execstack - tool to set, clear, or query executable stack flag of ELF binaries
and shared libraries
execstack [OPTION...] [FILES]
is a program which sets, clears, or queries executable stack
flag of ELF binaries and shared libraries. Linux has in the past allowed
execution of instructions on the stack and there are lots of binaries and
shared libraries assuming this behaviour. Furthermore, GCC trampoline code for
e.g. nested functions requires executable stack on many architectures. To
avoid breaking binaries and shared libraries which need executable stack, ELF
binaries and shared libraries now can be marked as requiring executable stack
or not requiring it. This marking is done through the p_flags field in the
PT_GNU_STACK program header entry. If the marking is missing, kernel or
dynamic linker need to assume it might need executable stack. The marking is
done automatically by recent GCC versions (objects using trampolines on the
stack are marked as requiring executable stack, all other newly built objects
are marked as not requiring it) and linker collects these markings into
marking of the whole binary or shared library. The user can override this at
assembly time (through --execstack
options), at link time (through -z execstack
or -z noexecstack
linker options) and using the execstack
tool also on an already linker
binary or shared library. This tool is especially useful for third party
shared libraries where it is known that they don't need executable stack or
testing proves it.
- -s --set-execstack
- Mark binary or shared library as requiring executable
- -c --clear-execstack
- Mark binary or shared library as not requiring executable
- -q --query
- Query executable stack marking of binaries and shared
libraries. For each file it prints either - when executable stack
is not required, X when executable stack is required or ?
when it is unknown whether the object requires or doesn't require
executable stack (the marking is missing).
- Print execstack version and exit.
- -? --help
- Print help message.
- Print a short usage message.
Command line arguments should be names of ELF binaries and shared libraries
which should be modified or queried.
# execstack -s ~/lib/libfoo.so.1
will mark ~/lib/libfoo.so.1 as requiring executable stack.
# execstack -c ~/bin/bar
will mark ~/bin/bar as not requiring executable stack.
# execstack -q ~/lib/libfoo.so.1
will query executable stack marking of the given files.
doesn't support yet marking of executables if they do not have
PT_GNU_STACK program header entry nor they have room for program segment
header table growth.
Jakub Jelinek <email@example.com>.