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Date:   Wed, 29 Nov 2017 21:16:40 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Alexander Kapshuk <alexander.kapshuk@...il.com>
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 Wed, Nov 29, 2017 at 09:59:59AM +0200, Alexander Kapshuk wrote:
> 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.

I'm a stickler for no const strings or magic numbers but it's Kaiwan's
patch, if he puts it in with const strings I'll apply it as is :)

> >
> >>               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.

You are correct, since the beginning of this function that has been the
algorithm. My observation is that if /proc/config.gz is present then we
don't need to parse the other files so it is better to blow them away.

I don't know enough about the whole Linux-sphere to know if this is
correct. But it seems reasonable that even if there is more than one way
to look at the running kernels config file they will all be the same,
the system would be pretty broken if they were different.

So once we have found a readable config file just parse it and be done
with it, no need to loop over any others.

thanks,
Tobin.

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