TrustZone Kernel Privilege Escalation (CVE-2016-2431)
In this blog post we’ll continue our journey from zero permissions to code execution in the TrustZone kernel. Having previously elevated our privileges to QSEE, we are left with the task of exploiting the TrustZone kernel itself.
“Why?”, I hear you ask. Well… There are quite a few interesting things we can do solely from the context of the TrustZone kernel. To name a few:
* We could hijack any QSEE application directly, thus exposing all of it’s internal secrets. For example, we could directly extract the stored real-life fingerprint or various secret encryption keys (more on this in the next blog post!).
* We could disable the hardware protections provided by the SoC’s XPUs, allowing us to read and write directly to all of the DRAM. This includes the memory used by the peripherals on the board (such as the modem).
* As we’ve previously seen, we could blow the QFuses responsible for various device features. In certain cases, this could allow us to unlock a locked bootloader (depending on how the lock is implemented).
So now that we’ve set the stage, let’s start by surveying the attack surface! […]