Apps Can Quickly Destroy Your Mobile’s Flash: Why They Don’t, and How to Keep It That Way Tao Zhang Aviad Zuck The University of North Carolina at Chapel Hill Technion – Israel Institute of Technology
[email protected] [email protected] Donald E. Porter Dan Tsafrir The University of North Carolina at Chapel Hill Technion – Israel Institute of Technology &
[email protected] VMware Research
[email protected] ABSTRACT 1 INTRODUCTION Although flash cells wear out, a typical SSD has enough cells andsuf- Smartphones typically include flash-based storage, because flash ficiently sophisticated firmware that its lifetime generally exceeds offers benefits such as fast random access, shock resistance, high the expected lifetime of its host system. Even under heavy use, SSDs density, and decreasing costs. A main drawback, however, is that last for years and can be replaced upon failure. On a smartphone, flash cells can tolerate only a limited number of writes (i.e., pro- in contrast, the hardware is more limited and we show that, under gram/erase cycles) before becoming unusable. Vendors therefore heavy use, one can easily, and more quickly, wear out smartphone apply various methods to increase the lifetime of flash packages [19, flash storage. Consequently, a simple, unprivileged, malicious ap- 41, 44, 48, 55, 59, 69, 84, 92, 93, 147], primarily by (1) provisioning plication can render a smartphone unbootable (“bricked”) in a few more physical than logical flash cells, and (2) using a sophisticated weeks with no warning signs to the user. This bleak result becomes firmware layer to spread the wear across these cells.