Message-ID: <20171218055746.GC4627@eros>
Date:   Mon, 18 Dec 2017 16:57:46 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     kaiwan.billimoria@...il.com
Cc:     linux-kernel@...r.kernel.org,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] leaking_addresses: add generic 32-bit support

On Mon, Dec 18, 2017 at 09:24:47AM +0530, kaiwan.billimoria@...il.com wrote:
> The script attempts to detect the architecture it's running upon; as of now,
> we explicitly support x86_64, PPC64 and x86_32.
> If it's one of them, we proceed "normally". If we fail to detect the arch,
> we fallback to 64-bit scanning, unless the user has passed either of these
> option switches: "--32-bit" and/or "--page-offset-32bit=<val>".
> 
> If so, we switch to scanning for leaked addresses based on the value of
> PAGE_OFFSET (via an auto-detected or fallback mechanism).
> 
> As of now, we have code (or "rules") to detect special cases for x86_64 and ppc64
> (in the get_address_re sub). Also, we now have also builtin "stubs", for lack of a better term,
> where additional rules for other 64-bit arch's can be plugged in, in future,
> as applicable.
> 
> Signed-off-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
> ---
> 
> This is a patch based on Tobin's latest tree, 'leaks' branch. 
> Applies on top of commit 6c3942594657 (leaking_addresses: add support for 5 page table levels (origin/leaks))

That commit is not the tip of the branch. leaks branch is currently at

commit 266891c62bf0 (leaking_addresses: add support for 5 page table levels)

> 
> Thanks,
> Kaiwan.
> 
>  scripts/leaking_addresses.pl | 213 +++++++++++++++++++++++++++++++++++++------
>  1 file changed, 184 insertions(+), 29 deletions(-)
> 
> diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
> index a29e13e577a7..a667f243c95b 100755
> --- a/scripts/leaking_addresses.pl
> +++ b/scripts/leaking_addresses.pl
> @@ -1,10 +1,10 @@
>  #!/usr/bin/env perl
>  #
>  # (c) 2017 Tobin C. Harding <me@...in.cc>
> -
> +# (c) 2017 Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
>  # 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 kernel for potential leaking addresses.
>  #  - Scans dmesg output.
>  #  - Walks directory tree and parses each file (for each directory in @DIRS).
>  #
> @@ -35,7 +35,7 @@ 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;
> @@ -48,7 +48,9 @@ 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 $kernel_config_file = "";   # Kernel configuration file.
> +my $opt_32_bit = 0;            # Detect 32-bit kernel leaking addresses.
> +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',
> @@ -97,17 +99,19 @@ 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.
> -       --kernel-config-file=<file>     Kernel configuration file (e.g /boot/config)
> -       -d, --debug                     Display debugging output.
> -       -h, --help, --versionq          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.
> +       --32-bit                        Detect 32-bit kernel leaking addresses.
> +       --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.

We don't need this, it's already indented.

> -Scans the running (64 bit) kernel for potential leaking addresses.
> +Scans the running kernel for potential leaking addresses.
>  
>  EOM
>         exit($exitcode);
> @@ -123,7 +127,9 @@ GetOptions(
>         'squash-by-path'        => \$squash_by_path,
>         'squash-by-filename'    => \$squash_by_filename,
>         'raw'                   => \$raw,
> -       'kernel-config-file=s'  => \$kernel_config_file,
> +       '32-bit'                => \$opt_32_bit,
> +       'page-offset-32bit=o'   => \$page_offset_32bit,
> +       'kernel-config-file=s'  => \$kernel_config_file,

Perhaps

$opt_32bit so as to be consistent.

