How to control a program's default stack settings in BSD or Linux?

Question

Let's say I have a running program, and I look at /proc/[pid]/map in BSD (or /proc/[pid]/maps in linux), I'll see a line like:

0xbfbe0000 0xbfc00000 3 0 0xc74c4198 rwx 1 0 0x3000 COW NNC default - CH 1001

which is the stack. All my PC-BSD programs use this same stack boundary 0xbfc00000. On linux, with ASLR turned off, a similar thing happens.

I would like to play with these settings on some programs, but the stack doesn't even seem to be specified in the elf program headers or section headers.

So if I want to change the settings, such as:

• change execute permission of the stack
• set the stack boundary to another value

Is there a way to change the "stack setting" for an individual program? How about system wide?

Answer 1

For FreeBSD:

On amd64, i386 and powerpc you can control wether the stack is executable with the sysctls kern.elf32.nxstack and kern.elf64.nxstack (since FreeBSD 9.0).

You can use limits(1) to start a program with a different stack size, or use login.conf(5) to set the limits for different classes of users. The stack boundary looks hard-coded in the kernel. See the field sv_usrstack of the struct sysentvec for your architecture.

Edit Your program can request a larger maximum stack size by using setrlimit(2).

The GNU linker supports a --stack option, but according to the manual page;

This option is specific to the i386 PE targeted port of the linker

So this only works on windows.