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More structure, spelling, clarification, images..

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Holger Hans Peter Freyther 2016-12-27 11:45:46 +01:00
parent c91fea6d73
commit 07e5c7d692
6 changed files with 61 additions and 31 deletions
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1
2016/33c3/.gitignore vendored
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@ -1,3 +1,4 @@
*.sw?
33c3-modems.html
images/upgrade_process.png
images/diag_frame.png

62
2016/33c3/33c3-modems.adoc
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@ -22,59 +22,66 @@ Dissecting modern (3G/4G) cellular modems
// 9 years of Osmocom?
// 3G and 4G development
// Hardware for decoding
* Implementing GSM specifications for the last decade (OpenMoko, Osmocom)
* Implementing GSM specifications for the last decade
* OpenMoko and then Osmocom
* 7 years since OsmocomBB for GSM
* In the past used and built devices using 2G modems
* Started to build 3G/4G software, logs/traces help
* Started to build 3G/4G software and logs/traces help
* Build tools to help understanding cellular technology
== History
image:images/sl6087_hw.png[height=280,role="gimmick_right"]
* OpenAT by Sierra Wireless
* 2G and 3G were available
* Write C code using OpenAT APIs
* Dynamically loaded into the RTOS
* Runs without privilege separation, MMU
* Eclipse based IDE and plugins (in clojure)
* Protocol to multiplex AT, log, debug
* 2G and 3G modems were available
* Discontinued HW platform => Locked in
* Various limitations
* Various other limitations
== Device requirements
* Get textual logging when handling messages
* Get a copy of the radio network messages and export to GSMTAP
* Get a copy of the radio network message and export to GSMTAP
* Like Tobias Engels https://github.com/2b-as/xgoldmon[x-goldmon]
* But for GPRS, 3G and 4G
* Enabled by default and not to be removed
* Enabled by default and not locked down in the future
== DIAG protocol
== Qualcomm DIAG protocol
* Qualcomm DIAG in many products (DVB-H, GSM, ...)
* https://events.ccc.de/congress/2011/Fahrplan/attachments/2022_11-ccc-qcombbdbg.pdf[Presented] by Guillaume Delugre at 28C3
* Simple HDLC frame (0x7e), cmd, data, CRC16
* Thousands of different message structures
* Events, Logging, Command/Response
* ModemManager, gsm-parser consume only a small fraction
image:images/diag_frame.png[width="90%"]
* Qualcomm diag in many products (see Guillaume Delugres https://events.ccc.de/congress/2011/Fahrplan/attachments/2022_11-ccc-qcombbdbg.pdf[talk] at 28C3)
* HDLC frame, CRC16, simple framing (0x7e)
* Command, Response, Events
** Enable logging of subsystems
** Enable events for subsystems
** Trigger firmware upgrade
** Read/Write RAM
* ModemManager uses it for additional information
* gsmparser of snoopsnitch to export to GSMTAP
== Selecting a device
image:images/28c3_option_stick.png[width="30%",role="gimmick_right"]
* 3G Options Icon stick exposes DIAG out of the box
* Quectel UC20 (2G+3G) enable it by default
* Quectel EC20 (2G+3G+4G) enable it by default
* 2G, 3G and 4G sounds quite nice
* EC20 comes as mini-PCIe module as well
== Quectel EC20
image:images/ec20.png[height=200,role="gimmick_right"]
* Using a Qualcomm MDM 9615 chipset
* Uses a Qualcomm MDM 9615 chipset
* Also used in the iPhone5
* Surprisingly runs Linux
* In our case surprisingly runs Linux
* Not surprising to people familiar with MDM9615 (e.g https://media.defcon.org/DEF%20CON%2023/DEF%20CON%2023%20presentations/DEFCON-23-Mickey-Shkatov-Jesse-Michael-Scared-poopless-LTE-and-your-laptop-UPDATED.pdf[Mickey Shkatov])
* Not a lot of documentation available
@ -88,7 +95,7 @@ image:images/ec20.png[height=200,role="gimmick_right"]
== GPL compliance
* Got a firmware upgrade to fix stability
* Might contain traces of Linux?
* Looks like it contains traces of Linux?
* No written offer, let's see if it runs Linux
* gpl-tools to unpack unyaffs
* strings, etc., AT+QLINUXCMD=?
@ -97,7 +104,7 @@ image:images/ec20.png[height=200,role="gimmick_right"]
== GPL compliance
* Linux basis created by Qualcomm used by Quectel
* Linux basis created by Qualcomm and used by Quectel
* https://wiki.codeaurora.org/xwiki/bin/QLBEP/
* Many branches, releases, which to use?
@ -252,9 +259,9 @@ image:images/gandroid_logo.png[height=200,role="gimmick_right"]
image:images/redbend.png[height=76,role="gimmick_right"]
* Based on the recovery.git code
* But for some reason (legacy?) is using RedBend
* RSA linked into the binary but not called
* RedBend used by many more companies and systems (e.g. Quectel UC20)
* But for some reason using RedBend for the update (legacy?)
* RSA still linked into the binary but not used
* RedBend used by many more companies and systems (e.g. Quectel UC20, automotive)
== RedBend (delta update) software
@ -262,7 +269,8 @@ image:images/redbend.png[height=76,role="gimmick_right"]
* Used in OMA DeviceManagement? (e.g. https://www.blackhat.com/docs/us-14/materials/us-14-Solnik-Cellular-Exploitation-On-A-Global-Scale-The-Rise-And-Fall-Of-The-Control-Protocol.pdf[Solnik])
* Lots of starring at hexdumps, lots of help from Dieter Spaar
* Binary file format to diff, inserts, remove, link files
* Variable size Table Of Contents
* Can update images/mtd partitions too
* Variable sized LZMAed Table Of Contents
** Filenames separated with 0x00
** Permissions separated with 0xAF
** Sections for diff, inserts with crc32, filesize, permission
@ -296,10 +304,8 @@ Start download fota for update.zip
image:images/upgrade_process.png[]
== Firmware example
* Show it?
* Applies what ever was downloaded...
* Assumes no MITM is possible
== Recommedation

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2016/33c3/Makefile
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@ -4,5 +4,8 @@ all: 33c3-modems.html
images/upgrade_process.png: images/upgrade_process.blockdiag
blockdiag -a -o images/upgrade_process.png images/upgrade_process.blockdiag
33c3-modems.html: 33c3-modems.adoc 33c3-modems.css images/upgrade_process.png
images/diag_frame.png: images/diag_frame.blockdiag
blockdiag -a -o images/diag_frame.png images/diag_frame.blockdiag
33c3-modems.html: 33c3-modems.adoc 33c3-modems.css images/upgrade_process.png images/diag_frame.png
asciidoc -a stylesheet=$(PWD)/33c3-modems.css 33c3-modems.adoc

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blockdiag {
node_height = 100;
span_width = 2;
default_fontsize = 16;
START [label="0x7E"];
CMD [label="CMD"];
DAT [label="Payload", width=300];
CRC [label="CRC16"];
END [label="0x7E"];
START -> CMD [style = none];
CMD -> DAT [style = none];
DAT -> CRC [style = none];
CRC -> END [style = none];
}

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2016/33c3/images/upgrade_process.blockdiag
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blockdiag {
node_width = 200;
default_group_color = none;
AT [label="atfwd_daemon"];
QC [label="QCMAP_ConnectionManager"];
WG [label="wget"];
RI [label="recovery image"];
AT -> QC;
AT -> WG -> RI;
AT -> QC [label="start"];
AT -> WG [label="start"];
AT -> RI [label="reboot"];
group { WG; RI };
}