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100 lines
3.5 KiB
Perl
Executable File
100 lines
3.5 KiB
Perl
Executable File
#!/usr/bin/env perl
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#This is a utility to scrape out the EFI boot image from an el torito enabled disk
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use strict;
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use Fcntl qw/SEEK_SET/;
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my $iso;
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my $outfile;
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GetOptions("out=s" => \$outfile,
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"iso=s" => \$iso);
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my $emul;
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my $blksize = 2048;
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my $istream;
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use Getopt::Long;
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sub grabimage {
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my $bootcat = shift;
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my $image;
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my @recdata = unpack("C2vC2vV", $bootcat);
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unless ($recdata[0] == 0x88) { printf "Error: EFI torito record not bootable\n"; exit; }
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$emul = $recdata[1];
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#for now, ignore load segment, system type
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seek($istream, $recdata[6] * $blksize, SEEK_SET);
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my $size = $recdata[5];
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if ($size == 0) { $size = 1; } #if 0/1, it's auto-detect time
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my $readbytes = read($istream, $image, $size * 512);
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if ($size == 1) { #we have to interpret the FAT header to get the real size
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seek($istream, $recdata[6] * $blksize, SEEK_SET); # go back to beginning
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my @fatheader = unpack("C11vCvC3vC11V", $image);
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my $secsize = $fatheader[11];
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if ($fatheader[17]) {
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$size = $secsize * ($fatheader[17]);
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} else {
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die "Unsupported FAT header, requires test of commented code segment";
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}
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# } elsif ($fatheader[-1]) {
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# $size=$secsize*$fatheader[-1];
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# }
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$readbytes = read($istream, $image, $size);
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}
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my $outh;
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open($outh, ">", $outfile);
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print $outh $image;
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close($outh);
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}
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if (!-r $iso) {
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printf "Error, $iso does not seem to exist or is not readable";
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exit 1;
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}
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open($istream, "<", $iso) || die "Error opening $iso";
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my $bootsect;
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seek($istream, 17 * $blksize, SEEK_SET);
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my $readbytes = read($istream, $bootsect, 0x4b);
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unless ($readbytes == 0x4b) {
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printf "Error reading boot record volume from $iso\n";
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exit 1;
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}
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my @recdata;
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@recdata = unpack("CA5CA32C32V", $bootsect); #it would have been nice if the el torito actually said little endian on it..
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unless ($recdata[0] == 0 and $recdata[1] eq 'CD001'
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and $recdata[2] == 1 and $recdata[3] eq "EL TORITO SPECIFICATION") {
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printf "Error: Boot record volume format invalid\n";
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exit 1;
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}
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my $bootcatidx = $recdata[-1];
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my $bootcat;
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seek($istream, $bootcatidx * $blksize, SEEK_SET);
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$readbytes = read($istream, $bootcat, 0x20);
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unless ($readbytes == 0x20) { printf "Error reading boot catalog at $bootcatidx\n"; exit 1; }
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@recdata = unpack("C*", $bootcat);
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unless ($recdata[0] == 1 and $recdata[0x1e] == 0x55 and $recdata[0x1f] == 0xaa) {
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printf "Boot catalog has invalid header\n"; exit 1;
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}
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$readbytes = read($istream, $bootcat, 0x20);
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my $image;
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unless ($readbytes == 0x20) { printf "Error reading default El torito record\n"; exit; }
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if ($recdata[1] == 0xef) { #wow, the efi record came first, actually interpret that first record
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grabimage($bootcat);
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} else { # keep looking for an *EFI* record
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#read in first header
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read($istream, $bootcat, 0x20);
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@recdata = unpack("CCv", $bootcat);
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while ($recdata[0] == 0x90 and $recdata[1] != 0xef) {
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my $additionalrecords = $recdata[2];
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while ($additionalrecords) {
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read($istream, $bootcat, 0x20); #throw away irrelevant sectors
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$additionalrecords -= 1;
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}
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read($istream, $bootcat, 0x20); #throw away irrelevant sectors
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@recdata = unpack("CCv", $bootcat);
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}
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if ($recdata[1] != 0xef) {
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printf "No EFI boot image found\n";
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exit 1;
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}
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$readbytes = read($istream, $bootcat, 0x20);
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grabimage($bootcat);
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}
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