239 lines
8.5 KiB
C++
239 lines
8.5 KiB
C++
/* Copyright (C) 2012-2020 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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/* This file is part of the vtable security feature implementation.
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The vtable security feature is designed to detect when a virtual
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call is about to be made through an invalid vtable pointer
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(possibly due to data corruption or malicious attacks).
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This file also contains the failure functions that get called when
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a vtable pointer is not found in the data set. Two particularly
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important functions are __vtv_verify_fail and __vtv_really_fail.
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They are both externally visible. __vtv_verify_fail is defined in
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such a way that it can be replaced by a programmer, if desired. It
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is the function that __VLTVerifyVtablePointer calls if it can't
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find the pointer in the data set. Allowing the programmer to
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overwrite this function means that he/she can do some alternate
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verification, including NOT failing in certain specific cases, if
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desired. This may be the case if the programmer has to deal wtih
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unverified third party software, for example. __vtv_really_fail is
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available for the programmer to call from his version of
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__vtv_verify_fail, if he decides the failure is real.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#if !defined (__CYGWIN__) && !defined (__MINGW32__)
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#include <execinfo.h>
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#endif
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#include <unistd.h>
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#include "vtv_utils.h"
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#include "vtv_fail.h"
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/* This is used to disable aborts for debugging purposes. */
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bool vtv_no_abort = false;
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extern "C" {
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/* __fortify_fail is a function in glibc that calls __libc_message,
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causing it to print out a program termination error message
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(including the name of the binary being terminated), a stack
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trace where the error occurred, and a memory map dump. Ideally
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we would have called __libc_message directly, but that function
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does not appear to be accessible to functions outside glibc,
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whereas __fortify_fail is. We call __fortify_fail from
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__vtv_really_fail. We looked at calling __libc_fatal, which is
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externally accessible, but it does not do the back trace and
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memory dump. */
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extern void __fortify_fail (const char *) __attribute__((noreturn));
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} /* extern "C" */
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const unsigned long SET_HANDLE_HANDLE_BIT = 0x2;
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/* Instantiate the template classes (in vtv_set.h) for our particular
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hash table needs. */
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typedef void * vtv_set_handle;
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typedef vtv_set_handle * vtv_set_handle_handle;
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static int vtv_failures_log_fd = -1;
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/* Open error logging file, if not already open, and write vtable
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verification failure messages (LOG_MSG) to the log file. Also
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generate a backtrace in the log file, if GENERATE_BACKTRACE is
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set. */
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static void
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log_error_message (const char *log_msg, bool generate_backtrace)
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{
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if (vtv_failures_log_fd == -1)
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vtv_failures_log_fd = vtv_open_log ("vtable_verification_failures.log");
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if (vtv_failures_log_fd == -1)
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return;
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vtv_add_to_log (vtv_failures_log_fd, "%s", log_msg);
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if (generate_backtrace)
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{
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#define STACK_DEPTH 20
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void *callers[STACK_DEPTH];
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#if !defined (__CYGWIN__) && !defined (__MINGW32__)
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int actual_depth = backtrace (callers, STACK_DEPTH);
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backtrace_symbols_fd (callers, actual_depth, vtv_failures_log_fd);
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#endif
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}
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}
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/* In the case where a vtable map variable is the only instance of the
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variable we have seen, it points directly to the set of valid
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vtable pointers. All subsequent instances of the 'same' vtable map
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variable point to the first vtable map variable. This function,
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given a vtable map variable PTR, checks a bit to see whether it's
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pointing directly to the data set or to the first vtable map
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variable. */
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static inline bool
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is_set_handle_handle (void * ptr)
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{
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return ((unsigned long) ptr & SET_HANDLE_HANDLE_BIT)
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== SET_HANDLE_HANDLE_BIT;
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}
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/* Returns the actual pointer value of a vtable map variable, PTR (see
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comments for is_set_handle_handle for more details). */
