page.title=Security Enhancements in Android 1.5 through 4.1
@jd:body

<p>
Android provides a multi-layered security model described in the <a href="{@docRoot}security/index.html">Android
Security Overview</a>. Each update to Android includes dozens of
security enhancements to protect users.  The following are some of the security
enhancements introduced in Android versions 1.5 through 4.1:</p>

<dl>
<dt><strong>Android 1.5</strong></dt>
<dd><ul>
<li>ProPolice to prevent stack buffer overruns (-fstack-protector)</li>
<li>safe_iop to reduce integer overflows</li>
<li>Extensions to OpenBSD dlmalloc to prevent double free() vulnerabilities and
to prevent chunk consolidation attacks.  Chunk consolidation attacks are a
common way to exploit heap corruption.</li>
<li>OpenBSD calloc to prevent integer overflows during memory allocation</li>
</ul>
</dd>

<dt><strong>Android 2.3</strong></dt>
<dd><ul>
<li>Format string vulnerability protections (-Wformat-security -Werror=format-security)</li>
<li>Hardware-based No eXecute (NX) to prevent code execution on the stack and heap</li>
<li>Linux mmap_min_addr to mitigate null pointer dereference privilege
escalation (further enhanced in Android 4.1)</li>
</ul>
</dd>

<dt><strong>Android 4.0</strong></dt>
<dd>Address Space Layout Randomization (ASLR) to randomize key locations in memory
</dd>

<dt><strong>Android 4.1</strong></dt>
<dd><ul>
<li>PIE (Position Independent Executable) support</li>
<li>Read-only relocations / immediate binding (-Wl,-z,relro -Wl,-z,now)</li>
<li>dmesg_restrict enabled (avoid leaking kernel addresses)</li>
<li>kptr_restrict enabled (avoid leaking kernel addresses)</li>
</ul>
</dd>

</dl>