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The execstack program can be used to mark ELF-binaries as needing an executable stack.

Is there a similar way to mark the heap as executable? Preferably for a single binary but if that's not possible, a system-wide solution would be useful too.

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Setting an executable stack (or setting a non-executable stack) made no difference on any version of Linux I tried it on (2.6.9 on x86_64, 2.4.21 on x86_64, 2.6.20.9 x86, 3.1.4 x86). I don't have access to Solaris or *BSD machines at the moment. I'm guessing that the kernels in question aren't compiled to disallow execution of code "on the stack". See this wikipedia article, which says either a patch or a compile option is necessary.

I have written a C program that runs in malloc-ed memory. It works on all the same kernels and architecutres I mentioned above. I doubt you will find a specific tool like execstack to mark an executable file as "heap executable". About the best I could tell you is that you'll have to use the mprotect() system call. Even using mprotect() I think that you'll find some of the more unusual architectures out there (the old DEC Alpha, or HP's "Precision Architecture") just won't ever allow executing out of the heap.

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I don't think the old architectures would behave that way, the underlying hardware has no way of knowing what memory pages are mmap'ed executable files and which are meant for heap space, unless it is told. Architectures that don't support something like the no-execute flag on pages will always have executable heap, for others, the kernel is the only limitation. –  wingedsubmariner Nov 27 '13 at 20:50

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