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Date: Wed, 29 Nov 2017 09:59:59 +0200
From: Alexander Kapshuk <alexander.kapshuk@...il.com>
To: "Tobin C. Harding" <me@...in.cc>
Cc: Kaiwan Billimoria <kaiwan.billimoria@...il.com>, 
	linux-kernel <linux-kernel@...r.kernel.org>, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] leaking_addresses: add support for 32-bit kernel addresses

On Tue, Nov 28, 2017 at 11:10 PM, Tobin C. Harding <me@...in.cc> wrote:
> On Tue, Nov 28, 2017 at 03:16:24PM +0200, Alexander Kapshuk wrote:
>> On Tue, Nov 28, 2017 at 8:32 AM, Tobin C. Harding <me@...in.cc> wrote:
>> > Currently, leaking_addresses.pl only supports scanning 64 bit
>> > architectures. This is due to how the regular expressions are formed. We
>> > can do better than this. 32 architectures can be supported if we take
>> > into consideration the kernel virtual address split.
>> >
>> > Add support for ix86 32 bit architectures.
>> >  - Add command line option for page offset.
>> >  - Add command line option for kernel configuration file.
>> >  - Parse kernel config file for page offset (CONFIG_PAGE_OFFSET).
>> >  - Use page offset when checking for kernel virtual addresses.
>> >
>> > Signed-off-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
>> > Signed-off-by: Tobin C. Harding <me@...in.cc>
>> > ---
>> >
>> > As discussed this is a patch based on Kaiwan's previous patch. This
>> > patch represents co development by Kaiwan and Tobin.
>> >
>> > Applies on top of commit 4fbd8d194f06 (Linux 4.15-rc1)
>> >
>> > thanks,
>> > Tobin.
>> >
>> >  scripts/leaking_addresses.pl | 168 +++++++++++++++++++++++++++++++++++++------
>> >  1 file changed, 148 insertions(+), 20 deletions(-)
>> >
>> > diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
>> > index bc5788000018..f03f2f140e0a 100755
>> > --- a/scripts/leaking_addresses.pl
>> > +++ b/scripts/leaking_addresses.pl
>> > @@ -1,9 +1,11 @@
>> >  #!/usr/bin/env perl
>> >  #
>> >  # (c) 2017 Tobin C. Harding <me@...in.cc>
>> > +# (c) 2017 Kaiwan N Billimoria <kaiwan.billimoria@...il.com> (ix86 stuff)
>> > +#
>> >  # Licensed under the terms of the GNU GPL License version 2
>> >  #
>> > -# leaking_addresses.pl: Scan 64 bit kernel for potential leaking addresses.
>> > +# leaking_addresses.pl: Scan the kernel for potential leaking addresses.
>> >  #  - Scans dmesg output.
>> >  #  - Walks directory tree and parses each file (for each directory in @DIRS).
>> >  #
>> > @@ -22,6 +24,7 @@ use Cwd 'abs_path';
>> >  use Term::ANSIColor qw(:constants);
>> >  use Getopt::Long qw(:config no_auto_abbrev);
>> >  use Config;
>> > +use feature 'state';
>> >
>> >  my $P = $0;
>> >  my $V = '0.01';
>> > @@ -35,18 +38,19 @@ my $TIMEOUT = 10;
>> >  # Script can only grep for kernel addresses on the following architectures. If
>> >  # your architecture is not listed here and has a grep'able kernel address please
>> >  # consider submitting a patch.
>> > -my @SUPPORTED_ARCHITECTURES = ('x86_64', 'ppc64');
>> > +my @SUPPORTED_ARCHITECTURES = ('x86_64', 'ppc64', 'i[3456]86');
>> >
>> >  # Command line options.
>> >  my $help = 0;
>> >  my $debug = 0;
>> > -my $raw = 0;
>> > -my $output_raw = "";   # Write raw results to file.
>> > -my $input_raw = "";    # Read raw results from file instead of scanning.
>> > -
>> > +my $raw = 0;                   # Show raw output.
>> > +my $output_raw = "";           # Write raw results to file.
>> > +my $input_raw = "";            # Read raw results from file instead of scanning.
>> >  my $suppress_dmesg = 0;                # Don't show dmesg in output.
>> >  my $squash_by_path = 0;                # Summary report grouped by absolute path.
>> >  my $squash_by_filename = 0;    # Summary report grouped by filename.
>> > +my $page_offset_32bit = 0;     # 32-bit: value of CONFIG_PAGE_OFFSET
>> > +my $kernel_config_file = "";   # Kernel configuration file.
>> >
>> >  # Do not parse these files (absolute path).
>> >  my @skip_parse_files_abs = ('/proc/kmsg',
>> > @@ -95,14 +99,16 @@ Version: $V
>> >
>> >  Options:
>> >
>> > -       -o, --output-raw=<file>  Save results for future processing.
>> > -       -i, --input-raw=<file>   Read results from file instead of scanning.
>> > -           --raw                Show raw results (default).
