Exploring the Pippin ROM(s), part 6: Back in the ‘rvpr’

(How’s that for a punny subtitle?)

It’s been a while. I haven’t lost interest, I’ve just been busy with work and other things. Life has a funny way of sneaking up on you. 😉

The wait is worth it, though. Buckle up; this one’s a doozy.

Apple hasn’t documented the Pippin’s authentication process beyond what developers needed to know. There exists a technote that was distributed via the SDK(s) that gives an overview of what developers were expected to do to get their discs signed before final mastering and duplication. The Pippin’s authenticated boot process hinges upon the presence of a specially-crafted, RSA-signed file unique to each disc called the “PippinAuthenticationFile.” Since the Pippin platform was abandoned and subsequently cancelled in 1998, Apple no longer signs Pippin discs nor have they made available the means for third parties to do so. To my knowledge, most of the specifics of how the PippinAuthenticationFile plays a role in the Pippin’s boot process have never been documented outside of Apple.

That changes today.

This post is pretty dense, so I highly recommend (re-)reading parts 1 through 4 for some background before getting too deep. Otherwise, here’s a quick recap: during every boot, a retail Pippin console locates a potential boot volume on CD, loads an ‘rvpr’ 0 resource from ROM, then calls the code therein in order to verify that the target volume passes an authentication check allowing it to boot the system. (An aside: Previously, I asserted that while I found identical copies of ‘rvpr’ 0 in the 1.2 and 1.3 ROMs, I couldn’t find an entry for it in the resource map, therefore it must either be dead code or called some other way. This conclusion turned out to be incorrect—the resource map is not contiguous in ROMs 1.2 and 1.3, which made manually searching it more difficult, but it does indeed contain an entry for ‘rvpr’ 0. The authentication process is therefore identical between ROM 1.0 and 1.2.) When I last looked at ‘rvpr’ 0, I was stymied by a routine called upon entry which, absent of any symbols to help point me toward its purpose, I conjectured used a complex block of data at the end of the resource to “decrypt” the code therein. After taking a closer look a few days ago, I was delighted to find that its purpose is much simpler—it exists to patch the absolute memory locations in the code so they are relative to the buffer where ‘rvpr’ 0 is loaded. Without these patches, the code would crash the Pippin on boot practically every time!

The way this routine accomplishes this is kind of elegant. We initialize a cursor pointer to the beginning of our buffer where ‘rvpr’ 0 is loaded. The offset table starting at offset $8A47 from the start of ‘rvpr’ 0 begins with a 32-bit longword defining the size of the table. Then, the table itself is compressed: a byte with bit 7 set means it’s a relative sign-extended 7-bit offset from our cursor position, a byte with bit 6 set means it along with the next byte form a sign-extended 14-bit offset from our cursor position, but if both bit 6 and 7 are clear, then combine the next three bytes to form a 30-bit absolute cursor position. Multiply these offsets by two before applying them (because 68K opcodes are always at least two bytes), add the address of our ‘rvpr’ 0 buffer to the 32-bit longword pointed to by our cursor, then repeat the process until we’ve exhausted the offset table. Easy peasy.

5E   1218         Move.B   (A0)+, D1   ; grab the next byte into D1, we'll call it the command byte
60   1001         Move.B   D1, D0
62   0240 0080    AndI     #$80, D0    ; is bit 7 set?
66   670C         BEQ.B    @checkBit6  ; then handle the bit 6 case

; command byte bit 7 is set, so
; D2 += signExtend(D1 * 2) as a byte (* 2 because alignment)
68   D201         Add.B    D1, D1
6A   1001         Move.B   D1, D0
6C   4880         Ext      D0
6E   48C0         Ext.L    D0
70   D480         Add.L    D0, D2
72   6028         Bra.B    @gotOffset

; else, command byte bit 7 not set...
74   1E81         Move.B   D1, (A7)         ; put D1 into the highest byte of temp
76   1F58 0001    Move.B   (A0)+, $1(A7)    ; grab the next byte into the 2nd byte of temp
7A   1001         Move.B   D1, D0
7C   0240 0040    AndI     #$40, D0         ; is bit 6 of D1 set?
80   670C         BEQ.B    @get32BitOffset  ; yes? then

; command byte bit 6 is set, so
; our address offset is only 14 bits
82   3017         Move     (A7), D0    ; grab the new temp into D0
84   E548         LsL      #2, D0      ; D0 <<= 2
86   E240         AsR      #1, D0      ; D0 /= 2
88   48C0         Ext.L    D0          ; sign extend it
8A   D480         Add.L    D0, D2      ; D0 is the found offset * 2 (because alignment), add to our current offset
8C   600E         Bra.B    @gotOffset  ; apply it

; bit 6 not set...
8E   1F58 0002    Move.B   (A0)+, $2(A7)  ; grab the next byte into the 3rd byte of temp
92   1F58 0003    Move.B   (A0)+, $3(A7)  ; grab the next byte into the 4th byte of temp
96   2417         Move.L   (A7), D2       ; D2 is a brand new offset!
98   E58A         LsL.L    #2, D2         ; D2 <<= 2
9A   E282         AsR.L    #1, D2         ; D2 /= 2

; D2 == the offset we want to apply to argument 2
; D6 == the offset we want to apply to the longword found there (typically @start)
9C   DDB1 2800    Add.L    D6, $0(A1,D2.L)  ; add D6 to the longword at (@start + D2)
A0   5385         SubQ.L   #1, D5
A2   4A85         Tst.L    D5               ; are we out of longs to patch?
A4   6EB8         BGT.B    @loopBody

Now that we've "unpacked" the code of 'rvpr' 0, let's dig into it. 🙂

main starts off initializing a number of globals, first by calling InitRSAAlgorithmChooser and then a handful of other subroutines. It then initializes some local variables on the stack: previous A4, values related to the PippinAuthenticationFile, and a ParamBlockRec for calls to _Read. In addition, among those locals is a 16-byte temporary buffer for digests created during the main loop.

Recall from part 2 that the Pippin ROM passes as input to 'rvpr' 0 the following arguments: two pointers to some as-of-yet-unknown data in ROM shortly preceding the callsite, the ID of the boot volume candidate, and the refNum of the candidate's disk driver. After we've initialized our variables, we hit the ground running by calling GetVolAuthFileInfo to fetch the offset to and size of the PippinAuthenticationFile. Note that if at any point during 'rvpr' 0 one of its internal subroutines fails, the entire process is reported as having failed the authentication check.

