Re: -Wl,-z,noexecstack hack removed for Linux and FreeBSD

Hi Stephan,

On 06/22/2010 03:57 PM, Stephan Bergmann wrote:
> On 06/22/10 15:19, Matthias Huetsch wrote:
>> Hmm, I'm not sure I understand why linking with "-z noexecstack" would
>> be a hack.
> 
> The entity providing the assembler-level input data for a link object
> (the C/C++ compiler in case of a C/C++ source file; the human author of
> an assembler source file; etc.) knows whether or not that object needs
> executable stack, and no other entity knows that (esp. not the linker).
>  The GCC C/C++ compiler in the old Hamburg tool chain, while being the
> entity that knew that the objects it produced did not require executable
> stack, failed to pass this information on to the linker.  In that sense,
> -Wl,-z,noexecstack was a hack to work around the shortcomings of that
> old compiler.

Okay, understood. Only, that in this case I am the human, that wants to
specify a non-executable stack for my application (but, see below).

>> To me it is an additional security measure, to explicitly mark an
>> executable to not require executable stack pages (and not rely on
>> possibly incesure defaults).
>>
>> So, I guess I would choose to keep linking with "-z noexecstack" (and in
>> fact think, every executable in the system should be linked that way).
> 
> In which case it would be better to use a system that forbids execution
> of objects that claim they require executable stack.  In such a system,
> erroneously overriding an object's requirement of executable stack via
> -z noexecstack leads to obscure failure during runtime, while it would
> otherwise have lead to a meaningful error message upon start up of that
> object.

Well, I think it is not so important what system a user chooses. The
point is, I want to provide an application, that is not vulnerable to
exploits making use of executable stack. I want non-executable stack,
always, on every system, not override-able by any component that gets
mapped into my processes address space.

I short, I want non-executable stack, and thus an explicit "-z
nonexecstack" for soffice.bin (an our other executables).

Matthias
> 
> -Stephan