>> > -           --suppress-dmesg     Do not show dmesg results.
>> > -           --squash-by-path     Show one result per unique path.
>> > -           --squash-by-filename Show one result per unique filename.
>> > -       -d, --debug              Display debugging output.
>> > -       -h, --help, --version    Display this help and exit.
>> > +       -o, --output-raw=<file>         Save results for future processing.
>> > +       -i, --input-raw=<file>          Read results from file instead of scanning.
>> > +             --raw                       Show raw results (default).
>> > +             --suppress-dmesg            Do not show dmesg results.
>> > +             --squash-by-path            Show one result per unique path.
>> > +             --squash-by-filename        Show one result per unique filename.
>> > +           --page-offset-32bit=<hex>   PAGE_OFFSET value (for 32-bit kernels).
>> > +           --kernel-config-file=<file> Kernel configuration file (e.g /boot/config)
>> > +       -d, --debug                     Display debugging output.
>> > +       -h, --help, --version           Display this help and exit.
>> >
>> >  Examples:
>> >
>> > @@ -115,7 +121,10 @@ Examples:
>> >         # View summary report.
>> >         $0 --input-raw scan.out --squash-by-filename
>> >
>> > -Scans the running (64 bit) kernel for potential leaking addresses.
>> > +       # Scan kernel on a 32-bit system with a 2GB:2GB virtual address split.
>> > +       $0 --page-offset-32bit=0x80000000
>> > +
>> > +Scans the running kernel for potential leaking addresses.
>> >
>> >  EOM
>> >         exit($exitcode);
>> > @@ -131,6 +140,8 @@ GetOptions(
>> >         'squash-by-path'        => \$squash_by_path,
>> >         'squash-by-filename'    => \$squash_by_filename,
>> >         'raw'                   => \$raw,
>> > +       'page-offset-32bit=o'   => \$page_offset_32bit,
>> > +       'kernel-config-file=s'  => \$kernel_config_file,
>> >  ) or help(1);
>> >
>> >  help(0) if ($help);
>> > @@ -146,7 +157,9 @@ if (!$input_raw and ($squash_by_path or $squash_by_filename)) {
>> >         exit(128);
>> >  }
>> >
>> > -if (!is_supported_architecture()) {
>> > +if (is_supported_architecture()) {
>> > +       show_detected_architecture() if $debug;
>> > +} else {
>> >         printf "\nScript does not support your architecture, sorry.\n";
>> >         printf "\nCurrently we support: \n\n";
>> >         foreach(@SUPPORTED_ARCHITECTURES) {
>> > @@ -177,7 +190,7 @@ sub dprint
>> >
>> >  sub is_supported_architecture
>> >  {
>> > -       return (is_x86_64() or is_ppc64());
>> > +       return (is_x86_64() or is_ppc64() or is_ix86_32());
>> >  }
>> >
>> >  sub is_x86_64
>> > @@ -200,10 +213,40 @@ sub is_ppc64
>> >         return 0;
>> >  }
>> >
>> > +sub is_ix86_32
>> > +{
>> > +       my $archname = $Config{archname};
>> > +
>> > +       if ($archname =~ m/i[3456]86-linux/) {
>> > +               return 1;
>> > +       }
>> > +       return 0;
>> > +}
>> > +
>> > +sub show_detected_architecture
>> > +{
>> > +       printf "Detected architecture: ";
>> > +       if (is_ix86_32()) {
>> > +               printf "32 bit x86\n";
>> > +       } elsif (is_x86_64()) {
>> > +               printf "x86_64\n";
>> > +       } elsif (is_ppc64()) {
>> > +               printf "ppc64\n";
>> > +       } else {
>> > +               printf "failed to detect architecture\n"
>> > +       }
>> > +}
>> > +
>> >  sub is_false_positive
>> >  {
>> >         my ($match) = @_;
>> >
>> > +       if (is_ix86_32()) {
>> > +               return is_false_positive_ix86_32($match);
>> > +       }
>> > +
>> > +       # 64 bit architectures
>> > +
>> >         if ($match =~ '\b(0x)?(f|F){16}\b' or
>> >             $match =~ '\b(0x)?0{16}\b') {
>> >                 return 1;
>> > @@ -220,6 +263,87 @@ sub is_false_positive
>> >         return 0;
>> >  }
>> >
>> > +sub is_false_positive_ix86_32
>> > +{
>> > +       my ($match) = @_;
>> > +       state $page_offset = get_page_offset(); # only gets called once
>> > +
>> > +       if ($match =~ '\b(0x)?(f|F){8}\b') {
>> > +               return 1;
>> > +       }
>> > +
>> > +       my $addr32 = eval hex($match);
>> > +       if ($addr32 < $page_offset) {