24C   41EE FFAA         Lea.L     -$56(A6), A0    ; A0 -> temp var for created digests
250   2E08              Move.L    A0, D7          ; D7 == ptr to temp digest
252   486E FFCA         Pea.L     -$36(A6)        ; pass size out address
256   486E FFBE         Pea.L     -$42(A6)        ; pass offset out address
25A   3F05              Move      D5, -(A7)       ; $10(A6) is dqDrive passed in from ROM
25C   3F2E 0012         Move      $12(A6), -(A7)  ; $12(A6) is dqRefNum passed in from ROM
260   4EB9 0000 03E6    Jsr       GetVolAuthFileInfo
266   3600              Move      D0, D3
268   4A43              Tst       D3
26A   4FEF 000C         Lea.L     $C(A7), A7
26E   6600 0142         BNE       @mainCleanup    ; if GetVolAuthFileInfo returns nonzero, fail
272   202E FFBE         Move.L    -$42(A6), D0    ; D0 = offset from start of HFS volume to PippinAuthenticationFile in allocation blocks
276   7209              MoveQ.L   #9, D1
278   E3A8              LsL.L     D1, D0          ; D0 = offset from start of HFS volume to PippinAuthenticationFile in bytes
27A   2D40 FFC6         Move.L    D0, -$3A(A6)    ; save the offset into -$3A(A6)
27E   202E FFCA         Move.L    -$36(A6), D0    ; D0 = size of the PippinAuthenticationFile in bytes
282   A11E              _NewPtr
284   2648              MoveA.L   A0, A3
286   200B              Move.L    A3, D0
288   4A80              Tst.L     D0
28A   660E              BNE.B     @gotAuthBuffer  ; if _NewPtr returns null, clean up the stack, and fail
28C   554F              SubQ      #2, A7
28E   3EB8 0220         Move      (MemErr), (A7)
292   301F              Move      (A7)+, D0
294   3600              Move      D0, D3
296   6000 011A         Bra       @mainCleanup

29A   3D6E 0012 FFE6    Move      $12(A6), ioRefNum(A6)
2A0   3D45 FFE4         Move      D5, ioVRefNum(A6)         ; dqDrive
2A4   2D4B FFEE         Move.L    A3, ioBuffer(A6)
2A8   2D6E FFCA FFF2    Move.L    -$36(A6), ioReqCount(A6)  ; size of the PippinAuthenticationFile
2AE   3D7C 0001 FFFA    Move      #fsFromStar, ioPosMode(A6)
2B4   202E FFBE         Move.L    -$42(A6), D0              ; offset from start of HFS volume to PippinAuthenticationFile in device blocks
2B8   7209              MoveQ.L   #9, D1
2BA   E3A8              LsL.L     D1, D0                    ; get the offset in bytes by multiplying by device block size (512 bytes)
2BC   2D40 FFFC         Move.L    D0, ioPosOffset(A6)
2C0   41EE FFCE         Lea.L     -$32(A6), A0
2C4   A002              _Read
2C6   3600              Move      D0, D3
2C8   4A43              Tst       D3
2CA   6600 00E6         BNE       @mainCleanup              ; if _Read returns something other than noErr, fail

Following this call, we allocate enough space for the file by calling _NewPtr. We then call _Read with our local ParamBlockRec filled with the disk driver refNum, the volume refNum, the pointer to the buffer we just allocated, our buffer's size, and the byte offset to the authentication file on our candidate. Armed with the contents of the PippinAuthenticationFile, we then pass them to VerifyDigestInfo to verify the signature contained therein. If that succeeds, we're clear to start verifying the candidate's contents against this file, so we allocate temp space large enough to load a single "chunk" of data from the candidate to be hashed and verified.

Every Pippin except the KMP 2000 shipped with a built-in 4x speed CD-ROM drive. A 1x CD-ROM drive can read data at a rate of 150KB/sec, which is the speed necessary for smooth playback of audio CDs. A 2x drive doubles that rate to 300KB/sec, a 4x drive quadruples it to 600KB/sec, and so on. At 600KB/sec, it would take a Pippin almost a full minute to read just over 35MB, and nearly 20 minutes to read the entire contents of a 700MB CD-ROM. Even the KMP 2000 with its 8x drive would take almost 10 minutes to do the same. Hashing the entire contents of a CD during every boot would be unacceptable at this speed, and since the Pippin only takes a couple seconds to verify a disc at startup, it's clearly not verifying the whole thing. So what does the Pippin do?

320   4A86               Tst.L     D6
322   6604               BNE.B     @pickRandomChunk
324   7800               MoveQ.L   #0, D4
326   6016               Bra.B     @readChunk

328    202B 004C         Move.L    $4C(A3), D0  ; longword after the 128K size field at $48, appears to be number of entries in table
32C    5380              SubQ.L    #1, D0
32E    2F00              Move.L    D0, -(A7)    ; upper bound == total number of chunks
330    4878 0001         Pea.L     ($1)         ; lower bound == 1
334    4EB9 0000 0814    Jsr       RangedRand   ; patched
33A    2800              Move.L    D0, D4       ; D4 == pseudorandom integer between [1, <total number of chunks>]?
33C    504F              AddQ      #8, A7       ; clean up stack

33E    2004              Move.L    D4, D0               ; D0 == pseudorandom integer in the lowword, probably
340    2205              Move.L    D5, D1               ; D1 == 128K? 0 x 0002 0000
342    4EB9 0000 0116    Jsr       _D0timesD1           ; patched, does some weird multiplication, returns in D0
348    2D40 FFFC         Move.L    D0, ioPosOffset(A6)  ; D0 == the pseudorandom integer * 128K? D0 == offset to random 128K chunk in disc?
34C    41EE FFCE         Lea.L     -$32(A6), A0
350    A002              _Read
352    3600              Move      D0, D3
354    4A43              Tst       D3
356    665A              BNE.B     @mainCleanup

Put simply, the Pippin randomly spot-checks the candidate volume's contents every boot. The PippinAuthenticationFile isn't just a key, it isn't just a single hash—it is in fact a collection of hashes corresponding to as many 128K chunks of data that make up the boot volume. main enters a loop that iterates six times: the first check, it loads the first 128K of the volume containing important metadata about the HFS filesystem into our temporary buffer, and then verifies that data against its corresponding digested hash previously loaded from the PippinAuthenticationFile. The remaining five checks, it does the same, but on randomly selected other 128K chunks of the volume. This way, the Pippin only has to load and verify 768K—a process that takes less than a couple seconds on its 4x CD-ROM drive. But because this loop selects five of those six input chunks at random each run-through, the PippinAuthenticationFile still needs digests of the entire volume. For it's not known ahead of time which five chunks will be verified and furthermore, they rarely will be the same five chunks.

