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doc: TFC139-breakin written, Compal-unlock updated
author Mychaela Falconia <falcon@ivan.Harhan.ORG>
date Sun, 15 Nov 2015 03:47:19 +0000
parents
children 7a55a3eb985a
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974
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
diff changeset
1 Maliciously locked bootloader
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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2 =============================
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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3
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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4 When Compal (Motorola's ODM who designed and built their C1xx phones for them)
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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5 designed the firmware architecture and flash memory layout for their phones,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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6 they made a bad design decision by putting the boundary between their bootloader
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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7 and the main fw image at 0x2000, even though the flash erase block boundary
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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8 doesn't come until 0x10000 - thus every time the main fw needs to be reflashed
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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9 to a different version, the dangerous boot sector has to be reflashed too.
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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10
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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11 But then they made things even worse in the newer versions of their fw by
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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12 introducing a bootloader lock malfeature whereby the ability to interrupt boot
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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13 and load code serially may be artificially disabled. This malfeature is
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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14 implemented as follows:
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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15
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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16 * In the original firmware layout (before the addition of the malfeature in
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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17 question) the boot code occupies the flash range from 0 through 0x1FFF, then
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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diff changeset
18 there are some ID strings at 0x2000, 0x2020 and 0x2040, and then the part of
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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19 the firmware that used to be at 0x10000 in TI's reference fw starts at 0x20A0,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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20 with the entry point at 0x20F8 (corresponding to TI's 0x10058).
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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21
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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22 With the addition of the bootloader lock malfeature the 32-bit word at 0x2060
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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23 (previously unused and filled with 0xFFFFFFFF) became a control word telling
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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24 the bootloader whether diversion of the boot path to serial code download
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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25 should be allowed or not.
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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26
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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27 * When firmware images with this malfeature present are first built, the word
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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28 at 0x2060 contains 0xDDDDDDDD. (Does D stand for debug or development, or
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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29 was the developer who implemented this malfeature fascinated by large bra
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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30 cups? We may never know.) This word MUST read as 0xDDDDDDDD in order for
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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31 the boot code to allow serial download: if it reads as any other value (e.g.,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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32 if it contains 0xFFFFFFFF because only the 8192 byte boot code has been
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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diff changeset
33 programmed into flash sector 0, with blank flash from 0x2000 onward), no
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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34 serial download opportunity will ever be offered and the phone is effectively
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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35 bricked!
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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36
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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37 * For as long as the word at 0x2060 still contained 0xDDDDDDDD, Compal's
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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38 developers could continue gaining access through the bootloader and reflashing
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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39 their firmware. But when phones were to be shipped to customers with the
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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40 malicious bootloader lock activated, they probably sent some Test Mode command
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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41 (see RVTMUX write-up) to their running fw that caused it to write 0x00000000
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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42 into the flash word at 0x2060. (Remember that any bit in a NOR flash memory
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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43 can be programmed from 1 to 0 at any time in any combination, but changing
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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diff changeset
44 bits from 0 back to 1 is only possible with full sector erasure.)
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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45
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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46 * Once the word at 0x2060 has been programmed (in the flash memory sense) from
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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47 0xDDDDDDDD down to 0x00000000, the phone is irreversibly locked and has lost
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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48 its ability to ever run a different firmware version, like a kamikaze pilot's
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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49 plane that has discarded its landing gear and can only crash now.
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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50
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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51 TFC139 recovery
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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52 ===============
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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53
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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54 While it probably was Compal's, Motorola's and TracFone's intent that the
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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55 bootloader lock on their phones be truly irreversible, some genius out there
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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56 (we may never know who this person was/is) has found a way to recover the
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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57 reflashing capability on at least one very common flock of locked-down phones:
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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58 North American C139 units (1900+850 MHz hardware) sold with TracFone branding,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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59 firmware version 8.8.17. Here is how it goes:
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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60
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
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61 * Even though the bootloader is locked down, if one boots the full fw regularly,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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62 one can still access the RVTMUX interface which the TI-based fw implements
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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63 for debug trace and factory programming functions. One needs to key in the
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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64 magic sequence **16379# into the running fw, and a hidden menu will appear,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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65 giving the operator the option to enable trace. Selecting this option will
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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66 cause the fw to switch the headset jack to the UART carrying RVTMUX.
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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67
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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68 * Mot/Compal's firmware is based on a quite old version of TI's chipset
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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69 reference fw (relative to late TCS211 from the Openmoko/Pirelli era), and it
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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70 does not feature the Enhanced Test Mode (ETM) component with which we are
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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71 most familiar. However, it does implement the older set of non-enhanced
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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72 Test Mode commands, and these TM commands just happen to include raw memory
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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73 read and write operations at an arbitrary address. (For a while we were
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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74 under a mistaken belief that these commands were Compal's inventions, until
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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75 we discovered TI's original TM predating ETM.)
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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76
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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77 * The ingenious idea our hero came up with is that one can use the RVTMUX TM
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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78 memory write command to write a piece of "shellcode" into an unused RAM
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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79 location, and then use those very same memory write commands to cause a
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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80 transfer of control to this code by overwriting a function return address on
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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81 the stack!
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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82
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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83 * Once you can execute your own code on the Calypso, everything becomes possible
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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84 once again. At that point one can trivially reverse the bootloader lock by
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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85 erasing flash sector 0 and rewriting it with 0xDDDDDDDD in the 0x2060 word,
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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86 or even better, rewriting this boot sector with an older version of the boot
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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87 code that lacks the locking malfeature altogether.
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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88
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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89 In the FreeCalypso suite the tfc139 host utility performs the break-in using
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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90 the RVTMUX TM memory write and stack smashing method just described. The
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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91 "shellcode" injected by tfc139 re-enables the Calypso chip's own boot ROM and
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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92 jumps to it; this boot ROM will endlessly wait for a serial download because
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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93 the word at 0x2000 contains neither 0 nor 1 (it is part of an identifying ASCII
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
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94 string in Mot/Compal's fw), and the operator can then run fc-loadtool to
3f67d5bf96ef doc: TFC139-breakin written, Compal-unlock updated
Mychaela Falconia <falcon@ivan.Harhan.ORG>
parents:
diff changeset
95 perform arbitrary flash operations.