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Date: Sat, 6 Jan 2018 09:12:28 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: kaiwan.billimoria@...il.com
Cc: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v5] leaking_addresses: add generic 32-bit support

Hi Kaiwan,

Thanks for the patch

On Thu, Jan 04, 2018 at 05:51:25PM +0530, kaiwan.billimoria@...il.com wrote:
> The script now attempts to detect the architecture it's running upon; as of now,
> we explicitly support x86_64, PPC64, ARM64, MIPS64 and x86_32.

This is incorrect. We do not currently support ARM64, MIPS64 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: "--opt-32bit" 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).
> 
> Currently, code (or "rules") to detect special cases for x86_64, PPC64 and Aarch64
> (in the get_address_re sub) is present. 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 into the code, in future, as applicable.
> 
> This patch adds support for ix86 and generic 32 bit architectures.
>  - Add command line option for generic 32-bit checking.
>  - 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.

This is all pretty confusing. It is hard to discern what is the
description of the problem being fixed and what is the description of
the new behaviour implemented by the patch. Also this patch does not add
kernel configuration file option. 

> The script has been lightly tested on the following systems:
>  x86_64
>  x86_32 (on a i686 running Debian 7 to be precise)
>  ARM32  (on a Yocto-based qemuarm32 ARM Versatile platform (ARM926EJ-S cpu))
> 
> In the first two cases, one just has to run the script - no parameters required.
> In the ARM-32 case, it will, by design, fail to detect the architecture;
> (re)running it with the '--32-bit' and/or the '--page-offset-32bit=<hexval>'

This does not match the code. In the code you have defined the option as
'--opt-32bit'? '--32-bit' is better ;)

> option switch(es) has the desired effect: it now detects 32-bit leaking kernel
> addresses, if any.
> 
> Request more testing on the above and other platforms.
> 
> 
> Signed-off-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
> 
> ---
>  scripts/leaking_addresses.pl | 190 +++++++++++++++++++++++++++++++++++--------
>  1 file changed, 156 insertions(+), 34 deletions(-)
> 
> diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
> index a29e13e577a7..b0807b3a3c7c 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>
> -

Please make only the minimum number of changes required.

> +# (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).
>  #
> @@ -32,11 +32,6 @@ my @DIRS = ('/proc', '/sys');
>  # Timer for parsing each file, in seconds.
>  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');
> -
>  # Command line options.
>  my $help = 0;
>  my $debug = 0;
> @@ -48,7 +43,9 @@ 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.

No need for this to be removed and re-added (if you line up the comments).

> +my $opt_32_bit = 0;            # Detect (only) 32-bit kernel leaking addresses.

As previously discussed, please be consistent in naming: $opt_32bit

> +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',
> @@ -104,10 +101,12 @@ 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)
> +	--opt-32bit			Detect (only) 32-bit kernel leaking addresses.

  	--32-bit			Scan 32-bit kernel.

> +	--page-offset-32bit=<hex>	PAGE_OFFSET value (for 32-bit kernels).
>  	-d, --debug			Display debugging output.
> -	-h, --help, --versionq		Display this help and exit.
> +	-h, --help, --version		Display this help and exit.
>  
> -Scans the running (64 bit) kernel for potential leaking addresses.
> +Scans the running kernel for potential leaking addresses.
>  
>  EOM
>  	exit($exitcode);
> @@ -123,7 +122,9 @@ GetOptions(
>  	'squash-by-path'        => \$squash_by_path,
>  	'squash-by-filename'    => \$squash_by_filename,
>  	'raw'                   => \$raw,
> -	'kernel-config-file=s'	=> \$kernel_config_file,
> +	'opt-32bit'             => \$opt_32_bit,
> +	'page-offset-32bit=o'   => \$page_offset_32bit,
> +	'kernel-config-file=s'  => \$kernel_config_file,
>  ) or help(1);
>  
>  help(0) if ($help);
> @@ -139,16 +140,15 @@ 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;
>  
> -	my $archname = $Config{archname};
> -	printf "\n\$ perl -MConfig -e \'print \"\$Config{archname}\\n\"\'\n";
> -	printf "%s\n", $archname;
> +if (!is_known_architecture()) {
> +	printf STDERR "\nFATAL: Script does not recognize your architecture\n";
> +
> +	my $arch = `uname -m`;
> +	chomp $arch;
> +	printf "\n\$ uname -m\n";
> +	printf "%s\n", $arch;
>  
>  	exit(129);
>  }

I am going to add a patch to use `uname -m` instead of `perl -MConfig
...` on powerpc. Please rebase your next version. 

> @@ -168,21 +168,45 @@ sub dprint
>  	printf(STDERR @_) if $debug;
>  }
>  
> -sub is_supported_architecture
> +sub is_known_architecture

Please don't change this.

