LCU14 201- Binary Analysis Tools

LCU14-201: Binary Analysis Tools
C. Lyon & O. Javaid, LCU14
LCU14 BURLINGAME

Binary analysis tools
● debug helpers: Sanitizers
● perf
● reverse debugging

Sanitizers: what are they?
● tools to help debug common programming errors
○ ASAN: AddressSanitizer
○ LSAN: LeakSanitizer
○ TSAN: ThreadSanitizer
○ MSAN: MemorySanitizer
○ UBSAN: UndefinedBehaviorSanitizer

Sanitizers
● generate instrumented code (unlike valgrind)
● errors are printed during execution
● use run-time libraries
○ override memory allocation functions
○ detect threads race conditions
● faster than valgrind

Sanitizers: ASAN
● memory error detector
● use after free
● heap/stack/global buffers overflows
● use after return
● double free/invalid free
● typical slowdown: ~2x

ASAN: how to use it
● -fsanitize=address compiler option
● interaction with gdb:
○ set a bkp on __asan_report_error or AsanDie
○ helper to describe a memory location
● run-time flags via ASAN_OPTIONS environment
variable

ASAN: example
int main(int argc, char **argv) {
int *array = new int[100];
delete [] array;
return array[argc]; // Use after free
}
$ g++ -g -fsanitize=address asan.cc -o asan.exe
$ ./asan.exe
=================================================================
==21981==ERROR: AddressSanitizer: heap-use-after-free on address 0x61400000fe44 at pc 0x400834 bp 0x7fff631c2030 sp
0x7fff631c2028
READ of size 4 at 0x61400000fe44 thread T0
#0 0x400833 in main /tmp/asan.cc:4
#1 0x3a3ae1ecdc in __libc_start_main (/lib64/libc.so.6+0x3a3ae1ecdc)
#2 0x4006b8 (/tmp/asan.exe+0x4006b8)
0x61400000fe44 is located 4 bytes inside of 400-byte region [0x61400000fe40,0x61400000ffd0)
freed by thread T0 here:
#0 0x7fa4b8268617 in operator delete[](void*) (/lib64/libasan.so.1+0x55617)
#1 0x4007e7 in main /tmp/asan.cc:3

Sanitizers: LSAN
● memory leak detector
● run-time ASAN option or -fsanitize=leak
compiler option
● no slowdown added to ASAN

LSAN: example
#include <stdlib.h>
void *p;
int main() {
p = malloc(7);
p = 0; // The memory is leaked here.
return 0;
}
$ gcc -g -fsanitize=leak lsan.c -o lsan.exe
$ ./lsan.exe
=================================================================
==24106==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 7 byte(s) in 1 object(s) allocated from:
#0 0x7fb12ee5c218 in malloc (/lib64/liblsan.so.0+0xb218)
#1 0x4006a5 in main /tmp/lsan.c:6
SUMMARY: LeakSanitizer: 7 byte(s) leaked in 1 allocation(s).

Sanitizers: TSAN
● data races detector
● similar to helgrind
● slowdown 5-15x
● -fsanitize=thread -fPIE -pie compiler
options

TSAN: example #include <pthread.h>
#include <stdio.h>
#include <string>
#include <map>
typedef std::map<std::string,
std::string> map_t;
void *threadfunc(void *p)
{
map_t& m = *(map_t*)p;
m["foo"] = "bar";
return 0;
}
$ g++ -g -fsanitize=thread tsan.cc -o tsan.exe -pie -fPIE
$ ./tsan.exe
foo=
==================
WARNING: ThreadSanitizer: data race (pid=24197)
Read of size 1 at 0x7d080000efd8 by thread T1:
int main() {
map_t m;
pthread_t t;
pthread_create(&t, 0, threadfunc, &m);
printf("foo=%sn", m["foo"].c_str());
pthread_join(t, 0);
}
#0 memcmp <null>:0 (libtsan.so.0+0x000000048e7d)
#1 std::string::compare(std::string const&) const <null>:0 (libstdc++.so.6+0x0000000bd9a2)
#2 std::less<std::string>::operator()(std::string const&, std::string const&) const /include/c++/4.9.0
/bits/stl_function.h:367 (tsan.exe+0x0000000018e3)
#3 std::_Rb_tree<std::string, std::pair<std::string const, std::string>, std::_Select1st<std::pair<std::string
const, std::string> >, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > >::
_M_lower_bound(std::_Rb_tree_node<std::pair<std::string const, std::string> >*, std::_Rb_tree_node<std::pair<std::

Sanitizers: MSAN
● uninitialized memory reads detector
● much faster than valgrind

Sanitizers: UBSAN
● undefined behavior checker
● -fsanitize=undefined compiler option