Examining several PippinAuthenticationFile examples with this code in mind quickly reveals how this file is structured. Both the chunk size and the total number of chunks in the volume are stored in a common header. This loop uses that information to determine the upper bound of which chunks to select at random and how large. Following these two fields is a table of digested 128-bit hashes corresponding, in sequential order, to the chunks in the volume. Finally, there is a signature near the end of the file, which gets verified in the call to VerifyDigestInfo before entering the loop. The process by which a PippinAuthenticationFile is created, therefore, is essentially as follows:

  1. Get the size of the target volume.
  2. Integer divide this size into 128K chunks. Call the total number of chunks N.
  3. Allocate 80 bytes for a file header.
  4. Multiply N chunks by the 16-byte size of each digest (N * 16). Call this table size T. Allocate T bytes for digests of each 128K chunk.
  5. Allocate 16 bytes for the signature size S.
  6. Pad the signature size until it is a multiple of 16 bytes (((S + 16) % 16) *16). Call this padded size P. Allocate P bytes for the signature itself.
  7. Pad additional bytes until the total file size is the next multiple of the device block size (512 bytes). The total file size therefore should be ((80 + T + 16 + P + 512) % 512) * 512.
  8. Preallocate a blank version of this file on the target volume.
  9. Starting at offset 80, compute and store a 16-byte (128-bit) digest for each of the N sequential 128K chunks. Note that to compute the digests for the entire finalized volume correctly, this file must already exist in the filesystem. It is therefore necessary to compute the size of this file in advance, preallocate a "dummy" version of it on the target volume, then compute the digests and overwrite the file in-place.
  10. At offset 80 + T + 15, store the signature size S as a byte (only one byte at the end of this space is actually used, the rest are zeroes).
  11. At offset 80 + T + 16 + 3, store the signature itself. The signature always seems to be 45 bytes long, placed such that it ends on a 16-byte boundary, explaining the extra 3-byte offset.
  12. Fill in the file header at the beginning of the file:
    • offset 0 (4 bytes): offset to signature size byte (80 + T + 15)
    • offset 4 (4 bytes): longword equal to zero (version?)
    • offset 8 (64 bytes): copyright notice (60 bytes, zero-padded right)
    • offset 72 (4 bytes): chunk size longword equal to 128K, or $20000
    • offset 76 (4 bytes): chunk count longword equal to N

Apple probably provided a tool that automated this process for stamping houses. Said tool presumably would have named the aforementioned file "PippinAuthenticationFile" with type/creator 'PpnV'/'PpnA' and saved it to the filesystem root. I imagine that this same tool likely would have filled the file's contents in-place with the signed version received from Apple. However, I have never seen such a tool in the wild so this is pure speculation on my part.

Incidentally, the name, placement within the folder hierarchy, and type/creator codes of the authentication file itself are inconsequential. The Pippin makes no HFS calls to locate the PippinAuthenticationFile—it could technically be buried within a nest of folders or named "FoobarAuthenticationFile." The verification code does not care. Instead, it fetches the Master Directory Block—512 bytes located at byte offset 1024 from the start of the boot volume. The "logical" MDB is a data structure 161 bytes in size and found immediately at the start of this "physical" MDB. However, that leaves 351 bytes unaccounted for. For Pippin CD-ROMs, Apple chose to set aside two 32-bit longwords at the end of the physical MDB for the purpose of locating the PippinAuthenticationFile at the block level. The first of these longwords defines the offset, in 512-byte blocks from the start of the volume, to the contents of the authentication file. The second of these longwords define the authentication file's size in bytes.

(As an aside, this mechanism is one reason why deleting the PippinAuthenticationFile and naively replacing it with a new version at the filesystem level is not likely to work. The new file would likely reside starting at a different allocation block in the volume; the offset in the MDB would still point to where the deleted file was/is, and HFS wouldn't know to patch it up—why should it?)

One important component of creating the authentication file, and verifying against it, is the concept of chunk "cleansing." Once the loop selects and loads a chunk, it passes it to CleanseInputChunk to optionally "cleanse" it. What does that mean in this context?

358   2F2E FFCA         Move.L    -$36(A6), -(A7)         ; size of the PippinAuthenticationFile in bytes
35C   2F2E FFC6         Move.L    -$3A(A6), -(A7)         ; offset from start of HFS volume to PippinAuthenticationFile in bytes
360   2F05              Move.L    D5, -(A7)               ; 128K
362   2F2E FFFC         Move.L    ioPosOffset(A6), -(A7)  ; the computed offset
366   2F0A              Move.L    A2, -(A7)               ; working chunk buffer
368   4EB9 0000 049A    Jsr       CleanseInputChunk       ; patched, remove the auth file from this chunk if we happened to land on it

The digested hashes contained within the authentication file do not include hashing the authentication file itself, for obvious reasons. Similarly, certain fields in the MDB should not be hashed because they change upon writing the final signed authentication file to the volume. "Cleansing" solves this problem by zeroing out these areas before hashing and digesting them. While creating an authentication file, the blocks of the volume containing the file itself should be zeroed out when hashing, and likewise most of the MDB. Upon loading a chunk, the verification loop checks its offset to see whether the chunk overlaps the MDB or the authentication file. If so, it zeroes out that data so that the digested hash matches the corresponding one stored in the authentication file.

I was going to recreate this diagram in Illustrator, but then I remembered I suck at Illustrator.

Finally, the loop passes the chunk to CreateDigest, and compares its result byte-for-byte with the digest in the authentication file by calling CompareDigests. If all six digested chunks match what's found in the authentication file, we pass the check (and can boot from this volume! Yay!). Otherwise, we return -1 to indicate failure.

36E   2F07              Move.L    D7, -(A7)       ; D7 -> out buffer for temp digest
370   2F05              Move.L    D5, -(A7)       ; chunk size (128K)
372   2F0A              Move.L    A2, -(A7)       ; cleansed working chunk buffer
374   4EB9 0000 06EE    Jsr       CreateDigest    ; patched
37A   3600              Move      D0, D3
37C   4A43              Tst       D3
37E   4FEF 0020         Lea.L     $20(A7), A7     ; clean up stack
382   662E              BNE.B     mainCleanup
384   2F07              Move.L    D7, -(A7)       ; D7 -> the digest we just created
386   2004              Move.L    D4, D0          ; D4 == which chunk this is
388   E988              LsL.L     #4, D0          ; D4 == chunk * 16 bytes (128 bit hash per chunk)
38A   206E FFC2         MoveA.L   -$3E(A6), A0    ; A0 -> chunk hashes
38E   D1C0              AddA.L    D0, A0          ; A0 -> hash of this chunk
390   4850              Pea.L     (A0)
392   4EB9 0000 07D4    Jsr       CompareDigests  ; patched, returns zero in D0 if digests match
398   7200              MoveQ.L   #0, D1
39A   1200              Move.B    D0, D1
39C   3601              Move      D1, D3
39E   4A43              Tst       D3
3A0   504F              AddQ      #8, A7          ; clean up stack
3A2   6704              BEQ.B     @nextMainForLoopIteration
3A4   76FF              MoveQ.L   #-1, D3         ; D3 == -1, fail
3A6   600A              Bra.B     mainCleanup

3A8    5286              AddQ.L    #1, D6

3AA    7006              MoveQ.L   #6, D0
3AC    BC80              Cmp.L     D0, D6
3AE    6D00 FF70         BLT       @topOfMainForLoop

So what's left?

