Re: How to make stack executable on demand?

[Arjan van de Ven]

On Fri, Apr 16, 2004 at 01:46:51PM -0700, H. J. Lu wrote:
> On Fri, Apr 16, 2004 at 10:02:58PM +0200, Arjan van de Ven wrote:
> > >  But it will either fail if
> > > kernel is set with non-executable stack,
> > 
> > eh no. mprotect with prot_exec is still supposed to work. The stacks
> > still have MAY_EXEC attribute, just not the actual EXEC attribute
> 
> Ok. It looks like a bug in Red Hat EL 3 kernel. In fs/exec.c, there
> are
> 
>                 if (executable_stack)
>                         mpnt->vm_flags = VM_STACK_FLAGS | VM_MAYEXEC | VM_EXEC;
> 		else
>                         mpnt->vm_flags = VM_STACK_FLAGS & ~(VM_MAYEXEC|VM_EXEC); 

yep that's a bug


> The VM_MAYEXEC bit is untouched. Now the question is if it is a good
> idea for user to change stack permission.

it's required for correct operation and "security wise" it doesn't matter,
if someone can execute an mprotect syscall the game is over anyway

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