Re: [PATCH] leaking_addresses: add 32-bit support

[kaiwan . billimoria]

Hi Tobin,

On Mon, 2018-01-29 at 15:51 +1100, Tobin C. Harding wrote:
> Currently script only supports x86_64 and ppc64.  It would be nice to be
> able to scan 32-bit machines also.  We can add support for
> 32-bit architectures by modifying how we check for false positives,
> taking advantage of the page offset used by the kernel, and using the
> correct regular expression.
> 
> Support for 32-bit machines is enabled by the observation the kernel
> addresses on 32-bit machines are larger than the page offset.  We can
> use this to filter false positives when scanning the kernel for leaking
> addresses.
> 
> Programmatic determination of the running architecture is not
> immediately obvious.  We therefore provide a flag to enable scanning of
> 32-bit kernels.  Also we can check the kernel config file for the offset
> and if not found default to 0xc0000000.  A command line option to parse
> in the page offset is also provided.  We do automatically detect
> architecture if running on ix86.
> 
> Add support for 32-bit kernels.  Add a command line option for page
> offset.
> 
> Suggested-by: Kaiwan N Billimoria <kaiwan.billimoria@xxxxxxxxx>
> Signed-off-by: Tobin C. Harding <me@xxxxxxxx>
> ---
> 
> The basis for this patch has been in development for a while by Kaiwan
> but didn't get finished before the merge window opened.  I'd like to
> fast track this and get it to Linus this merge window (considering
> Spectre/Meltdown).  I have finished this work off and added the
> Suggested-by tag.  Kaiwan I hope you are not upset by this, extra
> ordinary circumstances seemed to require this action.
Definitely not; I understand and am glad you're on it a 100%. Apologies
that I couldn't work on this right now.. will try and keep track too.

Thanks,
Kaiwan.
> 
> thanks,
> Tobin.
> 
>  scripts/leaking_addresses.pl | 84 ++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 78 insertions(+), 6 deletions(-)
> 
> diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
> index 64a3cfa1175b..c13eb53d1c5a 100755
> --- a/scripts/leaking_addresses.pl
> +++ b/scripts/leaking_addresses.pl
> @@ -34,7 +34,7 @@ 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', 'x86');
>  
>  # Command line options.
>  my $help = 0;
> @@ -46,6 +46,8 @@ 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_32bit = 0;		# Scan 32-bit kernel.
> +my $page_offset_32bit = 0;	# Page offset for 32-bit kernel.
>  
>  # Do not parse these files (absolute path).
>  my @skip_parse_files_abs = ('/proc/kmsg',
> @@ -103,6 +105,8 @@ Options:
>  	      --squash-by-path		Show one result per unique path.
>  	      --squash-by-filename	Show one result per unique filename.
>  	--kernel-config-file=<file>     Kernel configuration file (e.g /boot/config)
> +	--32-bit			Scan 32-bit kernel.
> +	--page-offset-32-bit=o		Page offset (for 32-bit kernel 0xABCD1234).
>  	-d, --debug			Display debugging output.
>  	-h, --help, --versionq		Display this help and exit.
>  
> @@ -123,6 +127,8 @@ GetOptions(
>  	'squash-by-filename'    => \$squash_by_filename,
>  	'raw'                   => \$raw,
>  	'kernel-config-file=s'	=> \$kernel_config_file,
> +	'32-bit'		=> \$opt_32bit,
> +	'page-offset-32-bit=o'	=> \$page_offset_32bit,
>  ) or help(1);
>  
>  help(0) if ($help);
> @@ -138,7 +144,7 @@ if (!$input_raw and ($squash_by_path or $squash_by_filename)) {
>  	exit(128);
>  }
>  
> -if (!is_supported_architecture()) {
> +if (!(is_supported_architecture() or $opt_32bit or $page_offset_32bit)) {
>  	printf "\nScript does not support your architecture, sorry.\n";
>  	printf "\nCurrently we support: \n\n";
>  	foreach(@SUPPORTED_ARCHITECTURES) {
> @@ -146,6 +152,9 @@ if (!is_supported_architecture()) {
>  	}
>  	printf("\n");
>  
> +	printf("If you are running a 32-bit architecture you may use:\n");
> +	printf("\n\t--32-bit or --page-offset-32-bit=<page offset>\n\n");
> +
>  	my $archname = `uname -m`;
>  	printf("Machine hardware name (`uname -m`): %s\n", $archname);
>  
> @@ -169,7 +178,28 @@ sub dprint
>  
>  sub is_supported_architecture
>  {
> -	return (is_x86_64() or is_ppc64());
> +	return (is_x86_64() or is_ppc64() or is_ix86_32());
> +}
> +
> +sub is_32bit
> +{
> +	# Allow --32-bit or --page-offset-32-bit to override
> +	if ($opt_32bit or $page_offset_32bit) {
> +		return 1;
> +	}
> +
> +	return is_ix86_32();
> +}
> +
> +sub is_ix86_32
> +{
> +       my $arch = `uname -m`;
> +
> +       chomp $arch;
> +       if ($arch =~ m/i[3456]86/) {
> +               return 1;
> +       }
> +       return 0;
>  }
>  
>  sub is_arch
> @@ -261,6 +291,12 @@ sub is_false_positive
>  {
>  	my ($match) = @_;
>  
> +	if (is_32bit()) {
> +		return is_false_positive_32bit($match);
> +	}
> +
> +	# 64 bit false positives.
> +
>  	if ($match =~ '\b(0x)?(f|F){16}\b' or
>  	    $match =~ '\b(0x)?0{16}\b') {
>  		return 1;
> @@ -273,6 +309,40 @@ sub is_false_positive
>  	return 0;
>  }
>  
> +sub is_false_positive_32bit
> +{
> +       my ($match) = @_;
> +       state $page_offset = get_page_offset();
> +
> +       if ($match =~ '\b(0x)?(f|F){8}\b') {
> +               return 1;
> +       }
> +
> +       if (hex($match) < $page_offset) {
> +               return 1;
> +       }
> +
> +       return 0;
> +}
> +
> +# returns integer value
> +sub get_page_offset
> +{
> +       my $page_offset;
> +       my $default_offset = 0xc0000000;
> +
> +       # Allow --page-offset-32bit to override.
> +       if ($page_offset_32bit != 0) {
> +               return $page_offset_32bit;
> +       }
> +
> +       $page_offset = get_kernel_config_option('CONFIG_PAGE_OFFSET');
> +       if (!$page_offset) {
> +	       return $default_offset;
> +       }
> +       return $page_offset;
> +}
> +
>  sub is_in_vsyscall_memory_region
>  {
>  	my ($match) = @_;
> @@ -314,11 +384,13 @@ sub may_leak_address
>  
>  sub get_address_re
>  {
> -	if (is_x86_64()) {
> -		return get_x86_64_re();
> -	} elsif (is_ppc64()) {
> +	if (is_ppc64()) {
>  		return '\b(0x)?[89abcdef]00[[:xdigit:]]{13}\b';
> +	} elsif (is_32bit()) {
> +		return '\b(0x)?[[:xdigit:]]{8}\b';
>  	}
> +
> +	return get_x86_64_re();
>  }
>  
>  sub get_x86_64_re