[Replicant] [PATCH 9/9] freedom-privacy-security-issues: Improve the modem isolation description.

[Denis 'GNUtoo' Carikli]

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo at no-log.org>
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 freedom-privacy-security-issues.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/freedom-privacy-security-issues.php b/freedom-privacy-security-issues.php
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--- a/freedom-privacy-security-issues.php
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 			<h3>The current situation of freedom and privacy/security on mobile devices</h3>
 			<p>A mobile device respecting the users' freedom would have:<ul><li>Free hardware</li><li>Free firmwares</li><li>Free modem system</li><li>Free bootrom and bootloader</li><li>Free system and applications</li></ul>Regarding <a href="#free-hardware">free hardware</a>, it barely exist as of today. The ways of modifying existing hardware are very limited. Because of that, new versions of the hardware have to be produced to carry the modifications, and this is expensive. While producing printed circuit boards (PCBs) costs a lot of money, producing integrated circuits is out of reach. A few devices come with schematics, or full design files for the PCB, but that's usually as far as it gets. Hence, totally-free hardware doesn't exist yet. While design for FPGAs do exist in free software licenses, FPGAs are not practical enough to be used to replace ASICs in smartphones, and most of them even proprietary software tools.</p>
 			<p>Firmwares running inside integrated circuits are most of the time proprietary. While free firmwares are hard to write, some exist for very specific hardware (e.g. <a href="//www.arduino.cc/">Arduino</a>, <a href="//dangerousprototypes.com/docs/Bus_Pirate">Bus Pirate</a>) and sometimes,  manufacturers can liberate firmwares running in their integrated circuits (e.g. <a href="//github.com/qca/open-ath9k-htc-firmware">ath9k_htc</a>). However, it is not always possible to even replace those firmwares: some are loaded to the integrated circuit by the main CPU but some others reside in separate storage that is loaded by that integrated circuit. In that case, we wound't be able to tell the difference with an integrated circuit lacking any storage. With seperate storage, the firmware cannot easily be updated to a free replacement.</p>
-			<p><a href="images/freedom-privacy-security-issues/bad-modem-isolation.png" data-lightbox="current-situation" data-title="Bad modem isolation"><img src="images/freedom-privacy-security-issues/bad-modem-isolation.png" alt="Bad modem isolation" style="width: 250px; float: left;"/></a>The modem system on telephony-enabled mobile devices is always proprietary. While <a href="//bb.osmocom.org/">OsmocomBB</a>, a free software GSM stack exists, it only runs on some old feature phones or or the openmoko smartphones modem. It currently requires a host computer to operate and is not certified to run on public networks. Despite this situation, the modem remains a crucial part for privacy/security: it is nearly always connected to the GSM network, allowing for <a href="//www.gnu.org/philosophy/malware-mobiles.html">remote control</a>. The modem can be more or less damaging to privacy/security depending on what hardware it has access to and can control. That is to say, how isolated it
  is from
  the rest of the device.<br /><br />A device with bad modem isolation would allow the modem to access and control key parts of the hardware, such as the RAM, storage, GPS, camera, user I/O and microphone. This situation is terrible for privacy/security as it provides plenty of ways to efficiently spy on the user, triggered remotely over the mobile telephony network. Those are accessible to the mobile telephony operator, but also to attackers setting up fake base stations for that purpose. <a href="images/freedom-privacy-security-issues/good-modem-isolation.png" data-lightbox="current-situation" data-title="Good modem isolation"><img src="images/freedom-privacy-security-issues/good-modem-isolation.png" alt="Good modem isolation" style="width: 250px; float: right;"/></a>On the other hand, when the modem is well-isolated from the rest of the device, it is limited to communicating directly with the SoC and can only access the device's microphone when allowed by the SoC. It is th
 en stric
 tly limited to accessing what it really needs, which considerably reduces its opportunities to spy on the user. While it doesn't solve any of the freedom issues, having an isolated modem is a big step forward for privacy/security. However, it is nearly impossible to be entirely sure that the modem is actually isolated, as any documentation about the device cannot be trusted, due to the lack of effective hardware freedom. On the other hand, it is possible to know that the modem is not isolated, when there is proof that it can access hardware that could be used to spy on the user.</p>