UBSAN: examples #include <stdio.h>
#include <limits.h>
int main() {
/* shift */
int i=1;
int j=33;
int k = i << j;
/* division by 0 */
i = 1;
j = 0;
k = i / j;
/* int_min / -1 */
i = INT_MIN;
j = -1;
k = i / j;
/* null */
int *ptr = NULL;
i = *ptr;
/* signed int overflow */
i = INT_MAX;
i++;
}
$ gcc -g -fsanitize=undefined ubsan.c -o ubsan.exe
$ ./ubsan.exe
ubsan.c:9:13: runtime error: shift exponent 33 is too large for 32-bit type 'int'
ubsan.c:15:9: runtime error: division by zero
ubsan.c:20:9: runtime error: division of -2147483648 by -1 cannot be represented in type 'int'
ubsan.c:25:5: runtime error: load of null pointer of type 'int'
ubsan.c:29:4: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'

Sanitizers: availability
● Developed by Google for LLVM
● Ported to GCC (on-going)
○ appeared in gcc-4.8 for x86_64
○ enablement needed target by target
● TSAN needs 64 bit pointers
○ won’t be available on Aarch32

Sanitizers: availability in GCC
ASAN LSAN TSAN UBSAN
i686 YES NO NO YES
x86_64 YES YES YES YES
AArch32 YES WONT[1] YES
AArch64 YES[2] YES[2]
MSAN is not available in GCC yet
LLVW has more options available than GCC
[1] TSAN requires 64 bit pointers
[2] ASAN/UBSAN enablement patch on AArch64 submitted b/o September

More about Linaro Connect: connect.linaro.org
Linaro members: www.linaro.org/members
More about Linaro: www.linaro.org/about/

GDB Reverse Debugging: An Introduction
● What is gdb record/replay?
● Record execution state of a program - Sufficient for reproducing execution.
● Store recorded state in a core file
● Replay recorded execution state
● What is reverse debugging?
● Ability to debug program backwards
● Allows you to step/continue backward in time
● Allows you set reverse breakpoints/watchpoints
● Allows to revert to an earlier execution state
● Reverse debugging with record/replay
● Start recording your program during execution
● Debug forward and backward during recording
● Debug forward and backward with replay

GDB Reverse Debugging: How It Works
● Forward vs Reverse
● Forward
● Operating system support for debugging - ptrace syscall (YES)
● Hardware support for debugging - Debug instructions, registers etc (YES)
● Hardware ability to trap, halt or break (YES)
● Reverse
● Going Back to future has its damages
● Operating System ability to reverse execution (NO)
● Hardware ability to go back in time (NO)
● What to do for reverse?
● Best possible reproduction of past execution state
● Process Data: Memory, Registers, Threads etc
● OS Data Structures: Processes, Threads etc
● Hardware State: Timing, cache, interrupts etc
● Maintain maximum possible cost benefit balance

GDB Reverse Debugging: How It Works
● What?
● GDB needs ability to store machine state
● GDB needs ability to revert to a past state
● How?
● After an instruction is executed
● Record registers that were modified
● Record memory location that were changed
● Keep record data in an memory buffer
● Save to a core file if replay/reverse is needed
● Revert registers and memory to step backwards
● Load saved record by loading core file

GDB Reverse Debugging: Commands Overview
● Reverse-Step (rs)
● Reverse-Continue (rc)
● Reverse-Finish
● Reverse-Next (rn)
● Reverse-Nexti
● Reverse-Stepi
● set exec-direction (forward/reverse)
● Break, Watch etc

GDB Reverse Debugging: Eclipse CDT UI
● Configuration UI

GDB Reverse Debugging: Eclipse CDT UI
● Run control UI

GDB Reverse Debugging: Some Use-Cases
● Significant speedup over cyclic debugging
STEPS
Forward
Reverse
Bug
Program Running
Reverse Debugging

GDB Reverse Debugging: Some Use-Cases
● Capture notorious bugs with record/replay
Program Running
Program Re-running
Program Re-running
STEPS
No Bug Occured
Program Running
No Bug Occured
Bug
Crash
Same
Bug
Program Running

GDB Reverse Debugging: Limitations
● Limited record log size
● Serial/sequential execution
● CPU overhead for saving/restoring state
● Does not restores system state
● Limitations for multi-threaded program and non-stop mode
● Not of much use for analysis of complex bugs
● Terminal/UI panic

GDB Reverse Debugging: In research
● Mozilla RR
● Record/Replay
● Reverse debugging
● Claims its more efficient than GDB
● Claims to debug complex applications like FireFox browser
● References
● http://www.gnu.org/software/gdb/news/reversible.html
● http://www.codeproject.com/Articles/235287/Reverse-Debugging-using-GDB
● https://sourceware.org/gdb/current/onlinedocs/gdb/Process-Record-and-Replay.html
● http://rr-project.org

Linux Perf Tools: An Overview
● What is PERF? (Performance Counters for Linux)
● Almost a superset of all tracing and profiling tools available on Linux
● Integrated with Linux kernel
● Hardware + Software + Trace + More
● Light weight profiling (Low Overhead)
● Not for tracing and profiling the kernel only
● Profile and trace user-space applications
● How PERF does it?
● Hardware: PMU (Performance Counters)
● Perf kernel module
● Perf user-space application

Linux Perf Tools: What perf can do for you...
● Why
● Your app or kernel consuming CPU?
● Your application is starving for CPU?
● Certain threads holding onto locks?
● Which
● Part of kernel/application code causing cache misses?
● Application consuming memory?
● What
● has caused driver performance downgrade?
● is average syscall handling overhead?
● cpu and memory optimizations are possible in your code?
● And a lot more...

