An information disclosure vulnerability exists on ARM implementations that use speculative execution in control flow via a side-channel analysis, aka "straight-line speculation." To exploit this vulnerability, an attacker with local privileges would need to run a specially crafted application. The security update addresses the vulnerability by bypassing the speculative execution.
What type of information could be disclosed by this vulnerability? The type of information that could be disclosed if an attacker successfully exploited this vulnerability is the contents of Kernel memory. An attacker could read the contents of Kernel memory from a user mode process.
Anthony Steinhauser, Google's Safeside project, https://github.com/google/safeside