Re: [gentoo-hardened] some pax questions

On 21 Nov 2007 at 12:49, Brian Kroth wrote:

> Still sifting through the docs, so I apologize if these are answered elsewhere.
>
> - In the docs for ASLR it notes that a side effect is memory space
>   fragmentation.  How is this dealt with, if at all?  Perhaps this isn't as big
>   a problem as I think it is.

uhm, what is there to deal with? ;-) you either want randomization or
you don't... the side effect is what the doc says, the unmapped region
sizes between the main areas are not fixed but change, i.e., they can
be bigger or smaller than what a non-ASLR kernel creates. whether that
helps a given app or not depends on the app of course.

> - In the pspax output, under MAPS, is w^x meant to indicate that the process has
>   writable AND executable maps, or that it has writable but NOT executable maps?

it means the app doesn't have writable AND executable mappings.

>   I presume the other output, w|x, (which I don't seem to have any of) is an OR,
>   meaning the process has maps that have both bits set, correct?

correct (you can 'grep rwx /proc/pid/maps' to see them).

> and ASLR would use RANDEXEC on ET_EXEC binaries,

RANDEXEC (when it existed) was never enabled by default.

>   rather than RANDMMAP, but everything else should still work - correct?

the only difference is that ET_EXEC executables won't be randomized.

>  Will the other two memory areas still be randomized where applicable?

yes, RANDEXEC was an independent feature within ASLR. in fact, not only
the stack/mmap regions will continue to be randomized but the brk based
heap as well (albeit with less entropy by virtue of lacking the random
bits that would come from the main executable base).

>  Do I need to just add RANDEXEC manually to my .config or is there some
> special combo that hides it?

no, i removed it from PaX some time ago as it became too hard to maintain
in 2.6 for little if any gain.

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