Subject: Re: [kernel-hardening] [PATCH v4] scripts: add leaking_addresses.pl

From: "Tobin C. Harding" <[email-masked]>
Date: Mon, 13 Nov 2017 08:18:23 +1100

On Sun, Nov 12, 2017 at 10:02:55AM -0800, Frank Rowand wrote:
> Hi Michael,
> 
> On 11/12/17 03:49, Michael Ellerman wrote:
> > Hi Frank,
> > 
> > Frank Rowand <[email-masked]> writes:
> >> Hi Michael, Tobin,
> >>
> >> On 11/08/17 04:10, Michael Ellerman wrote:
> >>> "Tobin C. Harding" <[email-masked]> writes:
> >>>> 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.
> >>>
> >>> That doesn't work super well on other architectures :D
> >>>
> >>> I don't speak perl but presumably you can check the arch somehow and
> >>> customise the regex?
> >>>
> >>> ...
> >>>> +# Return _all_ non false positive addresses from $line.
> >>>> +sub extract_addresses
> >>>> +{
> >>>> +        my ($line) = @_;
> >>>> +        my $address = '\b(0x)?ffff[[:xdigit:]]{12}\b';
> >>>
> >>> On 64-bit powerpc (ppc64/ppc64le) we'd want:
> >>>
> >>> +        my $address = '\b(0x)?[89abcdef]00[[:xdigit:]]{13}\b';
> >>>
> >>>
> >>>> +# Do not parse these files (absolute path).
> >>>> +my @skip_parse_files_abs = ('/proc/kmsg',
> >>>> +			    '/proc/kcore',
> >>>> +			    '/proc/fs/ext4/sdb1/mb_groups',
> >>>> +			    '/proc/1/fd/3',
> >>>> +			    '/sys/kernel/debug/tracing/trace_pipe',
> >>>> +			    '/sys/kernel/security/apparmor/revision');
> >>>
> >>> Can you add:
> >>>
> >>>   /sys/firmware/devicetree
> >>>
> >>> and/or /proc/device-tree (which is a symlink to the above).
> >>
> >> /proc/device-tree is a symlink to /sys/firmware/devicetree/base
> > 
> > Oh yep, forgot about the base part.
> > 
> >> /sys/firmware contains
> >>    fdt              -- the flattened device tree that was passed to the
> >>                        kernel on boot
> >>    devicetree/base/ -- the data that is currently in the live device tree.
> >>                        This live device tree is represented as directories
> >>                        and files beneath base/
> >>
> >> The information in fdt is directly available in the kernel source tree
> > 
> > On ARM that might be true, but not on powerpc.

Looks like we should be considering architecture specific lists for
files/directories to skip.

thanks,
Tobin.