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SubjectRe: [kernel-hardening] [PATCH v4] scripts: add leaking_addresses.pl
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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?)

Ok so, I was interested in figuring - why not have this useful script work
for 32-bit kernel virtual addresses as well (and those systems by
extension).

The approach am considering, pl correct me if I'm way off:
on 32-bit, the kernel macro PAGE_OFFSET will give us the user-kernel split;
(alternatively, could also script up CONFIG_VMSPLIT_[n]G and figure the
split from there.)

For the time being, lets say we go with the "use PAGE_OFFSET" approach and
PAGE_OFFSET = 0xc0000000 , whch implies we have a 3:1 GB user:kernel split.
So any virtual addresses >= PAGE_OFFSET are kernel virtual addresses (i
know, untrue on some ARM-32 systems!).

As a very early and *far-from-perfect* start, I've enhanced Tobin's Perl
script to take into account 32-bit address space by passing the
parameter '--bit-size='.

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..)
- 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?
- the 'false positives'; again, what differs for 32-bit?
(BTW, shouldn't the dmesg 'root=UUID=<...>' line be a false positive
& skipped?).

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 :)

Yes, I've **Very Minimally** tested the patch in it's current form on:
a) a regular (Fedora 26) x86_64 desktop,
b) a (Debian 7) 32-bit kernel (VM) with PAGE_OFFSET=3 Gb
and it seems all right, considering...

Some sample output from test (b), if interested:
=====
dmesg: [ 0.000000] found SMP MP-table at [c00f1280] f1280
dmesg: [ 0.000000] Base memory trampoline at [c009b000] 9b000 size 16384
dmesg: [ 0.000000] ACPI: Local APIC address 0xfee00000
dmesg: [ 0.000000] free_area_init_node: node 0, pgdat c1418bc0, node_mem_map dfbfa200
dmesg: [ 0.000000] ACPI: Local APIC address 0xfee00000
dmesg: [ 0.000000] ACPI: IOAPIC (id[0x00] address[0xfec00000] gsi_base[0])
dmesg: [ 0.000000] IOAPIC[0]: apic_id 0, version 17, address 0xfec00000, GSI 0-23
dmesg: [ 0.000000] PERCPU: Embedded 14 pages/cpu @dfbe8000 s33344 r0 d24000 u57344
dmesg: [ 0.000000] fixmap : 0xffd36000 - 0xfffff000 (2852 kB)
dmesg: [ 0.000000] pkmap : 0xffa00000 - 0xffc00000 (2048 kB)
dmesg: [ 0.000000] vmalloc : 0xe07fb000 - 0xff9fe000 ( 498 MB)
dmesg: [ 0.000000] lowmem : 0xc0000000 - 0xdfffb000 ( 511 MB)
dmesg: [ 0.000000] .init : 0xc1421000 - 0xc148c000 ( 428 kB)

[...]

/proc/kallsyms: c10010e8 T _stext
/proc/kallsyms: c1002000 T hypercall_page
/proc/kallsyms: c1003000 t arch_local_save_flags
/proc/kallsyms: c1003007 t arch_local_irq_enable
/proc/kallsyms: c100300e T do_one_initcall

<< ... plenty more kallsyms of course (92.5% of the output to be precise!) ... >>

/proc/modules: loop 17803 0 - Live 0xe097c000
/proc/modules: crc32c_intel 12659 0 - Live 0xe096e000
/proc/modules: snd_pcm 53461 0 - Live 0xe09f5000
/proc/modules: snd_page_alloc 12867 1 snd_pcm, Live 0xe0957000
/proc/modules: snd_timer 22401 1 snd_pcm, Live 0xe093c000

[...]

/proc/modules: usb_common 12338 1 usbcore, Live 0xe0860000
/proc/timer_list: .base: dfbeb8b0
/proc/timer_list: #0: <dfbeb954>, tick_sched_timer, S:01, hrtimer_start_range_ns, swapper/0/0

[...]

/proc/iomem: f8000000-fbffffff : 0000:00:02.0
/proc/iomem: fc000000-fcffffff : 0000:00:02.0
/proc/iomem: fd000000-fd03ffff : 0000:00:03.0

[...]

/proc/11422/syscall: 7 0xffffffff 0xbf814618 0xa 0xa 0x0 0x1 0xbf8145b8 0xb7780428
/proc/11422/stack: [<c102953f>] kmap_atomic_prot+0x2f/0xe0
/proc/11422/stack: [<c1125213>] security_task_wait+0xc/0xd

[...]

