How to test whether a Linux binary was compiled as position independent code?
You can use the perl
script contained in the hardening-check
package, available in Fedora and Debian (as hardening-includes
). Read this Debian wiki page for details on what compile flags are checked. It's Debian specific, but the theory applies to Red Hat as well.
Example:
$ hardening-check $(which sshd)
/usr/sbin/sshd:
Position Independent Executable: yes
Stack protected: yes
Fortify Source functions: yes (some protected functions found)
Read-only relocations: yes
Immediate binding: yes
Simply use file
on the binary:
$ file ./pie-off
./pie-off: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=0dc3858e9f0334060bfebcbe3e854909191d8bdc, not stripped
$ file ./pie-on
./pie-on: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=962235df5bd188e1ec48c151ff61b6435d395f89, not stripped
Note the different type printed after the LSB information.
I used readelf --relocs
to test whether static or dynamic library is PIC on x86-64 the following way:
$ readelf --relocs /usr/lib/gcc/x86_64-linux-gnu/4.6/libstdc++.a |\
awk '$3~/^R_/ && $5!~/^\.debug/{print $3}' |sort -u
R_X86_64_32
R_X86_64_32S
R_X86_64_64
R_X86_64_DTPOFF32
R_X86_64_GOTPCREL
R_X86_64_PC32
R_X86_64_PLT32
R_X86_64_TLSLD
R_X86_64_TPOFF32
We see here R_X86_64_32
and R_X86_64_32S
. This means that the code is not position independent. When I rebuild a library with -fPIC I get:
$ readelf --relocs libstdc++.a |\
awk '$3~/^R_/ && $5!~/^\.debug/{print $3}' |sort -u
R_X86_64_64
R_X86_64_DTPOFF32
R_X86_64_GOTPCREL
R_X86_64_PC32
R_X86_64_PLT32
R_X86_64_TLSGD
R_X86_64_TLSLD
This method may probably work for executables, but I have not used it that way.