>  {
> -	return (is_x86_64() or is_ppc64());
> +	return (is_64bit() or is_32bit());
>  }
>  
> -sub is_x86_64
> +sub is_32bit
>  {
> -	my $archname = $Config{archname};
> +	# 32-bit actual case
> +	if (is_ix86_32()) {
> +		return 1;
> +	}
>  
> -	if ($archname =~ m/x86_64/) {
> +	# 32-bit "forced" case (for any arch other than IA-32)
> +	if ($opt_32_bit or $page_offset_32bit) {
>  		return 1;
>  	}
>  	return 0;
>  }

Perhaps


sub is_32bit
{
	# Allow --32-bit and/or --page-offset-32bit to override.
	if ($opt_32_bit or $page_offset_32bit) {
		return 1;
	}

	if (is_ix86_32()) {
		return 1;
	}

	return 0;
}


> +sub is_64bit
> +{
> +	return (is_x86_64() or is_ppc64() or is_arm64() or is_mips64());
> +}
> +
> +sub is_x86_64
> +{
> +	is_arch("x86_64");
> +}
> +
> +sub is_arm64
> +{
> +	is_arch("aarch64");
> +}
> +
> +sub is_mips64
> +{
> +	is_arch("mips64");
> +}
> +

We cannot add these last two. There has been no talk (to my knowledge) of the
address format for mips64 or aarch64. If you have tested for these please
add as a separate patch.

>  sub is_ppc64
>  {
>  	my $archname = $Config{archname};
> @@ -193,6 +217,47 @@ sub is_ppc64
>  	return 0;
>  }
>  
> +sub is_ix86_32
> +{
> +	my $arch = `uname -m`;
> +
> +	chomp $arch;
> +	if ($arch =~ m/i[3456]86/) {
> +		return 1;
> +	}
> +	return 0;
> +}
> +
> +sub is_arch
> +{
> +	my ($desc) = @_;
> +	my $arch = `uname -m`;
> +
> +	chomp $arch;
> +	if ($arch eq $desc) {
> +		return 1;
> +	}
> +	return 0;
> +}
> +
> +sub show_detected_architecture
> +{
> +	printf "Detected architecture: ";
> +	if (is_32bit()) {
> +		printf "32 bit\n";

is_32bit includes the command line options so this is not _totally_
correct. Prefer

	 if (is_x64_32()) {
		...

> +	} elsif (is_x86_64()) {
> +		printf "x86_64\n";
> +	} elsif (is_ppc64()) {
> +		printf "PPC64\n";
> +	} 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
>  {
> @@ -212,7 +277,6 @@ sub get_kernel_config_option
>  		} else {
>  			@config_files = ($tmp_file);
>  		}
> -

Please don't do white space changes in the middle or another patch.

>  	} else {
>  		my $file = '/boot/config-' . `uname -r`;
>  		chomp $file;
> @@ -220,7 +284,6 @@ sub get_kernel_config_option
>  	}
>  
>  	foreach my $file (@config_files) {
> -		dprint("parsing config file: %s\n", $file);

This should be a separate patch. 'One thing per patch' is the kernel mantra

>  		$value = option_from_file($option, $file);
>  		if ($value ne "") {
>  			last;
> @@ -258,6 +321,14 @@ sub is_false_positive
>  {
>  	my ($match) = @_;
>  
> +	# 32 bit architectures, actual or forced
> +

No need for this comment.

> +	if (is_32bit()) {
> +		return is_false_positive_32bit($match);
> +	}
> +
> +	# 64 bit architectures
> +

Or this one.

>  	if ($match =~ '\b(0x)?(f|F){16}\b' or
>  	    $match =~ '\b(0x)?0{16}\b') {
>  		return 1;
> @@ -281,6 +352,58 @@ sub is_in_vsyscall_memory_region
>  	return ($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 $addr32 = hex($match);
> +	if ($addr32 < $page_offset) {
> +		return 1;
> +	}
> +
> +	return 0;
> +}

The return value of this sub routine is confusing. Either it should be
commented as returning a hex value or it should return a string. I
prefer a string since the rest of the subs in the file return strings,
less cognitive load to keep everything the same. Unless there is some
clear advantage to returning a hex value (which I cannot see).

> +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;
> +	}
> +
> +	$page_offset = get_kernel_config_option('CONFIG_PAGE_OFFSET');
> +	return $default_offset;
> +}

This is wrong.

> +
> +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;
> +}
> +

When do you call this subroutine?

>  # True if argument potentially contains a kernel address.
>  sub may_leak_address
>  {
> @@ -300,8 +423,6 @@ sub may_leak_address
>  	}
>  
>  	$address_re = get_address_re();
> -	dprint("Kernel address regular expression: %s\n", $address_re);
> -

Please see comments above on 'one thing per patch'.

>  	while (/($address_re)/g) {
>  		if (!is_false_positive($1)) {
>  			return 1;
> @@ -313,16 +434,17 @@ sub may_leak_address
>  
>  sub get_address_re
>  {
> -	my $re;
> +	my $re = "";
>  
>  	if (is_x86_64()) {
>  		$re = get_x86_64_re();
>  	} elsif (is_ppc64()) {
>  		$re = '\b(0x)?[89abcdef]00[[:xdigit:]]{13}\b';
> -	}
> -
> -	if ($re eq "") {
> -		print STDERR "$0: failed to build kernel address regular expression\n";
> +	###
> +	# 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;

This is messy. We definitely want to warn if we cannot fully determine
the correct regex to use. Also, if you would like to default to 32-bit
you will need to back it up with some reasoning. Currently there is no
default if the correct regex cannot be ascertained. At this stage I feel
this is the correct behaviour, I'm open to discussion though.

> -- 
> 2.14.3


thanks,
Tobin.

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