Of the named functions I found in part 2, only four of them I have yet to step through and understand:

main done
GetVolAuthFileInfo done
CleanseInputChunk done
VerifyDigestInfo in progress
VerifySignature to do
CreateDigest in progress
CompareDigests done
RangedRand done
CleanseVCB done
GetVAFileInfoGivenMDB done
InitRSAAlgorithmChooser in progress

Astute readers may notice that I have provided sparse details about the functions related to dealing with digests and signatures so far. Those are next on my list but will also be the hardest to grok because I'll be more or less "flying solo" without any symbols whatsoever to guide me. Fortunately I have a passing familiarity with the RSA algorithm so I have a vague idea of what logic to look for. I have already found functions for 32-bit multiply and 32-bit modulo, both of which are essential for RSA.

In part 4 I explored hacking the Apple Partition Map to load custom disk drivers before the authentication check takes effect. I was not successful with that experiment and decided not to pursue it further, but my discoveries here reveal a possible alternate avenue to explore: additional partitions. The authentication check is performed on the boot volume, and only the boot volume (emphasis on each word). The partition map is not included in the check, nor are any other partitions. It should be totally possible to take an existing signed Pippin disc with unpartitioned free space available (for example, the "Tuscon" disc) and graft an additional HFS partition containing whatever apps or documents one might want. The OS should mount the other partition as it would normally, without performing any checks beyond what would be done on a real Mac.

I leave that as an exercise for the reader. I'm going after the big fish: authoring an entire homebrew disc from scratch.

Exploring the Pippin ROM(s), part 5: Open Firmware

According to the NetBSD/macppc FAQ, Open Firmware “is part of the boot ROMs in most PowerPC-based Macintosh systems, and we use it to load the kernel from disk or network.”

Turns out, “most PowerPC-based Macintosh systems” happens to include the Pippin. If you have the rare keyboard/tablet (or an ADB keyboard via the AppleJack dongle) attached and hold down Command-Option-O-F at startup, the Pippin boots to an Open Firmware prompt. However, you won’t see anything on screen because it outputs to a serial console by default; specifically, all console I/O is handled through the GeoPort. My Mac Plus happens to sit next to my Pippin, so tonight I temporarily switched my ImageWriter II’s cable over, booted both machines, and fired up ZTerm.

The following is what I discovered.

Open Firmware, PipPCI.
To continue booting the MacOS type:
To continue booting from the default boot device type:
0 > dev / ls
FF829230: /PowerPC,603@0
FF829B28: /chosen@0
FF829C58: /memory@0
FF829DA0: /openprom@0
FF829E60: /AAPL,ROM@FFC00000
FF82A088: /options@0
FF82A528: /aliases@0
FF82A6F0: /packages@0
FF82A778:   /deblocker@0,0
FF82AF78:   /disk-label@0,0
FF82B4B8:   /obp-tftp@0,0
FF82D8F8:   /mac-files@0,0
FF82E0F0:   /mac-parts@0,0
FF82E850:   /aix-boot@0,0
FF82ECC8:   /fat-files@0,0
FF830298:   /iso-9660-files@0,0
FF830BE0:   /xcoff-loader@0,0
FF8315A0:   /terminal-emulator@0,0
FF831638: /aspen@F2000000
FF832900:   /gc@10
FF832D38:     /scc@13000
FF832E90:       /ch-a@13020
FF833540:       /ch-b@13000
FF833BF0:     /awacs@14000
FF833CD8:     /swim3@15000
FF834DE0:     /via-cuda@16000
FF835970:       /adb@0,0
FF835A60:         /keyboard@0,0
FF8361B0:         /mouse@1,0
FF836260:       /pram@0,0
FF836310:       /rtc@0,0
FF8367D8:       /power-mgt@0,0
FF836898:     /mesh@18000
FF838418:       /sd@0,0
FF839048:       /st@0,0
FF839CC8:     /nvram@1D000
FF839DA0: /taos@F0800000
FF839EC8: /aspenmemory@F8000000
0 > dev /openprom  ok
0 > .properties
name                    openprom
model                   Open Firmware, PipPCI.

0 > printenv auto-boot?

auto-boot?          true                true
0 > printenv use-nvramrc?

use-nvramrc?        false               false
0 > printenv real-base

real-base           -1                  -1
0 > printenv load-base

load-base           4000                4000
0 > printenv boot-device

boot-device         /AAPL,ROM           /AAPL,ROM
0 > printenv boot-file

0 > printenv input-device

input-device        ttya                ttya
0 > printenv output-device

output-device       ttya                ttya
0 > printenv nvramrc

0 > printenv boot-command

boot-command        boot                boot
0 > bye

This dump was generated on my @WORLD Pippin with ROM 1.2. Some observations:

  • OF doesn't report a version number, instead reporting "PipPCI" in its place. Searching the ROM for strings reveals "June 28, 1996" as the latest date I could find, so whatever Apple was using in its Power Macs at that time I imagine is what is running here.
  • The ROM is located at 0xFFC00000, which follows what I've seen from hardcoded addresses I've found.
  • "taos" is the video hardware starting at 0xF0800000. I'm not sure offhand if that address is the base of video memory, but I do know from the Pegasus Prime code that taos does allow for writing directly to VRAM.
  • There is a TFTP package(!)-- wonder how it works?
  • The Pippin has a SWIM III chip onboard. There is an official floppy drive expansion dock and an unofficial floppy drive expansion board, both of which appear to be "dumb" hardware that merely connect a drive directly to pins of the Pippin's X-PCI connector on the underside of the system. The drive itself is powered and controlled entirely by hardware already built in to the Pippin. However, as far as I know, the SWIM II and later floppy controllers (including the SWIM III) lack the low-level access necessary for HD20 support, so large drives emulated by hardware such as the Floppy Emu will not work.

Exploring the Pippin ROM(s), part 4: Enter the SCSI Manager

In part 1 of this series of posts, Daniel suggested taking a look at the role the SCSI Manager plays in the Mac’s– and by extension, the Pippin’s– startup process. I took a break from examining the auth check code to dissect how the SCSI Manager behaves at startup on the Pippin, with the ultimate goal to discover if an exploit was even possible. After all, from my initial search of the ROM it’s clear that Apple had patched part of the boot process to only allow starting up from the internal CD-ROM drive– who’s to say there aren’t further patches deep in the SCSI code?

The tl;dr is that, after careful examination, I have determined that the SCSI code in the Pippin’s boot process is for the most part unchanged compared to a Mac of the same era. However I’m not yet sure if a “patch partition”-based exploit is possible.

Most of what follows I garnered from the “Monster Disk Driver Technote,” a mirror of which can be found here:

Every SCSI-equipped Mac for the most part follows the same procedure for booting from a SCSI device:

  1. It looks for a valid Driver Descriptor Map in the first 512-byte block
  2. Loads the device’s driver(s) according to the information found in the DDM
  3. Mounts the disk’s HFS partition
  4. Loads the boot blocks from the startup volume and executes them

This has been the case since SCSI was introduced to the Macintosh line with the Mac Plus in 1986. Previously, Macs had primarily booted from floppy disk and occasionally from a non-SCSI hard drive such as the HD20 or HyperDrive (but usually with help from a boot floppy). In either event, the Mac had no concept of drive “partitions” or even “volumes” in the modern sense– the MFS file system consumed the entire disk, and that was it.

