scripts/sign-file

#!/usr/bin/perl -w
#
# Sign a module file using the given key.
#
# Format:
#
#	./scripts/sign-file [-v] <key> <x509> <module> [<dest>]
#
#
use strict;
use FileHandle;
use IPC::Open2;

my $verbose = 0;
if ($#ARGV >= 0 && $ARGV[0] eq "-v") {
    $verbose = 1;
    shift;
}

die "Format: ./scripts/sign-file [-v] <key> <x509> <module> [<dest>]\n"
    if ($#ARGV != 2 && $#ARGV != 3);

my $private_key = $ARGV[0];
my $x509 = $ARGV[1];
my $module = $ARGV[2];
my $dest = ($#ARGV == 3) ? $ARGV[3] : $ARGV[2] . "~";

die "Can't read private key\n" unless (-r $private_key);
die "Can't read X.509 certificate\n" unless (-r $x509);
die "Can't read module\n" unless (-r $module);

#
# Read the kernel configuration
#
my %config = (
    CONFIG_MODULE_SIG_SHA512 => 1
    );

if (-r ".config") {
    open(FD, "<.config") || die ".config";
    while (<FD>) {
	if ($_ =~ /^(CONFIG_.*)=[ym]/) {
	    $config{$1} = 1;
	}
    }
    close(FD);
}

#
# Function to read the contents of a file into a variable.
#
sub read_file($)
{
    my ($file) = @_;
    my $contents;
    my $len;

    open(FD, "<$file") || die $file;
    binmode FD;
    my @st = stat(FD);
    die $file if (!@st);
    $len = read(FD, $contents, $st[7]) || die $file;
    close(FD) || die $file;
    die "$file: Wanted length ", $st[7], ", got ", $len, "\n"
	if ($len != $st[7]);
    return $contents;
}

###############################################################################
#
# First of all, we have to parse the X.509 certificate to find certain details
# about it.
#
# We read the DER-encoded X509 certificate and parse it to extract the Subject
# name and Subject Key Identifier.  Theis provides the data we need to build
# the certificate identifier.
#
# The signer's name part of the identifier is fabricated from the commonName,
# the organizationName or the emailAddress components of the X.509 subject
# name.
#
# The subject key ID is used to select which of that signer's certificates
# we're intending to use to sign the module.
#
###############################################################################
my $x509_certificate = read_file($x509);

my $UNIV = 0 << 6;
my $APPL = 1 << 6;
my $CONT = 2 << 6;
my $PRIV = 3 << 6;

my $CONS = 0x20;

my $BOOLEAN	= 0x01;
my $INTEGER	= 0x02;
my $BIT_STRING	= 0x03;
my $OCTET_STRING = 0x04;
my $NULL	= 0x05;
my $OBJ_ID	= 0x06;
my $UTF8String	= 0x0c;
my $SEQUENCE	= 0x10;
my $SET		= 0x11;
my $UTCTime	= 0x17;
my $GeneralizedTime = 0x18;

my %OIDs = (
    pack("CCC", 85, 4, 3)	=> "commonName",
    pack("CCC", 85, 4, 6)	=> "countryName",
    pack("CCC", 85, 4, 10)	=> "organizationName",
    pack("CCC", 85, 4, 11)	=> "organizationUnitName",
    pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 1, 1) => "rsaEncryption",
    pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 1, 5) => "sha1WithRSAEncryption",
    pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 9, 1) => "emailAddress",
    pack("CCC", 85, 29, 35)	=> "authorityKeyIdentifier",
    pack("CCC", 85, 29, 14)	=> "subjectKeyIdentifier",
    pack("CCC", 85, 29, 19)	=> "basicConstraints"
);

###############################################################################
#
# Extract an ASN.1 element from a string and return information about it.
#
###############################################################################
sub asn1_extract($$@)
{
    my ($cursor, $expected_tag, $optional) = @_;

    return [ -1 ]
	if ($cursor->[1] == 0 && $optional);

    die $x509, ": ", $cursor->[0], ": ASN.1 data underrun (elem ", $cursor->[1], ")\n"
	if ($cursor->[1] < 2);

    my ($tag, $len) = unpack("CC", substr(${$cursor->[2]}, $cursor->[0], 2));

    if ($expected_tag != -1 && $tag != $expected_tag) {
	return [ -1 ]
	    if ($optional);
	die $x509, ": ", $cursor->[0], ": ASN.1 unexpected tag (", $tag,
	" not ", $expected_tag, ")\n";
    }

