Message-ID: <CAJ1xhMXjSTV92DxRz269sB=fZLEXJimr7_8PX8viamm02+xN1w@mail.gmail.com>
Date:   Tue, 28 Nov 2017 15:16:24 +0200
From:   Alexander Kapshuk <alexander.kapshuk@...il.com>
To:     "Tobin C. Harding" <me@...in.cc>
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 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. Apologies for the absence
of indentation.
Disclaimer: I did not test-run the code being proposed.

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;
}

if (($page_offset = parse_kernel_config_file()) != "") {
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") {
if (system("gunzip < /proc/config.gz > /tmp/tmpkconf") == 0) {
push @config_files, "/tmp/tmpkconf";
}
}

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

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