>  ) or help(1);
>  
>  help(0) if ($help);
> @@ -139,11 +145,16 @@ if (!$input_raw and ($squash_by_path or $squash_by_filename)) {
>         exit(128);
>  }
>  
> -if (!is_supported_architecture()) {
> -       printf "\nScript does not support your architecture, sorry.\n";
> -       printf "\nCurrently we support: \n\n";
> -       foreach(@SUPPORTED_ARCHITECTURES) {
> -               printf "\t%s\n", $_;
> +show_detected_architecture() if $debug;
> +
> +if (!is_known_architecture()) {
> +       printf STDERR "\n*** WARNING! Script does not recognize your architecture ***\n";
> +       if ($opt_32_bit or $page_offset_32bit) {
> +               printf STDERR "Scanning for 32-bit leaking kernel addresses\n\n";
> +       } else {
> +               printf STDERR "Scanning for 64-bit leaking kernel addresses\n";
> +               printf STDERR "If you\'d rather scan for 32-bit addresses, use the ";
> +               printf STDERR "--32-bit (and --page-offset-32bit=) option switch(es).\n\n";
>         }
>  
>         my $archname = $Config{archname};
> @@ -168,9 +179,14 @@ sub dprint
>         printf(STDERR @_) if $debug;
>  }
>  
> -sub is_supported_architecture
> +sub is_known_architecture
> +{
> +       return (is_64bit() or is_ix86_32());
> +}
> +
> +sub is_64bit
>  {
> -       return (is_x86_64() or is_ppc64());
> +       return (is_x86_64() or is_ppc64() or is_arm64() or is_mips64());
>  }

Perhaps we could have

sub is_32bit
{
	if ($opt_32bit or $page_offset_32bit) {
		return 1;
	}

	if (is_ix86_32()) {
		return 1;
	}
	return 0;
}

>  
>  sub is_x86_64
> @@ -193,6 +209,50 @@ sub is_ppc64
>         return 0;
>  }
>  
> +sub is_arm64
> +{
> +       if (`uname -m` eq "aarch64") {
> +               return 1;
> +       }
> +       return 0;
> +}
> +
> +sub is_mips64
> +{
> +       if (`uname -m` eq "mips64") {
> +               return 1;
> +       }
> +       return 0;
> +}
> +
> +sub is_ix86_32
> +{
> +       my $archname = $Config{archname};
> +
> +       if ($archname =~ m/i[3456]86-linux/) {
> +               return 1;
> +       }
> +       return 0;
> +}

Why do we use $Config{archname} here and `uname -m` above? Can we use
just one of them? If so we could have a helper function

sub is_arch()
{
	my ($desc) = @_;

	if (`uname -m` eq $desc) {
		return 1;
	}
	return 0;
}

and

is_mips64 { is_arch("mips64"); }
...

> +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";

We probably should use capitals for PPC64 since ARM and MIPS get capitals.

> +       } elsif (is_arm64()) {
> +               printf "ARM64\n";
> +       } elsif (is_mips64()) {
> +               printf "MIPS64\n";
> +       } else {
> +               printf "failed to detect architecture\n"
> +       }
> +}
> +
>  # gets config option value from kernel config file
>  sub get_kernel_config_option
>  {
> @@ -220,7 +280,8 @@ sub get_kernel_config_option
>         }
>  
>         foreach my $file (@config_files) {
> -               dprint("parsing config file: %s\n", $file);
> +               printf("file: %s\n", $file) if $debug;

We should actually just remove this debugging line all together, it will
be overly verbose and not that useful (see below).

>                 $value = option_from_file($option, $file);
>                 if ($value ne "") {
>                         last;
> @@ -258,6 +319,14 @@ sub is_false_positive
>  {
>         my ($match) = @_;
>  
> +       # 32 bit architectures, actual or forced
> +
> +       if (!is_64bit() and ($opt_32_bit or $page_offset_32bit)) {
> +               return is_false_positive_32bit($match);
> +       }

and now we could have just

	if (is_32_bit()) {
		...