    $cursor->[0] += 2;
    $cursor->[1] -= 2;

    die $x509, ": ", $cursor->[0], ": ASN.1 long tag\n"
	if (($tag & 0x1f) == 0x1f);
    die $x509, ": ", $cursor->[0], ": ASN.1 indefinite length\n"
	if ($len == 0x80);

    if ($len > 0x80) {
	my $l = $len - 0x80;
	die $x509, ": ", $cursor->[0], ": ASN.1 data underrun (len len $l)\n"
	    if ($cursor->[1] < $l);

	if ($l == 0x1) {
	    $len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1));
	} elsif ($l = 0x2) {
	    $len = unpack("n", substr(${$cursor->[2]}, $cursor->[0], 2));
	} elsif ($l = 0x3) {
	    $len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1)) << 16;
	    $len = unpack("n", substr(${$cursor->[2]}, $cursor->[0] + 1, 2));
	} elsif ($l = 0x4) {
	    $len = unpack("N", substr(${$cursor->[2]}, $cursor->[0], 4));
	} else {
	    die $x509, ": ", $cursor->[0], ": ASN.1 element too long (", $l, ")\n";
	}

	$cursor->[0] += $l;
	$cursor->[1] -= $l;
    }

    die $x509, ": ", $cursor->[0], ": ASN.1 data underrun (", $len, ")\n"
	if ($cursor->[1] < $len);

    my $ret = [ $tag, [ $cursor->[0], $len, $cursor->[2] ] ];
    $cursor->[0] += $len;
    $cursor->[1] -= $len;

    return $ret;
}

###############################################################################
#
# Retrieve the data referred to by a cursor
#
###############################################################################
sub asn1_retrieve($)
{
    my ($cursor) = @_;
    my ($offset, $len, $data) = @$cursor;
    return substr($$data, $offset, $len);
}

###############################################################################
#
# Roughly parse the X.509 certificate
#
###############################################################################
my $cursor = [ 0, length($x509_certificate), \$x509_certificate ];

my $cert = asn1_extract($cursor, $UNIV | $CONS | $SEQUENCE);
my $tbs = asn1_extract($cert->[1], $UNIV | $CONS | $SEQUENCE);
my $version = asn1_extract($tbs->[1], $CONT | $CONS | 0, 1);
my $serial_number = asn1_extract($tbs->[1], $UNIV | $INTEGER);
my $sig_type = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $issuer = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $validity = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $subject = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $key = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $issuer_uid = asn1_extract($tbs->[1], $CONT | $CONS | 1, 1);
my $subject_uid = asn1_extract($tbs->[1], $CONT | $CONS | 2, 1);
my $extension_list = asn1_extract($tbs->[1], $CONT | $CONS | 3, 1);

my $subject_key_id = ();
my $authority_key_id = ();

#
# Parse the extension list
#
if ($extension_list->[0] != -1) {
    my $extensions = asn1_extract($extension_list->[1], $UNIV | $CONS | $SEQUENCE);

    while ($extensions->[1]->[1] > 0) {
	my $ext = asn1_extract($extensions->[1], $UNIV | $CONS | $SEQUENCE);
	my $x_oid = asn1_extract($ext->[1], $UNIV | $OBJ_ID);
	my $x_crit = asn1_extract($ext->[1], $UNIV | $BOOLEAN, 1);
	my $x_val = asn1_extract($ext->[1], $UNIV | $OCTET_STRING);

	my $raw_oid = asn1_retrieve($x_oid->[1]);
	next if (!exists($OIDs{$raw_oid}));
	my $x_type = $OIDs{$raw_oid};

	my $raw_value = asn1_retrieve($x_val->[1]);

	if ($x_type eq "subjectKeyIdentifier") {
	    my $vcursor = [ 0, length($raw_value), \$raw_value ];

	    $subject_key_id = asn1_extract($vcursor, $UNIV | $OCTET_STRING);
	}
    }
}

###############################################################################
#
# Determine what we're going to use as the signer's name.  In order of
# preference, take one of: commonName, organizationName or emailAddress.
#
###############################################################################
my $org = "";
my $cn = "";
my $email = "";

while ($subject->[1]->[1] > 0) {
    my $rdn = asn1_extract($subject->[1], $UNIV | $CONS | $SET);
    my $attr = asn1_extract($rdn->[1], $UNIV | $CONS | $SEQUENCE);
    my $n_oid = asn1_extract($attr->[1], $UNIV | $OBJ_ID);
    my $n_val = asn1_extract($attr->[1], -1);

    my $raw_oid = asn1_retrieve($n_oid->[1]);
    next if (!exists($OIDs{$raw_oid}));
    my $n_type = $OIDs{$raw_oid};

    my $raw_value = asn1_retrieve($n_val->[1]);

    if ($n_type eq "organizationName") {
	$org = $raw_value;
    } elsif ($n_type eq "commonName") {
	$cn = $raw_value;
    } elsif ($n_type eq "emailAddress") {
	$email = $raw_value;
    }
}

my $signers_name = $email;

if ($org && $cn) {
    # Don't use the organizationName if the commonName repeats it
    if (length($org) <= length($cn) &&
	substr($cn, 0, length($org)) eq $org) {
	$signers_name = $cn;
	goto got_id_name;
    }

