
/* A helper function for linux_check_ptrace_features, called after
the parent process forks a child. The child allows itself to
be traced by its parent. */
static void
linux_child_function (gdb_byte *child_stack)
{
ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0);
kill (getpid (), SIGSTOP);
/* Fork a grandchild. */
linux_fork_to_function (child_stack, linux_grandchild_function);
/* This code is only reacheable by the child (grandchild's parent)
process. */
_exit (0);
}
static void linux_test_for_tracesysgood (int child_pid);
static void linux_test_for_tracefork (int child_pid);
/* Determine ptrace features available on this target. */
static void
linux_check_ptrace_features (void)
{
int child_pid, ret, status;
/* Initialize the options. */
current_ptrace_options = 0;
/* Fork a child so we can do some testing. The child will call
linux_child_function and will get traced. The child will
eventually fork a grandchild so we can test fork event
reporting. */
child_pid = linux_fork_to_function (NULL, linux_child_function);
ret = my_waitpid (child_pid, &status, 0);
if (ret == -1)
perror_with_name (("waitpid"));
else if (ret != child_pid)
error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
ret);
if (! WIFSTOPPED (status))
error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
status);
linux_test_for_tracesysgood (child_pid);
linux_test_for_tracefork (child_pid);
/* Clean things up and kill any pending children. */
do
{
ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning (_("linux_check_ptrace_features: failed to kill child"));
my_waitpid (child_pid, &status, 0);
}
while (WIFSTOPPED (status));
}
/* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
syscalls. */
static void
linux_test_for_tracesysgood (int child_pid)
{
#ifdef GDBSERVER
/* gdbserver does not support PTRACE_O_TRACESYSGOOD. */
#else
int ret;
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) PTRACE_O_TRACESYSGOOD);
if (ret == 0)
current_ptrace_options |= PTRACE_O_TRACESYSGOOD;
#endif
}
/* Determine if PTRACE_O_TRACEFORK can be used to follow fork
events. */
static void
linux_test_for_tracefork (int child_pid)
{
int ret, status;
long second_pid;
/* First, set the PTRACE_O_TRACEFORK option. If this fails, we
know for sure that it is not supported. */
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) PTRACE_O_TRACEFORK);
if (ret != 0)
return;
#ifdef GDBSERVER
/* gdbserver does not support PTRACE_O_TRACEVFORKDONE yet. */
#else
/* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) (PTRACE_O_TRACEFORK
| PTRACE_O_TRACEVFORKDONE));
if (ret == 0)
current_ptrace_options |= PTRACE_O_TRACEVFORKDONE;
#endif
/* Setting PTRACE_O_TRACEFORK did not cause an error, however we
don't know for sure that the feature is available; old
versions of PTRACE_SETOPTIONS ignored unknown options.
Therefore, we attach to the child process, use PTRACE_SETOPTIONS
to enable fork tracing, and let it fork. If the process exits,
we assume that we can't use PTRACE_O_TRACEFORK; if we get the
fork notification, and we can extract the new child's PID, then
we assume that we can.
We do not explicitly check for vfork tracing here. It is
assumed that vfork tracing is available whenever fork tracing
is available. */
ret = ptrace (PTRACE_CONT, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning (_("linux_test_for_tracefork: failed to resume child"));
ret = my_waitpid (child_pid, &status, 0);
/* Check if we received a fork event notification. */
if (ret == child_pid && WIFSTOPPED (status)
&& status >> 16 == PTRACE_EVENT_FORK)
{
/* We did receive a fork event notification. Make sure its PID
is reported. */
second_pid = 0;
ret = ptrace (PTRACE_GETEVENTMSG, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) &second_pid);
if (ret == 0 && second_pid != 0)
{
int second_status;
/* We got the PID from the grandchild, which means fork
tracing is supported. */
#ifdef GDBSERVER
/* Do not enable all the options for now since gdbserver does not
properly support them. This restriction will be lifted when
gdbserver is augmented to support them. */
current_ptrace_options |= PTRACE_O_TRACECLONE;
#else
current_ptrace_options |= PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK
| PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC;
/* Do not enable PTRACE_O_TRACEEXIT until GDB is more prepared to
support read-only process state. */
#endif
/* Do some cleanup and kill the grandchild. */
my_waitpid (second_pid, &second_status, 0);
ret = ptrace (PTRACE_KILL, second_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning (_("linux_test_for_tracefork: "
"failed to kill second child"));
my_waitpid (second_pid, &status, 0);
}
}
else
warning (_("linux_test_for_tracefork: unexpected result from waitpid "
"(%d, status 0x%x)"), ret, status);
}
/* Enable reporting of all currently supported ptrace events. */
void
linux_enable_event_reporting (pid_t pid)
{
/* Check if we have initialized the ptrace features for this
target. If not, do it now. */
if (current_ptrace_options == -1)
linux_check_ptrace_features ();
/* Set the options. */
ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) (uintptr_t) current_ptrace_options);
}
/* Returns non-zero if PTRACE_OPTIONS is contained within
CURRENT_PTRACE_OPTIONS, therefore supported. Returns 0
otherwise. */
static int
ptrace_supports_feature (int ptrace_options)
{
gdb_assert (current_ptrace_options >= 0);
return ((current_ptrace_options & ptrace_options) == ptrace_options);
}
/* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
since they were all added to the kernel at the same time. */
int
linux_supports_tracefork (void)
{
return ptrace_supports_feature (PTRACE_O_TRACEFORK);
}
/* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
since they were all added to the kernel at the same time. */
int
linux_supports_traceclone (void)
{
return ptrace_supports_feature (PTRACE_O_TRACECLONE);
}
/* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
ptrace, 0 otherwise. */
int
linux_supports_tracevforkdone (void)
{
return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE);
}
/* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
0 otherwise. */
int
linux_supports_tracesysgood (void)
{
return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD);
}
/* Display possible problems on this system. Display them only once per GDB
execution. */
void
linux_ptrace_init_warnings (void)
{
static int warned = 0;
if (warned)
return;
warned = 1;
linux_ptrace_test_ret_to_nx ();
}