>> > +               return 1;
>> > +       }
>> > +
>> > +       return 0;
>> > +}
>> > +
>>
>>
>>
>> > +sub get_page_offset
>> > +{
>> > +       my $page_offset;
>> > +       my $default_offset = "0xc0000000";
>> > +       my @config_files;
>> > +
>> > +       # Allow --page-offset-32bit to over ride.
>> > +       if ($page_offset_32bit != 0) {
>> > +               return $page_offset_32bit;
>> > +       }
>> > +
>> > +       # Allow --kernel-config-file to over ride.
>> > +       if ($kernel_config_file != "") {
>> > +               @config_files = ($kernel_config_file);
>> > +       } else {
>> > +               my $config_file = '/boot/config-' . `uname -r`;
>> > +               @config_files = ($config_file, '/boot/config');
>> > +       }
>> > +
>> > +       if (-R "/proc/config.gz") {
>> > +               my $tmp_file = "/tmp/tmpkconf";
>> > +               if (system("gunzip < /proc/config.gz > $tmp_file")) {
>> > +                       dprint " parse_kernel_config: system(gunzip...) failed\n";
>> > +               } else {
>> > +                       $page_offset = parse_kernel_config_file($tmp_file);
>> > +                       if ($page_offset ne "") {
>> > +                               return $page_offset;
>> > +                       }
>> > +               }
>> > +               system("rm -f $tmp_file");
>> > +       }
>> > +
>> > +       foreach my $config_file (@config_files) {
>> > +               $page_offset = parse_kernel_config($config_file);
>> > +               if ($page_offset ne "") {
>> > +                       return $page_offset;
>> > +               }
>> > +       }
>> > +
>> > +       printf STDERR "Failed to parse kernel config files\n";
>> > +       printf STDERR "Falling back to %s\n", $default_offset;
>> > +       return $default_offset;
>> > +}
>> > +
>> > +sub parse_kernel_config_file
>> > +{
>> > +       my ($file) = @_;
>> > +       my $config = 'CONFIG_PAGE_OFFSET';
>> > +       my $val = "";
>> > +
>> > +       open(my $fh, "<", $file) or return "";
>> > +       while (my $line = <$fh> ) {
>> > +               if ($line =~ /^$config/) {
>> > +                       my ($str, $val) = split /=/, $line;
>> > +                       chomp($val);
>> > +                       last;
>> > +               }
>> > +       }
>> > +
>> > +       close $fh;
>> > +       return $val;
>> > +}
>> > +
>> > +
>>
>> Get_page_offset attempts to build a list of config files, which are
>> then passed into the parsing function for further processing.
>> This splits up the code to do with the config files between
>> get_page_offset() and parse_kernel_config_file().
>> May I suggest putting the kernel config file processing code into the
>> parse_kernel_config_file() instead, and let the parsing function
>> handle the config files and either return the page_offset or an empty
>> string.
>>
>> See below for the proposed implementation.
>
> Nice, this is much better! Thanks.
>
>> Apologies for the absence of indentation.
>
> Re-posting with indentation, comments in line.
>
>> Disclaimer: I did not test-run the code being proposed.
>
> I also did not test my comments ;)
>
>> sub get_page_offset
>> {
>>       my $default_offset = "0xc0000000";
>>       my $page_offset;
>>
>>       # Allow --page-offset-32bit to over ride.
>>       if ($page_offset_32bit != 0) {
>>               return $page_offset_32bit;
>>       }
>>
>>       $page_offset = parse_kernel_config_file();
>>       if ($page_offset ne "") {
>>               return $page_offset
>>       }
>>
>>       printf STDERR "Failed to parse kernel config files\n";
>>       printf STDERR "Falling back to %s\n", $default_offset;
>>
>>       return $default_offset;
>> }
>>
>> sub parse_kernel_config_file
>> {
>>       my @config_files;
>>       my $config = 'CONFIG_PAGE_OFFSET';
>>
>>       # Allow --kernel-config-file to over ride.
>>       if ($kernel_config_file != "") {
>>               @config_files = ($kernel_config_file);
>>       } else {
>>               my $config_file = '/boot/config-' . `uname -r`;
>>               @config_files = ($config_file, '/boot/config');
>>       }
>>
>>       if (-R "/proc/config.gz") {
>
> perhaps
>                 my $tmpkconf = '/tmp/tmpkconf';