    # Or a signifcant chunk of it
    if (length($org) >= 7 &&
	length($cn) >= 7 &&
	substr($cn, 0, 7) eq substr($org, 0, 7)) {
	$signers_name = $cn;
	goto got_id_name;
    }

    $signers_name = $org . ": " . $cn;
} elsif ($org) {
    $signers_name = $org;
} elsif ($cn) {
    $signers_name = $cn;
}

got_id_name:

die $x509, ": ", "X.509: Couldn't find the Subject Key Identifier extension\n"
    if (!$subject_key_id);

my $key_identifier = asn1_retrieve($subject_key_id->[1]);

###############################################################################
#
# Create and attach the module signature
#
###############################################################################

#
# Signature parameters
#
my $algo = 1;		# Public-key crypto algorithm: RSA
my $hash = 0;		# Digest algorithm
my $id_type = 1;	# Identifier type: X.509

#
# Digest the data
#
my ($dgst, $prologue) = ();
if (exists $config{"CONFIG_MODULE_SIG_SHA1"}) {
    $prologue = pack("C*",
		     0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
		     0x2B, 0x0E, 0x03, 0x02, 0x1A,
		     0x05, 0x00, 0x04, 0x14);
    $dgst = "-sha1";
    $hash = 2;
} elsif (exists $config{"CONFIG_MODULE_SIG_SHA224"}) {
    $prologue = pack("C*",
		     0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
		     0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
		     0x05, 0x00, 0x04, 0x1C);
    $dgst = "-sha224";
    $hash = 7;
} elsif (exists $config{"CONFIG_MODULE_SIG_SHA256"}) {
    $prologue = pack("C*",
		     0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
		     0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
		     0x05, 0x00, 0x04, 0x20);
    $dgst = "-sha256";
    $hash = 4;
} elsif (exists $config{"CONFIG_MODULE_SIG_SHA384"}) {
    $prologue = pack("C*",
		     0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
		     0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
		     0x05, 0x00, 0x04, 0x30);
    $dgst = "-sha384";
    $hash = 5;
} elsif (exists $config{"CONFIG_MODULE_SIG_SHA512"}) {
    $prologue = pack("C*",
		     0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
		     0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
		     0x05, 0x00, 0x04, 0x40);
    $dgst = "-sha512";
    $hash = 6;
} else {
    die "Can't determine hash algorithm";
}

#
# Generate the digest and read from openssl's stdout
#
my $digest;
$digest = readpipe("openssl dgst $dgst -binary $module") || die "openssl dgst";

#
# Generate the binary signature, which will be just the integer that comprises
# the signature with no metadata attached.
#
my $pid;
$pid = open2(*read_from, *write_to,
	     "openssl rsautl -sign -inkey $private_key -keyform PEM") ||
    die "openssl rsautl";
binmode write_to;
print write_to $prologue . $digest || die "pipe to openssl rsautl";
close(write_to) || die "pipe to openssl rsautl";

binmode read_from;
my $signature;
read(read_from, $signature, 4096) || die "pipe from openssl rsautl";
close(read_from) || die "pipe from openssl rsautl";
$signature = pack("n", length($signature)) . $signature,

waitpid($pid, 0) || die;
die "openssl rsautl died: $?" if ($? >> 8);

#
# Build the signed binary
#
my $unsigned_module = read_file($module);

my $magic_number = "~Module signature appended~\n";

my $info = pack("CCCCCxxxN",
		$algo, $hash, $id_type,
		length($signers_name),
		length($key_identifier),
		length($signature));

if ($verbose) {
    print "Size of unsigned module: ", length($unsigned_module), "\n";
    print "Size of signer's name  : ", length($signers_name), "\n";
    print "Size of key identifier : ", length($key_identifier), "\n";
    print "Size of signature      : ", length($signature), "\n";
    print "Size of informaton     : ", length($info), "\n";
    print "Size of magic number   : ", length($magic_number), "\n";
    print "Signer's name          : '", $signers_name, "'\n";
    print "Digest                 : $dgst\n";
}

open(FD, ">$dest") || die $dest;
binmode FD;
print FD
    $unsigned_module,
    $signers_name,
    $key_identifier,
    $signature,
    $info,
    $magic_number
    ;
close FD || die $dest;

if ($#ARGV != 3) {
    rename($dest, $module) || die $module;
}