Linux Perf Tools: Events
● Hardware Events
● cycles, branches, instructions etc
● cache-references, cache-misses etc
● Hardware Cache Event
● L1/L2 cache loads, stores, misses etc
● TLB loads, stores misses etc
● Software Events
● task-clock, page-faults, context-switches etc
● Kernel PMU Events
● cpu/branch-instructions
● cpu/cache-misses
● Trace Events

Linux Perf Tools: Perf coverage map
● Source: http://www.brendangregg.com/linuxperf.html

Linux Perf Tools: User Interface (Commands)
● Perf Installation on Ubuntu
● apt-get install linux-tools
● Commandline tools under perf
● record: Run a command and record its profile into perf.data
● report: Read perf.data (created by perf record) and display profile
● lock: Analyze lock events
● mem: Profile memory accesses
● timechart: Tool to visualize total system behavior during a workload
● top: System profiling tool
● trace: strace inspired tool
● probe: Define new dynamic tracepoints
● kmem: Tool to trace/measure kernel memory(slab) properties
● Write “perf” on commandline to get full list

Linux Perf Tools: User Interface (Graphical)
● Graphical UI
● Install the Perf plug-in for Eclipse
● http://www.eclipse.org/linuxtools/projectPages/perf/
● http://wiki.eclipse.org/Linux_Tools_Project/PERF/User_Guide
● Source: http://wiki.eclipse.org/Linux_Tools_Project/PERF/User_Guide

Linux Perf Tools: Sampling and analysis
● perf record
● perf record [options] [commandline] [arguments]
● Generates an output file called perf.data
● perf report
● reads perf.data
● generates a concise execution profile
● perf annotate
● Performs source level analysis
● Binary should be compiled with debug info
● List all raw events
● perf script (from perf.data by default)

Linux Perf Tools: Monitoring
● Counting events
● perf stat [application] [argument]
● Keeps a event count during process execution
● Displays a common list of events by default
● Can count specific events
● Both user and kernel level code
● Real-time monitoring: Perf Top
● “perf top” prints sampled functions in real time
● Configurable but shows all CPUs by default
● Shows user-level as well as kernel functions
● Show system calls by process, refreshing every 2 seconds
● perf top -e raw_syscalls:sys_enter -ns comm

Linux Perf Tools: Perf also supports
● Benchmarking
● Scripting
● Static Tracing
● Dynamic Tracing
● Much more..
source: http://www.brendangregg.com/perf_events

Linux Perf Tools: Concluding..
● Some other tools
● LTTNG
● SystemTAP
● gprof
● Perfctr
● oprofile
● Sysprof
● Dtrace
● References
● http://www.brendangregg.com/perf.html
● https://perf.wiki.kernel.org/index.php/Tutorial
● https://perf.wiki.kernel.org/index.php/Main_Page

Prelink: Some background first...
● Dynamic vs Static Linking
● Significantly reduced binary size
● Library code shared and updated without recompile
● But run time address calculation overhead
● More libraries means higher startup time
● Address binding to a fixed address: Not a good idea!!
● Overhead burden increases with frequent load/un-load
● Preload
● Load ahead of time based on frequency of use
● A daemon that runs in background
● Useful with frequently run program
● Requires constant extra space in memory
● Not for apps that are not unloaded frequently
● Caching may be doing the same already

Prelink: What it is?
● Speeds up application load time
● By reducing dynamic linking overhead
● But only for library dependent application like KDE, QT etc
● Pre-calculate dependencies
● Load libraries to preferred addresses
● Revert to dynamic linking if prelink fails.

Prelink: How it works?
● Use with Caution: It may mess your system up!
● How to set it up?
● Install prelink
● sudo apt-get install prelink
● Configure what to prelink
● edit /etc/default/prelink
● Enable by "PRELINKING=unknown” from “unknown" to "yes"
● Start a daily update
● /etc/cron.daily/prelink
● Undo by
● setting "PRELINKING=no” in /etc/default/prelink
● run /etc/cron.daily/prelink
● Run again whenever you update/install new stuff

Prelink: Is it worth the effort?
● Advantages
● Good for systems like Infotainment Systems, Set-Top-Boxes etc
● Provides significant speedup on application loading time
● Can undo/redo prelink
● Disadvantages
● ReLink required on package upgrade
● Predictable shared library locations (no ASLR)
● Modifies files which means MD5 mis-match
● Hard to maintain system integrity with frequent updates/changes
● References
● https://wiki.gentoo.org/wiki/Prelink

LCU14 201- Binary Analysis Tools

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LCU14 201- Binary Analysis Tools