+			<p><a href="images/freedom-privacy-security-issues/bad-modem-isolation.png" data-lightbox="current-situation" data-title="Bad modem isolation"><img src="images/freedom-privacy-security-issues/bad-modem-isolation.png" alt="Bad modem isolation" style="width: 250px; float: left;"/></a>The modem system on telephony-enabled mobile devices is always proprietary. While <a href="//bb.osmocom.org/">OsmocomBB</a>, a free software GSM stack exists, it only runs on some old feature phones or or the openmoko smartphones modem. It currently requires a host computer to operate and is not certified to run on public networks. Despite this situation, the modem remains a crucial part for privacy/security: it is nearly always connected to the GSM network, allowing for <a href="//www.gnu.org/philosophy/malware-mobiles.html">remote control</a>. The modem can be more or less damaging to privacy/security depending on what hardware it has access to and can control. That is to say, how isolated it
  is from
  the rest of the device.<br /><br />A device with bad modem isolation cannot prevent the modem from accessing and controling key parts of the hardware. For instance the main CPU's RAM, its storage, the GPS, the camera, user I/O and the microphone. This situation is terrible for privacy/security as it provides plenty of opportunities to efficiently spy on the user, that could be triggered remotely over the mobile telephony network. That mobile telephony network is accessible to the mobile telephony operator, but also to attackers setting up fake base stations for that purpose. <a href="images/freedom-privacy-security-issues/good-modem-isolation.png" data-lightbox="current-situation" data-title="Good modem isolation"><img src="images/freedom-privacy-security-issues/good-modem-isolation.png" alt="Good modem isolation" style="width: 250px; float: right;"/></a>On the other hand, when the modem is well-isolated from the rest of the device, it is limited to communicating directly w
 ith the 
 SoC and can only access the device's microphone when allowed by the SoC. It is then strictly limited to accessing what it really needs, which considerably reduces its opportunities to spy on the user. While it doesn't solve any of the freedom issues, having an isolated modem is a big step forward for privacy/security. However, it is nearly impossible to be entirely sure that the modem is actually isolated, as any documentation about the device cannot be trusted, due to the lack of effective hardware freedom. On the other hand, it is possible to know that the modem is not isolated, when there is proof that it can access hardware that could be used to spy on the user.</p>
 			<p>Looking at the software that runs early on the SoC, the first component is the bootrom. It is always proprietary and is stored in read-only memory, so it cannot be changed (in that case, it almost seems to behave like hardware). However, regarding the bootloader, the situation is different for each platform. There are actually multiple stages of bootloaders, some of which can be free. However, it also occurs that the bootloaders are cryptographically signed with a private key. In that case, the bootrom will check the signature against a public key that cannot be replaced and only run the bootloader if the signature matches. That sort of tivoization prevents replacing pre-installed bootloaders, even when their sources are released as free software. There are some good platforms that don't perform such signature checks and can run free bootloaders (e.g. Allwinner Ax, TI OMAP General-Purpose).</p>
 			<p><a href="images/freedom-privacy-security-issues/operating-system.png" data-lightbox="current-situation" data-title="Mobile operating system"><img src="images/freedom-privacy-security-issues/operating-system.png" alt="Mobile operating system" style="width: 250px; float: left;"/></a>The biggest part of the software running on a mobile device is the operating system, that runs on the main CPU. It has access to most integrated circuits (I/O, camera, microphone, GPS, etc) as well as the user's data and communications. It is the most critical part for privacy/security and is also very important for free software as it interacts with the user directly and holds knowledge about communication with the hardware. Many mobile operating systems are mostly free software (e.g. <a href="//www.android.com/">Android</a>, <a href="//mozilla.org/firefox/os">Firefox OS</a>, <a href="//ubuntu.com/phone">Ubuntu Touch</a>, <a href="//www.tizen.org/">Tizen</a>), as they use the <a href="//www.
 kernel.o
 rg/">Linux kernel</a>, a free framework and ship with free base applications. However, the user-space hardware abstraction layers are for the most part proprietary (it varies from one device to another) and they also ship with proprietary loaded firmwares for various integrated circuits. Every piece of proprietary software running on the system is a risk for privacy/security as they can offer <a href="//www.gnu.org/philosophy/malware-mobiles.html">remote access back-doors</a> and compromise the rest of the system.<br />None of these mostly-free systems have a clear policy to reject proprietary software and not advocate its use, except for Replicant.</p>
 			<p>While the operating system is a very important piece of software, it doesn't ship with applications that cover the wide spectrum of activities that a mobile device is expected to provide. Thankfully, plenty of free software applications exist for each kind of (mostly-)free operating system, sometimes gathered in free software application stores (such as <a href="//www.f-droid.org/">F-Droid</a> for Android systems).</p>
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