The Apple Partition Map, introduced at the same time SCSI arrived on the Mac, changes this behavior by placing the primary file system in its own partition. On a high level, the Mac sees the volume as its own big disk, but the APM also allows device drivers to live in their own partitions rather than in INIT files as was done with the HD20. This moves their load time to much earlier in the boot process independent of the System Software and– critically– eschews the need for a separate boot disk. The SCSI code in ROM recognizes the presence of an APM, loads the driver(s) directly from disk, then locates and boots a startup volume. In this way, Macs can boot directly from a hard drive, a CD-ROM drive, or any SCSI-capable storage medium so long as it has the proper drivers preconfigured.

What does all of this have to do with the Pippin? Well, the Pippin’s only internal storage is its 128KB of non-volatile Flash memory, and even if the Pippin ROM was written to look there for an OS, 128KB is barely enough to boot the original Macintosh– never mind the System 7.5-based OS that Pippin titles shipped with. Instead, the Pippin boots from its internal (SCSI) CD-ROM drive, presumably calling into the SCSI Manager to load any device drivers followed by mounting the HFS partition, verifying the contents of the “PippinAuthenticationFile,” then continuing to boot the OS if everything checks out.

Wait a minute…

Before searching for an operating system, the SCSI Manager is supposed to load device drivers directly from disk according to the Driver Descriptor Map. It does a basic checksum verification, then… executes them! They run before the auth check!

At least, in theory.

I took a look at the “Pippin Network CD” (product ID BDB-002) that originally shipped with the 1.0 Atmark units in Japan. I chose this particular disc because of two things: 1) It has an Apple Partition Map and 2) It contains a very small device driver partition with plenty of extra room in which I could hack a “proof-of-concept.” I rustled out the original driver from an ISO image of the disc with a hex editor, then added some code that does the equivalent of while (!Button());. I then recalculated my hacked driver’s checksum using a quick program I wrote, poked the driver (and its proper checksum) back into the ISO, burned it to disc, booted my Pippin with it, and…

It booted directly to the login screen.

Pippin Network CD Version 1.0
I don’t know what any of this text says, but to me it just means disappointment.

This tells me that one of two things might be happening:

  1. The Pippin’s version of the SCSI Manager in ROM does not in fact load device drivers from disc. The SCSI Manager does a number of checks before it determines that it needs to load drivers for a particular device, and it’s possible that the Pippin fails one of those checks, possibly intentionally. In this case, it may be that the driver lives in ROM and any drivers on Pippin discs exist for the benefit of mounting on actual Macs, where the hardware isn’t fixed and device drivers would be more necessary. Also, only a handful of Pippin discs have partition maps; the majority of them are formatted as a flat HFS volume. What does the SCSI Manager do in that case? Where do the requisite device drivers come from?
  2. I screwed up hacking my driver code into the disc image before burning it. 😛

Unfortunately, when I mount this disc on my Power Mac G3 in Mac OS 9.2.2, my driver code doesn’t run there either. There must be some condition(s) under which the SCSI Manager will skip loading drivers from a CD-ROM mastered with them.

Looks like I have some more digging to do…

Exploring the Pippin ROM(s), part 3

Last week, I found the ‘rvpr’ 0 resource in the Pippin 1.0 ROM and the role it appears to play in the Pippin’s startup process. I noted that there are no ‘rvpr’ resources in the 1.2 or 1.3 ROMs, but after digging a little deeper I discovered that is only half true: the contents of ‘rvpr’ 0 are in fact present in both the 1.2 and 1.3 ROMs. But since there’s no entry for it in either ROM’s resource map, a call to _GetResource won’t find it. If 1.2 executes ‘rvpr’ 0 to perform the auth check, then the loading code I found last week must therefore be different in that version.

‘rvpr’ 0 itself appears to be a bit obfuscated. There are many subroutines contained within– if the Link / Unlk / Rts pattern is used as a heuristic, I counted over 250 of them. However, I suspect that much of this code is unused and/or intentional red herrings.

I quickly skimmed the code for an overall first impression before stepping through it in an editor. Some of the aforementioned subroutines are duplicates for some reason:

108A   4E56 0000    Link      A6, #$0
108E   2F2E 0008    Move.L    $8(A6), -(A7)
1092   206E 0008    MoveA.L   $8(A6), A0
1096   2068 0004    MoveA.L   $4(A0), A0
109A   2050         MoveA.L   (A0), A0
109C   4E90         Jsr       (A0)
109E   4E5E         Unlk      A6
10A0   4E75         Rts

10F0   4E56 0000    Link      A6, #$0
10F4   2F2E 0008    Move.L    $8(A6), -(A7)
10F8   206E 0008    MoveA.L   $8(A6), A0
10FC   2068 0004    MoveA.L   $4(A0), A0
1100   2050         MoveA.L   (A0), A0
1102   4E90         Jsr       (A0)
1104   4E5E         Unlk      A6
1106   4E75         Rts

1172   4E56 0000    Link      A6, #$0
1176   2F2E 0008    Move.L    $8(A6), -(A7)
117A   206E 0008    MoveA.L   $8(A6), A0
117E   2068 0004    MoveA.L   $4(A0), A0
1182   2050         MoveA.L   (A0), A0
1184   4E90         Jsr       (A0)
1186   4E5E         Unlk      A6
1188   4E75         Rts
27E8   4E56 0000    Link      A6, #$0
27EC   206E 0008    MoveA.L   $8(A6), A0
27F0   226E 000C    MoveA.L   $C(A6), A1
27F4   2290         Move.L    (A0), (A1)
27F6   7000         MoveQ.L   #$0, D0
27F8   4E5E         Unlk      A6
27FA   4E75         Rts

2AB0   4E56 0000    Link      A6, #$0
2AB4   206E 0008    MoveA.L   $8(A6), A0
2AB8   226E 000C    MoveA.L   $C(A6), A1
2ABC   2290         Move.L    (A0), (A1)
2ABE   7000         MoveQ.L   #$0, D0
2AC0   4E5E         Unlk      A6
2AC2   4E75         Rts

… while others are mostly duplicates with one or two extra instructions:

1C64   4E56 0000         Link      A6, #$0
1C68   206E 0008         MoveA.L   $8(A6), A0
1C6C   20AE 000C         Move.L    $C(A6), (A0)
1C70   216E 0010 0004    Move.L    $10(A6), $4(A0)
1C76   216E 0014 0008    Move.L    $14(A6), $8(A0)
1C7C   216E 0018 000C    Move.L    $18(A6), $C(A0)
1C82   216E 001C 0010    Move.L    $1C(A6), $10(A0)
1C88   216E 0020 0014    Move.L    $20(A6), $14(A0)
1C8E   216E 0024 0018    Move.L    $24(A6), $18(A0)
1C94   4E5E              Unlk      A6
1C96   4E75              Rts

