Message-ID: <20171128211003.GY17858@eros>
Date:   Wed, 29 Nov 2017 08:10:03 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Alexander Kapshuk <alexander.kapshuk@...il.com>
Cc:     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 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';

> 		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
		
		@config_files = ($tmpkconf)

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

 		open(my $fh, "<", $config_file) or next;

> 		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.

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