> +
> +       # 64 bit architectures
> +
>         if ($match =~ '\b(0x)?(f|F){16}\b' or
>             $match =~ '\b(0x)?0{16}\b') {
>                 return 1;
> @@ -281,6 +350,91 @@ sub is_in_vsyscall_memory_region
>         return ($hex >= $region_min and $hex <= $region_max);
>  }
>  
> +sub is_false_positive_32bit
> +{
> +       my ($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);

Remember we don't like 'eval' :) Just make sure your code does not
generate warnings in the first place.

> +       if ($addr32 < $page_offset) {
> +               return 1;
> +       }
> +
> +       return 0;
> +}
> +
> +sub get_page_offset
> +{
> +       my $page_offset;
> +       my $default_offset = hex("0xc0000000");
> +       my @config_files;
> +
> +       # Allow --page-offset-32bit to override.
> +       if ($page_offset_32bit != 0) {
> +               return $page_offset_32bit;
> +       }

We don't need the rest of this function since we now have

	get_kernel_config_option('CONFIG_PAGE_OFFSET');

And using this for CONFIG_PAGE_OFFSET after we have done so for
CONFIG_PGTABLE_LEVELS is why I suggest above removing debugging line.

> +
> +       # Allow --kernel-config-file to override.
> +       if ($kernel_config_file ne "") {
> +               @config_files = ($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";
> +                       system("rm -f $tmp_file 2>/dev/null");
> +               } else {
> +                       $page_offset = parse_kernel_config_file($tmp_file);
> +                       system("rm -f $tmp_file");
> +                       if ($page_offset ne "") {
> +                               return hex($page_offset);
> +                       }
> +               }
> +       }
> +
> +       foreach my $config_file (@config_files) {
> +               chomp $config_file;
> +               $page_offset = parse_kernel_config_file($config_file);
> +               if ($page_offset ne "") {
> +                       return hex($page_offset);
> +               }
> +       }
> +
> +       printf STDERR "\nFailed to parse kernel config files\n";
> +       printf STDERR "*** NOTE ***\n";
> +       printf STDERR "Falling back to PAGE_OFFSET = %#x\n\n", $default_offset;
> +
> +       return $default_offset;
> +}
> +
> +sub parse_kernel_config_file
> +{
> +       my ($file) = @_;
> +       my $config = 'CONFIG_PAGE_OFFSET';
> +       my $str = "";
> +       my $val = "";
> +
> +       open(my $fh, "<", $file) or return "";
> +       while (my $line = <$fh> ) {
> +               if ($line =~ /^$config/) {
> +                       ($str, $val) = split /=/, $line;
> +                       chomp($val);
> +                       last;
> +               }
> +       }
> +
> +       close $fh;
> +       return $val;
> +}
> +
>  # True if argument potentially contains a kernel address.
>  sub may_leak_address
>  {
> @@ -300,7 +454,7 @@ sub may_leak_address
>         }
>  
>         $address_re = get_address_re();
> -       dprint("Kernel address regular expression: %s\n", $address_re);
> +#      dprint("Kernel address regular expression: %s\n", $address_re);

Just remove this line altogether (I assume it annoyed you while
debugging).

>         while (/($address_re)/g) {
>                 if (!is_false_positive($1)) {
> @@ -313,16 +467,17 @@ sub may_leak_address
>  
>  sub get_address_re
>  {
> -       my $re;
> +       my $re = "";
>  
>         if (is_x86_64()) {
>                 $re = get_x86_64_re();
>         } elsif (is_ppc64()) {
>                 $re = '\b(0x)?[89abcdef]00[[:xdigit:]]{13}\b';
	
	} elsif (is_32bit())
		$re = '\b(0x)?[[:xdigit:]]{8}\b';
> -       }
> -
> -       if ($re eq "") {
> -               print STDERR "$0: failed to build kernel address regular expression\n";

And then we can leave this as is.

> +       ###
> +       # Any special cases for other arch's go below this line
> +       ###
> +       } else {  # nothing? then we assume it's a generic 32-bit
> +               $re = '\b(0x)?[[:xdigit:]]{8}\b';
>         }
>  
>         return $re;
> -- 
> 2.14.3

thanks,
Tobin.

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