27FC   4E56 0000         Link      A6, #$0
2800   206E 0008         MoveA.L   $8(A6), A0
2804   20AE 000C         Move.L    $C(A6), (A0)
2808   216E 0010 0004    Move.L    $10(A6), $4(A0)
280E   216E 0014 0008    Move.L    $14(A6), $8(A0)
2814   216E 0018 000C    Move.L    $18(A6), $C(A0)
281A   216E 001C 0010    Move.L    $1C(A6), $10(A0)
2820   4E5E              Unlk      A6
2822   4E75              Rts

2824   4E56 0000         Link      A6, #$0
2828   206E 0008         MoveA.L   $8(A6), A0
282C   20AE 000C         Move.L    $C(A6), (A0)
2830   216E 0010 0004    Move.L    $10(A6), $4(A0)
2836   216E 0014 0008    Move.L    $14(A6), $8(A0)
283C   216E 0018 000C    Move.L    $18(A6), $C(A0)
2842   216E 001C 0010    Move.L    $1C(A6), $10(A0)
2848   216E 0020 0014    Move.L    $20(A6), $14(A0)
284E   4E5E              Unlk      A6
2850   4E75              Rts

Some subroutines elicit from me a “WTF?!” reaction, like this implementation of memcmp:

A3C    8854 5F6D    DC.L      $88545F6D       ; ' T_m'
A40    656D 636D    DC.L      $656D636D       ; 'emcm'
A44    7000 0000    DC.L      $70000000       ; 'p   '
A48    4E56 0000    Link      A6, #$0
A4C    41EC 8226    Lea.L     -$7DDA(A4), A0
A50    2948 8390    Move.L    A0, -$7C70(A4)
A54    41EC 825E    Lea.L     -$7DA2(A4), A0
A58    2948 8394    Move.L    A0, -$7C6C(A4)
A5C    41EC 81F2    Lea.L     -$7E0E(A4), A0
A60    2948 8398    Move.L    A0, -$7C68(A4)
A64    42AC 839C    Clr.L     -$7C64(A4)
A68    4E5E         Unlk      A6
A6A    4E75         Rts

Once I sat down and walked through the code from the very top, though, things started to become a little clearer, although I’m not finished analyzing this code yet by any stretch. Recall from last week that the Pippin loads ‘rvpr’ 0 from ROM and then copies it into a block of memory allocated on the system heap. ‘rvpr’ 0 starts by getting its own address in the heap and applying an offset to it:

104    41FA FEFA         Lea.L     @start, A0
108    D1FC 0001 06A2    AddA.L    #$106A2, A0
10E    2008              Move.L    A0, D0
110    A055              _StripAddress
112    C18C              Exg.L     D0, A4

Next, it gets its address again, but without the offset:

14     41FA FFEA    Lea.L     @start, A0
18     2008         Move.L    A0, D0
1A     A055         _StripAddress

Then, it calls a subroutine that reads and writes to some data located at the offset -$7C60 from the address calculated in the first step, effectively placing it at $8A42 from the start of its memory block. It subtracts the longword found here (initially zero) from the unmodified start address, and if the result is zero, returns without doing anything else. But if it’s not zero, as would be the case when first running this code, things get interesting. It checks to see if _HWPriv is implemented and if so, sets a Boolean to true at offset $8A46. Then it passes its address + $8A47 to yet another subroutine. Finally, it sets $8A42 to the unmodified start address (effectively short-circuiting future calls), checks the Boolean at $8A46 and if it’s true, flushes the instruction cache by calling _HWPriv with selector 1 in register D0.

Hmmm. Why would it need to explicitly flush the instruction cache? The answer to that question lies in the subroutine that gets passed @start + $8A47. I haven’t fully wrapped my head around it yet, but from reading the code there it looks like offset $8A47 of ‘rvpr’ 0 looks to be a compressed list of offset locations, used to patch ‘rvpr’ 0 in place. A-ha! Now it’s clear why ‘rvpr’ 0 is copied to the system heap, and abundantly clear why the instruction cache needs to be flushed after this subroutine returns: it’s self-modifying code.

(P.S. Josh Juran graciously pointed out that the Metrowerks runtime used by e.g. CodeWarrior performs this same in-place relocation of code resources at runtime. Side question: What’s the possibility the Pippin’s auth check was written with CodeWarrior?)

Exploring the Pippin ROM(s), part 2

I’ve spent the last couple of evenings taking a closer look at the Pippin 1.0 ROM– specifically the boot process– trying to determine precisely how it verifies that a provided boot disc is in fact signed properly before passing it off to get loaded.

The earliest parts of the Pippin ROM are not much different from the late Quadra “universal” ROMs, which kind of makes sense given how close the Pippin is to the first couple generations of Power Macs. It deviates in a few places by writing to some areas of high memory for reasons I haven’t yet deduced, but is otherwise pretty straightforward compared to a real Mac– in accordance with being derived from a “universal” ROM, it retains the checks for various 68K processors and their capabilities, even despite only having the 68LC040 emulator underneath.

Where things start to get interesting is after the ROM initializes the SCSI Manager. It then looks for an ‘iNiT’ 1 resource (note the capitalization) and executes it, followed by an ‘iNiT’ resource named “Install XFS.” I haven’t yet dug into these segments to see what is happening here, but somehow I don’t think the latter block is installing drivers for a popular filesystem… 😉

Elliot Nunn pointed out to me that the boot process is part of the Start Manager and hadn’t changed much in the years leading up to the Pippin’s release. He also kindly suggested that I specifically search for FindStartupDevice.

So I did that.

I found a few interesting things.

FindStartupDevice pretty much follows the same steps as a real Mac… until we find valid boot blocks. Then it runs this little snippet of code:

1592   303C FFDC        Move      #-36, D0
1596   322A 0008        Move      dqRefNum(A2), D1
159A   B240             Cmp       D0, D1
159C   66C0             BNE.B     @TryAgain

-36 is the refNum for the internal CD-ROM drive. What this code does is check to see if our current drive queue entry is using the .AppleCD driver with the internal drive. If it’s not, it loops back to search for other potential boot volumes. Looks a bit like a hotfix and/or conditionally compiled to me (Why didn’t they just refactor the code so that it only searches the CD-ROM drive? Hey, I wasn’t there…), but essentially this means definitively that a 1.0 Pippin will not fully boot from any device other than its internal optical drive.

