/* Copyright (C) 2012-2015 Free Software Foundation, Inc. This file is part of GCC. GCC 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, or (at your option) any later version. GCC 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. Under Section 7 of GPL version 3, you are granted additional permissions described in the GCC Runtime Library Exception, version 3.1, as published by the Free Software Foundation. You should have received a copy of the GNU General Public License and a copy of the GCC Runtime Library Exception along with this program; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see <http://www.gnu.org/licenses/>. */ /* This file is part of the vtable security feature implementation. The vtable security feature is designed to detect when a virtual call is about to be made through an invalid vtable pointer (possibly due to data corruption or malicious attacks). This file also contains the failure functions that get called when a vtable pointer is not found in the data set. Two particularly important functions are __vtv_verify_fail and __vtv_really_fail. They are both externally visible. __vtv_verify_fail is defined in such a way that it can be replaced by a programmer, if desired. It is the function that __VLTVerifyVtablePointer calls if it can't find the pointer in the data set. Allowing the programmer to overwrite this function means that he/she can do some alternate verification, including NOT failing in certain specific cases, if desired. This may be the case if the programmer has to deal wtih unverified third party software, for example. __vtv_really_fail is available for the programmer to call from his version of __vtv_verify_fail, if he decides the failure is real. */ #include <stdlib.h> #include <stdio.h> #include <string.h> #if !defined (__CYGWIN__) && !defined (__MINGW32__) #include <execinfo.h> #endif #include <unistd.h> #include "vtv_utils.h" #include "vtv_fail.h" /* This is used to disable aborts for debugging purposes. */ bool vtv_no_abort = false; extern "C" { /* __fortify_fail is a function in glibc that calls __libc_message, causing it to print out a program termination error message (including the name of the binary being terminated), a stack trace where the error occurred, and a memory map dump. Ideally we would have called __libc_message directly, but that function does not appear to be accessible to functions outside glibc, whereas __fortify_fail is. We call __fortify_fail from __vtv_really_fail. We looked at calling __libc_fatal, which is externally accessible, but it does not do the back trace and memory dump. */ extern void __fortify_fail (const char *) __attribute__((noreturn)); } /* extern "C" */ const unsigned long SET_HANDLE_HANDLE_BIT = 0x2; /* Instantiate the template classes (in vtv_set.h) for our particular hash table needs. */ typedef void * vtv_set_handle; typedef vtv_set_handle * vtv_set_handle_handle; static int vtv_failures_log_fd = -1; /* Open error logging file, if not already open, and write vtable verification failure messages (LOG_MSG) to the log file. Also generate a backtrace in the log file, if GENERATE_BACKTRACE is set. */ static void log_error_message (const char *log_msg, bool generate_backtrace) { if (vtv_failures_log_fd == -1) vtv_failures_log_fd = vtv_open_log ("vtable_verification_failures.log"); if (vtv_failures_log_fd == -1) return; vtv_add_to_log (vtv_failures_log_fd, "%s", log_msg); if (generate_backtrace) { #define STACK_DEPTH 20 void *callers[STACK_DEPTH]; #if !defined (__CYGWIN__) && !defined (__MINGW32__) int actual_depth = backtrace (callers, STACK_DEPTH); backtrace_symbols_fd (callers, actual_depth, vtv_failures_log_fd); #endif } } /* In the case where a vtable map variable is the only instance of the variable we have seen, it points directly to the set of valid vtable pointers. All subsequent instances of the 'same' vtable map variable point to the first vtable map variable. This function, given a vtable map variable PTR, checks a bit to see whether it's pointing directly to the data set or to the first vtable map variable. */ static inline bool is_set_handle_handle (void * ptr) { return ((unsigned long) ptr & SET_HANDLE_HANDLE_BIT) == SET_HANDLE_HANDLE_BIT; } /* Returns the actual pointer value of a vtable map variable, PTR (see comments for is_set_handle_handle for more details). */ static inline vtv_set_handle * ptr_from_set_handle_handle (void * ptr) { return (vtv_set_handle *) ((unsigned long) ptr & ~SET_HANDLE_HANDLE_BIT); } /* Given a vtable map variable, PTR, this function sets the bit that says this is the second (or later) instance of a vtable map variable. */ static inline vtv_set_handle_handle set_handle_handle (vtv_set_handle * ptr) { return (vtv_set_handle_handle) ((unsigned long) ptr | SET_HANDLE_HANDLE_BIT); } /* This function is called from __VLTVerifyVtablePointerDebug; it sends as much debugging information as it can to the error log file, then calls __vtv_verify_fail. SET_HANDLE_PTR is the pointer to the set of valid vtable pointers, VTBL_PTR is the pointer that was not found in the set, and DEBUG_MSG is the message to be written to the log file before failing. n */ void __vtv_verify_fail_debug (void **set_handle_ptr, const void *vtbl_ptr, const char *debug_msg) { log_error_message (debug_msg, false); /* Call the public interface in case it has been overwritten by user. */ __vtv_verify_fail (set_handle_ptr, vtbl_ptr); log_error_message ("Returned from __vtv_verify_fail." " Secondary verification succeeded.\n", false); } /* This function calls __fortify_fail with a FAILURE_MSG and then calls abort. */ void __vtv_really_fail (const char *failure_msg) { __fortify_fail (failure_msg); /* We should never get this far; __fortify_fail calls __libc_message which prints out a back trace and a memory dump and then is supposed to call abort, but let's play it safe anyway and call abort ourselves. */ abort (); } /* This function takes an error MSG, a vtable map variable (DATA_SET_PTR) and a vtable pointer (VTBL_PTR). It is called when an attempt to verify VTBL_PTR with the set pointed to by DATA_SET_PTR failed. It outputs a failure message with the addresses involved, and calls __vtv_really_fail. */ static void vtv_fail (const char *msg, void **data_set_ptr, const void *vtbl_ptr) { char buffer[128]; int buf_len; const char *format_str = "*** Unable to verify vtable pointer (%p) in set (%p) *** \n"; snprintf (buffer, sizeof (buffer), format_str, vtbl_ptr, is_set_handle_handle(*data_set_ptr) ? ptr_from_set_handle_handle (*data_set_ptr) : *data_set_ptr); buf_len = strlen (buffer); /* Send this to to stderr. */ write (2, buffer, buf_len); if (!vtv_no_abort) __vtv_really_fail (msg); } /* Send information about what we were trying to do when verification failed to the error log, then call vtv_fail. This function can be overwritten/replaced by the user, to implement a secondary verification function instead. DATA_SET_PTR is the vtable map variable used for the failed verification, and VTBL_PTR is the vtable pointer that was not found in the set. */ void __vtv_verify_fail (void **data_set_ptr, const void *vtbl_ptr) { char log_msg[256]; snprintf (log_msg, sizeof (log_msg), "Looking for vtable %p in set %p.\n", vtbl_ptr, is_set_handle_handle (*data_set_ptr) ? ptr_from_set_handle_handle (*data_set_ptr) : *data_set_ptr); log_error_message (log_msg, false); const char *format_str = "*** Unable to verify vtable pointer (%p) in set (%p) *** \n"; snprintf (log_msg, sizeof (log_msg), format_str, vtbl_ptr, *data_set_ptr); log_error_message (log_msg, false); log_error_message (" Backtrace: \n", true); const char *fail_msg = "Potential vtable pointer corruption detected!!\n"; vtv_fail (fail_msg, data_set_ptr, vtbl_ptr); }