/proc/bus/input/devices: B: KEY=4 2000000 3803078 f800d001 feffffdf ffefffff ffffffff fffffffe
/proc/1/net/ipv6_route: 00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 0000000f 00200200 lo

[...]

/proc/2/net/unix: dce872c0: 00000005 00000000 00000000 0002 01 4978 /dev/log
/proc/2/net/unix: dce87a40: 00000002 00000000 00010000 0001 01 5006 /var/run/acpid.socket
/proc/2/net/unix: dce87540: 00000002 00000000 00010000 0005 01 3246 /run/udev/control

[...]
=====
etc etc.


Finally, unsure if am working against the latest ver of your script Tobin, apologies if not.

Signed-off-by: Kaiwan N Billimoria <kaiwan@kaiwantech.com>
---

diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
index 2977371b2956..b6280dca8c46 100755
--- a/scripts/leaking_addresses.pl
+++ b/scripts/leaking_addresses.pl
@@ -45,6 +45,7 @@ my $P = $0;
my $V = '0.01';

# Directories to scan.
+#my @DIRS = ('/home/kai/0tmp/addr32_pl');
my @DIRS = ('/proc', '/sys');

# Command line options.
@@ -52,6 +53,7 @@ my $help = 0;
my $debug = 0;
my @dont_walk = ();
my @dont_parse = ();
+my $bit_size = 64;

# Do not parse these files (absolute path).
my @skip_parse_files_abs = ('/proc/kmsg',
@@ -86,6 +88,8 @@ my @skip_walk_dirs_any = ('self',
'stdin',
'stdout');

+my $PAGE_OFFSET_32BIT = 0xc0000000;
+
sub help
{
my ($exitcode) = @_;
@@ -96,10 +100,12 @@ Version: $V

Options:

+ --bit-size= 32|[64] Checks for 64-bit kernel addresses by default;
+ change to check for 32-bit kernel addresses by passing 32 here
--dont-walk=<dir> Don't walk tree starting at <dir>.
--dont-parse=<file> Don't parse <file>.
- -d, --debug Display debugging output.
- -h, --help, --version Display this help and exit.
+ -d, --debug Display debugging output.
+ -h, --help, --version Display this help and exit.

If an absolute path is passed to --dont_XXX then this path is skipped. If a
single filename is passed then this file/directory will be skipped when
@@ -117,8 +123,9 @@ EOM
}

GetOptions(
- 'dont-walk=s' => \@dont_walk,
- 'dont-parse=s' => \@dont_parse,
+ 'dont-walk=s' => \@dont_walk,
+ 'dont-parse=s' => \@dont_parse,
+ 'bit-size=i' => \$bit_size,
'd|debug' => \$debug,
'h|help' => \$help,
'version' => \$help
@@ -126,6 +133,10 @@ GetOptions(

help(0) if ($help);

+if ($bit_size != 64 && $bit_size != 32) {
+ help(1);
+}
+
push_to_global();

parse_dmesg();
@@ -168,6 +179,7 @@ sub push_to_global
push_in_abs_any(\@dont_parse, \@skip_parse_files_abs, \@skip_parse_files_any);
}

+# NOT updated for 32-bit kernel addresses yet
sub is_false_positive
{
my ($match) = @_;
@@ -183,6 +195,7 @@ sub is_false_positive
return 1;
}

+# TODO - skip the 'root=UUID=<...>' line as well
return 0;
}

@@ -190,7 +203,8 @@ sub is_false_positive
sub may_leak_address
{
my ($line) = @_;
- my $address = '\b(0x)?ffff[[:xdigit:]]{12}\b';
+ my $address64 = '\b(0x)?ffff[[:xdigit:]]{12}\b';
+ my $address32 = '\b(0x)?[[:xdigit:]]{8}\b';

# Signal masks.
if ($line =~ '^SigBlk:' or
@@ -202,11 +216,23 @@ sub may_leak_address
$line =~ '\b[[:xdigit:]]{14} [[:xdigit:]]{16} [[:xdigit:]]{16}\b') {
return 0;
}
-
- while (/($address)/g) {
+
+ if ($bit_size == 64) {
+ while (/($address64)/g) {
if (!is_false_positive($1)) {
return 1;
}
+ }
+ } elsif ($bit_size == 32) {
+ while (/($address32)/g) {
+ my $addr32 = eval hex($1);
+ if ($addr32 < $PAGE_OFFSET_32BIT) {
+ return 0;
+ }
+ if (!is_false_positive($addr32)) {
+ return 1;
+ }
+ }
}

return 0;

scripts/leaking_addresses.pl | 40 +++++++++++++++++++++++++++++++++-------
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