After this code is where things start to heat up. Take a look:

159E   2F3C FFFF FFFF   Move.L    #-1, -(A7)
15A4   4EBA 0B0A        Jsr       @mysterySub1          ; hmmm...
15A8   588F             AddQ.L    #4, A7
15AA   4EBA 1C84        Jsr       @mysterySub2          ; HMMM...
15AE   4A40             Tst       D0
15B0   6738             BEQ.B     @GotIt                ; success! boot!
15B2   303C FFDC        Move      #-36, D0
15B6   B06A 0008        Cmp       dqRefNum(A2), D0
15BA   66A2             BNE.B     @TryAgain
15BC   4FEF FFCE        Lea.L     -ioQElSize(A7), A7
15C0   204F             MoveA.L   A7, A0
15C2   317C FFDC 0018   Move      #-36, ioRefNum(A0)    ; .AppleCD
15C8   4268 0016        Clr       ioVRefNum(A0)
15CC   42A8 0012        Clr.L     ioNamePtr(A0)
15D0   317C 0007 001A   Move      #7, csCode(A0)        ; eject the disc
15D6   A004             _Control
15D8   3028 0010        Move      ioResult(A0), D0
15DC   4FEF 0032        Lea.L     ioQElSize(A7), A7
15E0   3F3C 0002        Move      #2, -(A7)             ; ShutDwnStart
15E4   A895             _ShutDown                       ; restart the Pippin
15E6   6000 FF76        Bra       @TryAgain
15EA   4A78 08D0        Tst       (CrsrState)
15EE   6B02             BMI.B     @ShowHappyMac
15F0   A852             _HideCursor

Immediately before making the decision to advance to the “Happy Mac” state (such as it is on the Pippin), this block of code passes -1 on the stack to a mystery subroutine. Then, it calls a second mystery subroutine, the result of which, if zero, indicates the Pippin is free and clear to boot from that volume (provided it’s the CD-ROM drive– again with that check!). If the check fails, the disc is ejected and the Pippin restarts.

So, let’s start with mysterySub1. mysterySub1 calls down to $20B0, where this happens:

20B0   60FF 000C AB0E    Bra.L     @mysterySub3

Hmmm. OK. So where does that take us? We end up in a short subroutine that loads a ‘nint’ 43 resource, then through a series of calls to _CodeFragmentDispatch we jump into InitAnimation. A-ha! ‘nint’ 43 starts with the string “Joy!peffpwpc” indicating that it’s PPC code, and a list of symbols at its end suggests it draws the “tray loading” animation using a loop of _DrawPicture and associated Color QuickDraw calls. Neat.

But mysterySub2 is where things get really juicy. Check it out:

3230   48E7 3030         MoveM.L   D2-D3/A2-A3, -(A7)
3234   2078 0DDC         MoveA.L   (BootGlobPtr), A0
3238   41E8 FF7E         Lea.L     -$82(A0), A0
323C   20B8 020C         Move.L    (Time), (A0)
3240   594F              SubQ      #4, A7
3242   2F3C 7276 7072    Move.L    #'rvpr', -(A7)       ; 'rvpr' resource
3248   4267              Clr       -(A7)                ; ID 0
324A   A9A0              _GetResource
324C   221F              Move.L    (A7)+, D1
324E   6700 0050         BEQ       @fail
3252   2041              MoveA.L   D1, A0
3254   2648              MoveA.L   A0, A3               ; A3 = handle to loaded 'rvpr' resource
3256   594F              SubQ      #4, A7
3258   2F08              Move.L    A0, -(A7)
325A   A9A5              _SizeRsrc
325C   201F              Move.L    (A7)+, D0
325E   2600              Move.L    D0, D3               ; D3 = size of loaded 'rvpr' resource
3260   A71E              _NewPtrSysClear
3262   6600 003C         BNE       @fail
3266   2F08              Move.L    A0, -(A7)
3268   2003              Move.L    D3, D0
326A   2248              MoveA.L   A0, A1
326C   204B              MoveA.L   A3, A0
326E   2050              MoveA.L   (A0), A0
3270   A02E              _BlockMove                     ; copy 'rvpr' resource into new ptr
3272   2F0B              Move.L    A3, -(A7)
3274   A9A3              _ReleaseResource
3276   2657              MoveA.L   (A7), A3             ; A3 -> our 'rvpr' resource data
3278   554F              SubQ      #2, A7
327A   3F2A 0008         Move      dqRefNum(A2), -(A7)
327E   3F2A 0006         Move      dqDrive(A2), -(A7)
3282   41FA FF5C         Lea.L     someData, A0
3286   2F08              Move.L    A0, -(A7)
3288   41FA FF46         Lea.L     someOtherData, A0
328C   2F10              Move.L    (A0), -(A7)
328E   4E93              Jsr       (A3)
3290   301F              Move      (A7)+, D0
3292   205F              MoveA.L   (A7)+, A0
3294   3F00              Move      D0, -(A7)
3296   A01F              _DisposePtr
3298   301F              Move      (A7)+, D0
329A   4CDF 0C0C         MoveM.L   (A7)+, D2-D3/A2-A3
329E   4E75              Rts
32A0   303C FFFF         Move      #-1, D0
32A4   60F4              Bra.B     @exit

That’s a bit to take in, but here’s a summary. We load ‘rvpr’ 0, then copy it into a new block of memory within the system heap. Then we pass the current DCE refNum, drive, a pointer to four longs (the first of which having the value $4B, or 75), and then a pointer to a much larger data block immediately preceding this subroutine to our local copy of ‘rvpr’ 0. It returns a 16-bit result code on the stack, which we save before disposing of our local copy of ‘rvpr’ 0, then we return. From examining what FindStartupDevice does earlier, the result of ‘rvpr’ 0 must be zero in order for the Pippin to complete the startup process.

So what’s in ‘rvpr’ 0?

'rvpr' 0 in 0xED
Anything stand out to you?

and… InitRSAAlgorithmChooser

That smells like paydirt to me, at least in the 1.0 ROM. The best part is that it’s written in 68K, my reading comprehension skills of which are much better than that of PowerPC assembly. Curiously, there are no ‘rvpr’ resources in ROMs 1.2 or 1.3, even though 1.2 also does the auth check. I’m interested in discovering what replaces it in 1.2, but for now I will continue to investigate 1.0’s implementation. Stay tuned. 🙂

Exploring the Pippin ROM(s)

The Pippin never really had a fair chance at life. Produced by Bandai under license to Apple, it was too expensive for a gaming console yet overshadowed in the computer market by full desktop machines. The system suffered a bit of an identity crisis as well: Was it for gaming? The Internet? Neither? Both? Pippin was one of those late-90s, pre-Jobs Apple experiments that didn’t take the world by storm and as such is largely ignored by retro gaming and computing enthusiasts.

Which is, of course, why I have one. 😀

Welcome to Pippin. ..that's OK, I didn't see it either.
Neither did most of the gaming world back then.

Essentially a Power Mac 6100/66 crammed into a set-top box, in my opinion the Pippin packs a bit more power than a lot of folks realize. The Pippin had the most success in Japan, and most titles developed for it were localized for that region. Unfortunately many of those titles were authored in Macromedia Director and did little to show off the capabilities of the console. There were a number of third parties lined up to develop English software for the system in 1996 and early 1997, but this was also the era of Nintendo 64 and PlayStation, so Pippin was cancelled before many of these titles would ever ship– in some cases even before projects got off the ground. One of those titles was Presto Studios’ The Journeyman Project: Pegasus Prime, which I’ve had and continue to enjoy the tremendous honor of maintaining a modern rerelease for Windows, macOS, and Linux. Pegasus Prime almost didn’t ship at all– that Pippin was based on the Macintosh platform allowed Bandai to publish it for Power Macs instead, where certainly the returns were more promising. A number of Pippin discs could run on Macs– this was in fact a hallmark of the system. But this could also go both ways– if Pippin software is also Mac software, then shouldn’t the reverse be true? Why isn’t there a homebrew scene for the Pippin?

