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SubjectRe: [kernel-hardening] [PATCH v4] scripts: add leaking_addresses.pl
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On Mon, 2017-11-13 at 09:21 +1100, Tobin C. Harding wrote:
> On Fri, Nov 10, 2017 at 07:26:34PM +0530, kaiwan.billimoria@gmail.com
> wrote:
> > On Tue, 2017-11-07 at 21:32 +1100, Tobin C. Harding wrote:
> > > Currently we are leaking addresses from the kernel to user space.
> > > This
> > > script is an attempt to find some of those leakages. Script
> > > parses
> > > `dmesg` output and /proc and /sys files for hex strings that look
> > > like
> > > kernel addresses.
> > >
> > > Only works for 64 bit kernels, the reason being that kernel
> > > addresses
> > > on 64 bit kernels have 'ffff' as the leading bit pattern making
> > > greping
> > > possible. On 32 kernels we don't have this luxury.
> >
> > Tobin C. Harding <me@tobin.cc> wrote:
> > > Only works for 64 bit kernels, the reason being that kernel
> > > addresses
> > > on 64 bit kernels have 'ffff' as the leading bit pattern making
> > > greping
> > > possible. On 32 kernels we don't have this luxury.
> >
> > [RFC] leaking_addresses.pl - enhance it to work for 32-bit kernels
> > as well
> >
> > (Firstly, apologies if I've got the protocol horribly wrong- should
> > this
> > be a new thread altogether?)
>
> I think this patch will need to wait until the patch set that is
> currently in flight is either merged or dropped.
>
Thanks for looking at it!
Okay; blocking on merge || drop... :-)

> >
> We can work this out pragmatically, Perl can give us an architecture
> string then a few regexs can ascertain which architecture we are
> running
> on. This is in the inflight patch set.
>
> > The patch below does Not take into account (yet) stuff like:
> > - exactly which files & dirs should be skipped on 32-bit (will it
> > be
> > identical to 64-bit?; unsure..)
>
> As per discussion later in this thread we may need to consider
> architecture specific lists for files/directories to skip.
Right
>
> > - it currently hard-codes a global 'PAGE_OFFSET_32BIT=0xc0000000'
> > , just
> > so I can test quickly; must figure whether to query it or pass it;
> > Suggestions?
>
> Perhaps we should have a command line option for this.
>
> --kernel-base-address

Why not just detect it programatically? We could devise a series of
fallbacks; something like:
- if .config exists in the kernel source tree root, grep it for
PAGE_OFFSET
- if not, grep the arch-specific (arch/<arch>/configs/<config-file>)
for the same
- if for some reason we don't have enough info regarding specific
platform and thus the defconfig filename (could happen for ARM, PPC?),
we then fail and request the user to pass it as a parameter.

> > - the 'false positives'; again, what differs for 32-bit?
> > (BTW, shouldn't the dmesg 'root=UUID=<...>' line be a false
> > positive
> > & skipped?).
>
> We could probably do with architecture specific false
> positives. Inflight patch set refactors false_positive() so adding to
> this should be easy.
Sure.
>
> > Also, I must point out that I'm a complete newbie to Perl :-) so,
> > pl excuse
> > my highly inadequate perl-foo; I rely on you perl gurus out there
> > to fix
> > and optimize :)
>
> I'm no Perl guru but following are a few tips I have picked up over
> the
> last month.
Thanks, will fix the issues you point out..
>
> >
> Conceptually your ideas look good to me. If there is some reason this
> approach won't work hopefully someone else will jump in and say so.
>
> Nice work, thanks for putting in effort to get 32 bit machines
> supported. Let's see what happens with the inflight patch set then
> work
> on getting these ideas in.
>
Thanks! yes..
> thanks,
> Tobin.

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