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Pirelli: documented and verified the checksum scheme used for the factory block
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 25 Dec 2016 23:48:16 +0000
parents 10a9a0ca9d07
children
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10a9a0ca9d07 objgrep/README written
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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1 We have TI's reference firmware for the Calypso/Iota/Rita chipset (Leonardo) in
10a9a0ca9d07 objgrep/README written
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2 the form of linkable COFF objects and some source pieces, but when it comes to
10a9a0ca9d07 objgrep/README written
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3 practically usable "dumbphones" based on this chipset, we only have the binary
10a9a0ca9d07 objgrep/README written
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4 fw images read out of flash, without any kind of symbolic info.
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5
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6 The tools in this directory perform a kind of grep operation, searching an
10a9a0ca9d07 objgrep/README written
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7 unknown binary fw image for the bits of code or data contained in a linkable
10a9a0ca9d07 objgrep/README written
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8 COFF object. The objective was to determine whether or not our "reference"
10a9a0ca9d07 objgrep/README written
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9 Leonardo objects could be found verbatim in the set of proprietary firmwares
10a9a0ca9d07 objgrep/README written
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10 from Compal and Foxconn (Pirelli DP-L10) that run on our "dumbphone" targets.
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11
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12 The tools are as follows:
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13
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14 objgrep
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15
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16 This tool extracts one section (e.g., .text or .const, to be specified
10a9a0ca9d07 objgrep/README written
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17 on the command line) from a "needle" COFF object and searches for it in
10a9a0ca9d07 objgrep/README written
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18 the "haystack" unknown binary. The byte positions in the sought-for
10a9a0ca9d07 objgrep/README written
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19 object section where relocs are to be applied at linking time are masked
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20 as appopriate for each reloc type, and the section is expected to start
10a9a0ca9d07 objgrep/README written
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21 on a 4-byte-aligned boundary in the unknown binary. If a match is
10a9a0ca9d07 objgrep/README written
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22 found, objgrep can print out the list of symbol addresses in the
10a9a0ca9d07 objgrep/README written
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23 sought-for and found section, and it can also deduce some symbols
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24 external to the module or belonging to the module's other sections by
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25 looking where the relocs that were masked for the match point to in the
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26 unknown binary.
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27
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28 In order for this form of grep to be effective, the section being
10a9a0ca9d07 objgrep/README written
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29 searched for should be "meaty", i.e., mostly code or constant data with
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30 some interspersed relocs. If the sought-for section is very small, fits
10a9a0ca9d07 objgrep/README written
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31 the same pattern after reloc masking as other unrelated bits of code,
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32 or consists mostly of relocs, the most likely result will be a useless
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33 false hit.
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34
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35 objgrep-fe
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36
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37 This program is a front-end to objgrep. It reads a line-based text file
10a9a0ca9d07 objgrep/README written
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38 listing the objects and sections to be grepped for, and invokes objgrep
10a9a0ca9d07 objgrep/README written
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39 for each listed section. The output of objgrep is captured through a
10a9a0ca9d07 objgrep/README written
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40 pipe; objgrep-fe collates together the symbol addresses found with each
10a9a0ca9d07 objgrep/README written
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41 individual objgrep hit and produces a sorted symbol listing.
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42
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43 Results
10a9a0ca9d07 objgrep/README written
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44 =======
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45
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46 The idea proved quite successful in the case of Pirelli DP-L10 firmware,
10a9a0ca9d07 objgrep/README written
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47 specifically version D910.0.3.98: this fw appears to have been built with
10a9a0ca9d07 objgrep/README written
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48 exactly the same RTS, Nucleus and GPF libraries that are featured in our
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49 Leonardo semi-src as "very stable blobs", i.e., *.lib files in the source tree
10a9a0ca9d07 objgrep/README written
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50 itself, rather than blobs under g23m/__out__ for which TI's closed source
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51 police excluded the corresponding source. Every object that comes from these
10a9a0ca9d07 objgrep/README written
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52 libraries in our leo2moko build was also found in Pirelli's fw.
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53
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54 It is worth noting that the GPF libraries in particular contain a few objects
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55 with embedded second-granularity timestamps, courtesy of the C compiler's
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56 __DATE__ and __TIME__ preprocessor definitions, i.e., the timestamp strings
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57 with times to the second are emitted into the code image built with these
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58 libraries. These timestamped objects were found in Pirelli's fw with our
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59 objgrep tools along with the rest of GPF, proving beyond any doubt that this fw
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60 has been built with exactly the same GPF libs as our leo2moko.
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61
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62 This confirmation in the case of Pirelli's fw is very reassuring because this
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63 fw has received a lot of real-life testing: I've been using a Pirelli running
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64 its original proprietary fw (as no free fw exists yet, for this or any other
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65 dumbphone) as my personal everyday cellphone for over a year now. That is a
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66 lot more real life experience than I can get with anything Openmoko-based, and
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67 it is reassuring to know that the GPF libraries we have painstakingly
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68 reconstructed are used not only in the largely-untested moko firmware, but also
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69 in the much more real-life-tested Pirelli DP-L10 fw.
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70
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71 Attemping the same grep against Compal's fw yielded far fewer hits, however.
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72 A lot of RTS modules were found, but very little from Nucleus or GPF libs.
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73 Nucleus' tct and tmt assembly modules were found, but not much else. Manual
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74 examination of Compal's INC_Initialize() function (which is easy to locate even
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75 in a totally unknown fw binary, as it's only one ARM->Thumb call veneer away
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76 from the boilerplate code at the boot entry point) has revealed that it's the
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77 same code, but compiled slightly differently, probably a slightly newer C
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78 compiler version. (The version in our reference libs saves one more call-
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79 preserved register than necessary; the version that appears in Compal's fw is
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80 fully optimal in this regard.) I reason that the same compiler difference must
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81 be responsible for the great scarcity of hits in general, as these kinds of
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82 compiler changes would produce differences in just about every module.