Pegasus Prime on the Pippin
The rerelease is way better. Trust me. 😉

The only built-in software shipped with the Pippin came in the form of a circuit board with four megabytes of ROM that fit into a slot on the logic board inside the system’s case. The Pippin itself has no built-in operating system– each title shipped on one or more bootable CD-ROM discs containing a modified version of System 7.5.2. In a time before ubiquitous broadband Internet access like we have today, this allowed Bandai/Apple to provide upgrades and new features in software without having to download patches or release new hardware. But only titles that were signed or “Pippinized” by Apple could boot the system. This was done less to combat piracy (as the CDs themselves were and continue to be easily duplicated), but more to control the library, limiting the selection of titles to those produced by officially licensed developers. This is not that different from how Sony, Microsoft, and Nintendo prepare software for their respective consoles today. While the check for Pippinized discs could be skipped on test or retail kits using a special dongle provided by Apple (extremely hard to find today), development units came with a special ROM that removes the check entirely, allowing programmers to more conveniently test and debug multiple revisions before finally reaching “Gold Master” status and sending their final CDs off to be signed and pressed.

There were a couple different ROM board PCB styles– very early developers typically would get pre-production hardware with a ROM board populated with erasable Flash chips. These developers would periodically be asked to send their boards back to Apple to be reflashed with the latest ROM revision. Once the ROM was finalized and the Pippin went into production, boards shipped populated with mask ROM chips that could not be rewritten. I know of two developer ROMs, plus three ROM revisions that were released with retail consoles: 1.0 (white atMark Pippins in Japan), 1.2 (black @WORLD Pippins in the US and late atMarks), and 1.3 (very late Pippins). I have images of these three retail ROMs plus an image of the “GM Flash” developer ROM; I have never seen a retail ROM 1.1. As ROM 1.3 only shipped with a small number of Pippin units late in the system’s lifecycle, it is very rare but represents the last revision of the Pippin ROM, culminating a number of bug fixes and other changes.

ROM 1.3 also… I am told… removes the authentication check at boot, much like the developer ROMs do. 😉

I want to find out how. 😀

Pippin ROM board

Power Macs produced in 1998 or later boot from Open Firmware and tend to have their ROMs loaded from a file on disk and loaded into RAM– the “New World” model. Earlier Power Macs like the Pippin also boot from Open Firmware but still have a ROM burned into a physical chip or chips attached to the logic board– the “Old World” model. Open Firmware is contained within the last 1MB of these ROMs, and overall its job is to start the 68LC040 emulator and use it to boot the rest of the ROM, which is written predominantly in 68K. Thus, the first 3MB of an Old World ROM is straight 68K code, mostly comprising the Mac Toolbox APIs and some necessary drivers for booting the system and loading the OS from a startup device. These drivers can be found in what are known as “resources”– self-contained chunks of data addressed by a four-byte “type” and a two-byte ID (or occasionally a human-readable name as a Pascal string). Resources aren’t just segments of code– they can contain any type of data such as pictures, icons, sounds, and fonts, just to name a few.

I’m quite familiar with resources– my earliest work on Pegasus Prime involved reverse-engineering some custom resource formats developed to hold metadata about the game’s QuickTime-based animations. I did some work a number of months ago trying to reverse-engineer the MacWorks XL ROM for the Apple Lisa, in an effort to port the HD20-enabled .Sony driver to it so my Floppy Emu could boot it (One of these days I should revisit that and do a writeup about it, but that project is definitely on the backburner). In the course of dissecting that ROM, I learned a lot about the Mac boot process and how the ROM’s address space in general is laid out. For example, the first four bytes of a 68K Mac ROM consist of a checksum of the ROM’s contents. Four bytes at offset 4 provide a reset vector, which the Mac uses to boot. And, at offset $1A, four bytes provide an offset to where the ROM’s resources are stored. An easy first step to understanding a Mac ROM– or in this case, that of a Pippin– would be to extract its resources and examine them in a tool such as ResEdit.

I think one of the reasons why I couldn’t readily find a utility that took a binary ROM image and spit out a .rsrc file is that the way resources are stored in the ROM has changed since the earliest Macs. The Mac Plus ROM, for example, literally stores a resource map as one would find in an actual resource fork or .rsrc file– quite simple. By the time of the Pippin, though, this had changed to a slightly more complicated scheme. I spent a few hours last night successfully reverse-engineering this and then halfway through writing an extraction tool before the evening got too late. This evening, I was greeted by a pleasant surprise:

A few seconds later, I had the resources extracted from all four of my ROM images. I spent a little time tonight skimming through all I’ve found. A few highlights:

– The initials “kc” and the name “Kurt” are used for padding– these refer to Kurt Clark, presumably an engineer at Apple at the time.
– Open Firmware contains strings referencing TFTP in all the ROM revisions I have. Maybe the Pippin can boot from TFTP somehow, bypassing the authentication check?
– Gary Davidian’s 68LC040 emulator and Eric Traut’s dynarec can both be found after Open Firmware in the last 1MB of the ROM. Maybe they can be replaced with the versions found in Connectix’s Speed Doubler, saving the need for loading that INIT into RAM?
– All four ROMs contain the resources for the blinking ? and X floppy icons, as well as the recognizable Happy Mac. These icons are shown during the boot process on a real Mac but unused on the Pippin.
– There are two PPC-based ‘ndrv’ resources: .Display_Video_Apple_Control (to drive the “taos” graphics hardware) and .DAVInput, which might be used with the rear RCA audio jacks. The Pippin doesn’t have any video input capabilities, but the Power Mac 6100AV did… maybe .DAVInput and some of its associated hardware is borrowed from that machine?
– There are five 68K-based ‘DRVR’ resources– .rdrvr (for the internal 128KB of Flash storage), .AppleCD, .Sound, .Sony, .AppleSoundInput, and .EDisk. The latter two are a bit interesting– .AppleSoundInput because it’s either used for the rear audio jacks or the internal connection to the CD-ROM drive’s audio, and .EDisk because it suggests the existence of a ROM disk somewhere.
– The CD-ROM driver is identical between the GM Flash and 1.0 ROMs. But then there are major changes going into 1.2– in addition to code changes, a new drive model appears to be added to a whitelist: the Matshita CR-8006, a.k.a. the Apple CD 600e. But then, in 1.3, the whitelist reverts back to that of 1.0, while incorporating additional code changes. I’ve successfully got a Toshiba DVD-ROM drive to boot my @WORLD, so I’m not entirely sure what this whitelist is used for yet.

More to come as I dig deeper…