self-checksum

Program that calculates the checksum of its executable and read-only data memory. This is some example code that can be used if one wants to ensure that the program is not modified due to random bit flips while it's running or to generate a program identifier of the currently running program for some purposes.

This uses 64 bit xxHash library to calculate the checksum and glibc specific dl_iterate_phdr function to get the loaded shared objects. If you have 32 bit or less addressable architecture that has no unsigned long long type available, you need to find alternative hash function to 64 bit version of xxHash. For example 32 bit version of xxHash that also comes with this. If you have other C standard library than glibc in use, the working of this program depends on the availability of dl_iterate_phdr function.

Example

First let's check that what happens when we run this program two times:

$ ./self-checksum
d42b66204748ba3c
$ ./self-checksum
d42b66204748ba3c

The calculated checksum stays the same even when there is address space layout randomization in use, as the actual binary code from dynamically loaded libraries does not change. Then if we add another library to the program:

$ echo "void fun() {}" > fun.c
$ gcc -shared -fPIC fun.c -o fun.so
$ LD_PRELOAD=$PWD/fun.so ./self-checksum
9b1e4cafac0ecd41

The calculated checksum changes, as there is now one extra library with its own data loaded. If we then change the library contents, the calculated checksum will change:

$ echo "int fun() {return 1;}" > fun.c
$ gcc -shared -fPIC fun.c -o fun.so
$ LD_PRELOAD=$PWD/fun.so ./self-checksum
3234bd960dac2633

Building

cc --std=c99 -o self-checksum self-checksum.c xxhash.c

Or use the provide CMake build rules.