my $tmpkconf is almost as long as /tmp/tmpkconf. The name of the tmp
file is self explanatory.
Using a variable instead of the filename in this particular context is
a matter of personal preference. If you prefer to use the variable
here, it's your call.

>
>>               if (system("gunzip < /proc/config.gz > /tmp/tmpkconf") == 0) {
>>                       push @config_files, "/tmp/tmpkconf";
>>               }
>>       }
>
> Won't there only ever be a single config file? So if /proc/config.gz is
> readable we could do

The code above builds a list of config files.
Assigning to @config_files as shown below would wipe out the config
files appended to the list so far, would it not?
So $tmpkconf needs appending to the list.

>
>                 @config_files = ($tmpkconf)
>
>>       foreach my $config_file (@config_files) {
>>               open(my $fh, "<", $config_file) or return "";
>
>                 open(my $fh, "<", $config_file) or next;

Good catch. If there's more config files to process we don't want to
return, but process the next one.

>
>>               while (my $line = <$fh> ) {
>>                       if ($line =~ /^$config/) {
>>                               my ($config_name, $page_offset) = split /=/, $line;
>>                               chomp($page_offset);
>>                               last;
>>                       }
>>               }
>>       }
>>       system("rm -f $tmp_file");
>>       close $fh;
>>
>>       return $page_offset;
>> }
>
> thanks,
> Tobin.

Thanks.

Alexander Kapshuk.

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