selinux: generalize disabling of execmem for plt-in-heap archs

selinux: generalize disabling of execmem for plt-in-heap archs

On Tue, 2010-04-27 at 11:47 -0700, David Miller wrote:
> From: "Tom \"spot\" Callaway" <tcallawa@redhat.com>
> Date: Tue, 27 Apr 2010 14:20:21 -0400
>
> > [root@apollo ~]$ cat /proc/2174/maps
> > 00010000-00014000 r-xp 00000000 fd:00 15466577
> >  /sbin/mingetty
> > 00022000-00024000 rwxp 00002000 fd:00 15466577
> >  /sbin/mingetty
> > 00024000-00046000 rwxp 00000000 00:00 0
> >  [heap]
>
> SELINUX probably barfs on the executable heap, the PLT is in the HEAP
> just like powerpc32 and that's why VM_DATA_DEFAULT_FLAGS has to set
> both executable and writable.
>
> You also can't remove the CONFIG_PPC32 ifdefs in selinux, since
> because of the VM_DATA_DEFAULT_FLAGS setting used still in that arch,
> the heap will always have executable permission, just like sparc does.
> You have to support those binaries forever, whether you like it or not.
>
> Let's just replace the CONFIG_PPC32 ifdef in SELINUX with CONFIG_PPC32
> || CONFIG_SPARC as in Tom's original patch and let's be done with
> this.
>
> In fact I would go through all the arch/ header files and check the
> VM_DATA_DEFAULT_FLAGS settings and add the necessary new ifdefs to the
> SELINUX code so that other platforms don't have the pain of having to
> go through this process too.

To avoid maintaining per-arch ifdefs, it seems that we could just
directly use (VM_DATA_DEFAULT_FLAGS & VM_EXEC) as the basis for deciding
whether to enable or disable these checks.   VM_DATA_DEFAULT_FLAGS isn't
constant on some architectures but instead depends on
current->personality, but we want this applied uniformly.  So we'll just
use the initial task state to determine whether or not to enable these
checks.

Signed-off-by:  Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: James Morris <jmorris@namei.org>