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static inline vtv_set_handle *
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ptr_from_set_handle_handle (void * ptr)
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{
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return (vtv_set_handle *) ((unsigned long) ptr & ~SET_HANDLE_HANDLE_BIT);
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}
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/* Given a vtable map variable, PTR, this function sets the bit that
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says this is the second (or later) instance of a vtable map
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variable. */
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static inline vtv_set_handle_handle
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set_handle_handle (vtv_set_handle * ptr)
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{
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return (vtv_set_handle_handle) ((unsigned long) ptr | SET_HANDLE_HANDLE_BIT);
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}
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/* This function is called from __VLTVerifyVtablePointerDebug; it
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sends as much debugging information as it can to the error log
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file, then calls __vtv_verify_fail. SET_HANDLE_PTR is the pointer
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to the set of valid vtable pointers, VTBL_PTR is the pointer that
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was not found in the set, and DEBUG_MSG is the message to be
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written to the log file before failing. n */
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void
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__vtv_verify_fail_debug (void **set_handle_ptr, const void *vtbl_ptr,
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const char *debug_msg)
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{
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log_error_message (debug_msg, false);
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/* Call the public interface in case it has been overwritten by
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user. */
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__vtv_verify_fail (set_handle_ptr, vtbl_ptr);
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log_error_message ("Returned from __vtv_verify_fail."
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" Secondary verification succeeded.\n", false);
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}
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/* This function calls __fortify_fail with a FAILURE_MSG and then
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calls abort. */
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void
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__vtv_really_fail (const char *failure_msg)
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{
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__fortify_fail (failure_msg);
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/* We should never get this far; __fortify_fail calls __libc_message
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which prints out a back trace and a memory dump and then is
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supposed to call abort, but let's play it safe anyway and call abort
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ourselves. */
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abort ();
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}
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/* This function takes an error MSG, a vtable map variable
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(DATA_SET_PTR) and a vtable pointer (VTBL_PTR). It is called when
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an attempt to verify VTBL_PTR with the set pointed to by
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DATA_SET_PTR failed. It outputs a failure message with the
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addresses involved, and calls __vtv_really_fail. */
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static void
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vtv_fail (const char *msg, void **data_set_ptr, const void *vtbl_ptr)
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{
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char buffer[128];
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int buf_len;
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const char *format_str =
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"*** Unable to verify vtable pointer (%p) in set (%p) *** \n";
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snprintf (buffer, sizeof (buffer), format_str, vtbl_ptr,
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is_set_handle_handle(*data_set_ptr) ?
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ptr_from_set_handle_handle (*data_set_ptr) :
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*data_set_ptr);
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buf_len = strlen (buffer);
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/* Send this to to stderr. */
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write (2, buffer, buf_len);
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if (!vtv_no_abort)
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__vtv_really_fail (msg);
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}
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/* Send information about what we were trying to do when verification
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failed to the error log, then call vtv_fail. This function can be
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overwritten/replaced by the user, to implement a secondary
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verification function instead. DATA_SET_PTR is the vtable map
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variable used for the failed verification, and VTBL_PTR is the
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vtable pointer that was not found in the set. */
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void
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__vtv_verify_fail (void **data_set_ptr, const void *vtbl_ptr)
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{
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char log_msg[256];
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snprintf (log_msg, sizeof (log_msg), "Looking for vtable %p in set %p.\n",
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vtbl_ptr,
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is_set_handle_handle (*data_set_ptr) ?
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ptr_from_set_handle_handle (*data_set_ptr) :
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*data_set_ptr);
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log_error_message (log_msg, false);
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const char *format_str =
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"*** Unable to verify vtable pointer (%p) in set (%p) *** \n";
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snprintf (log_msg, sizeof (log_msg), format_str, vtbl_ptr, *data_set_ptr);
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log_error_message (log_msg, false);
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log_error_message (" Backtrace: \n", true);
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const char *fail_msg = "Potential vtable pointer corruption detected!!\n";
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vtv_fail (fail_msg, data_set_ptr, vtbl_ptr);
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}
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