en/devices/tech/config/kernel.html

page.title=Kernel Configuration
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    <h2>In this document</h2>
    <ol id="auto-toc">
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<p>Use the following configuration settings as a base for an Android kernel
configuration. Settings are organized into <code>android-base</code> and
<code>android-recommended</code> .cfg files:

<ul>
<li><code>android-base</code>. These options enable core Android features and
should be enabled by all devices.</li>

<li><code>android-recommended</code>. These options enable advanced Android
features and are optional for devices.</li>
</ul>

<p>Both the android-base.cfg and android-recommended.cfg files are located in
the android-common kernel repo at
<a href="https://android.googlesource.com/kernel/common/">https://android.googlesource.com/kernel/common/</a>.
<p>In version 4.8 of the upstream Linux kernel, a new location (kernel/configs)
was designated for kernel configuration fragments. The android base and
recommended config fragments are located in that directory for branches based on
4.8 or later. For kernel branches based on releases prior to 4.8, the config
fragments are located in the android/ directory.</p>

<p>For details on controls already undertaken to strengthen the kernel on your
devices, see <a href="{@docRoot}security/overview/kernel-security.html">System
and Kernel Security</a>. For details on required settings, see the
<a href="{@docRoot}compatibility/cdd.html">Android Compatibility Definition
Document (CDD)</a>.</p>

<h2 id="generating">Generating kernel config</h2>
<p>For devices that have a minimalist defconfig, you can use the following to
enable options:</p>

<pre><code>ARCH=<em>arch</em> scripts/kconfig/merge_config.sh <em>path</em>/<em>device</em>_defconfig android/configs/android-base.cfg android/configs/android-recommended.cfg</code></pre>

<p>This generates a .config file you can use to save a new defconfig or
compile a new kernel with Android features enabled.</p>

<h2 id="usb">Enabling USB host mode options</h2>

<p>For USB host mode audio, enable the following options:</p>
<pre><code>CONFIG_SND_USB=y
CONFIG_SND_USB_AUDIO=y
# CONFIG_USB_AUDIO is for a peripheral mode (gadget) driver
</code></pre>

<p>For USB host mode MIDI, enable the following option:</p>
<pre><code>CONFIG_SND_USB_MIDI=y</code></pre>

<h2 id="Seccomp-BPF-TSYNC">Seccomp-BPF with TSYNC</h2>
<p>Seccomp-BPF is a kernel security technology that enables the creation of
sandboxes to restrict the system calls a process is allowed to make. The TSYNC
feature enables the use of Seccomp-BPF from multithreaded programs. This ability
is limited to architectures that have seccomp support upstream: ARM, ARM64, x86,
and x86_64.</p>

<h3 id="backport-ARM-32">Backporting for Kernel 3.10 for ARM-32, X86, X86_64</h3>

<p>Ensure that <code>CONFIG_SECCOMP_FILTER=y</code> is enabled in the Kconfig
(verified as of the Android 5.0 CTS), then cherry-pick the following changes
from the AOSP kernel/common:android-3.10 repository: <a href="https://android.
googlesource.com/kernel/common/+log/9499cd23f9d05ba159
fac6d55dc35a7f49f9ce76..a9ba4285aa5722a3b4d84888e78ba8adc0046b28">9499cd23f9d05ba159fac6d55dc35a7f49f9ce76..a9ba4285aa5722a3b4d84888e78ba8adc0046b28</a>
</p>

<ul>
<li><a href="https://android.googlesource.com/kernel/common/+/a03a2426ea9f1d9dada33cf4a824f63e8f916c9d">a03
a242 arch: Introduce smp_load_acquire(), smp_store_release()</a> by Peter
Zijlstra</li>
<li><a href="https://android.googlesource.com/kernel/common/+/987a0f1102321853565c4bfecde6a5a58ac6db11">987a0f
1 introduce for_each_thread() to replace the buggy while_each_thread()</a> by
 Oleg Nesterov</li>
 <li><a href="https://android.googlesource.com/kernel/common/+/2a30a4386e4a7e1283157c4cf4cfcc0306b22ac8">2a30a43
seccomp: create internal mode-setting function</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+
/b8a9cff6dbe9cfddbb4d17e2dea496e523544687">b8a9cff
seccomp: extract check/assign mode helpers</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/8908dde5a7fdca974374b0dbe6dfb10f69df7216">8908dde
seccomp: split mode setting routines</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/e985fd474debedb269fba27006eda50d0b6f07ef">e985fd4  seccomp: add
"seccomp" syscall</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/9d0ff
694bc22fb458acb763811a677696c60725b">9d0ff69
sched: move no_new_privs into new atomic flags</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/b6a12bf4dd762236c7f637b19cfe10a268304b9b">b6a12bf
seccomp: split filter prep from check and apply</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/61b6b882a0abfeb627d25a069cfa1d232b84c8eb">61b6b88
seccomp: introduce writer locking</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/c852ef778224ecf5fe995d74ad96087038778bca">c852ef7
seccomp: allow mode setting across threads</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/f14a5db2398afed8f416d244e6da6b23940997c6">f14a5db
seccomp: implement SECCOMP_FILTER_FLAG_TSYNC</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/9ac860041db
860a59bfd6ac82b31d6b6f76ebb52">9ac8600
seccomp: Replace BUG(!spin_is_locked()) with assert_spin_lock</a> by Guenter
Roeck</li>
<li><a href="https://android.googlesource.com/kernel/common/+/900e9fd0d5d15c596cacfb89ce007c933cea6e1c">900e9fd
seccomp: fix syscall numbers for x86 and x86_64</a> by Lee Campbell</li>
<li><a href="https://android.googlesource.com/kernel/common/+/a9ba4285aa5722a3b4d84888e78ba8adc0046b28">a9ba428
ARM: add seccomp syscall</a> by Kees Cook</li>
</ul>

<h3 id="backport-ARM-64">Backporting for Kernel 3.10 for ARM-64</h3>
<p>Ensure <code>CONFIG_SECCOMP_FILTER=y</code> is enabled in the Kconfig
(verified as of the Android 5.0 CTS), then cherry-pick the following changes
from the AOSP kernel/common:android-3.10 repository:</p>
<ul>
<li><a href="https://android.googlesource.com/kernel/common/+/cfc7e99e9e3900056028a7d90072e9ea0d886f8d">cfc7e99e9
arm64: Add __NR_* definitions for compat syscalls</a> by JP Abgrall</li>
<li><a href="https://android.googlesource.com/kernel/common/+/bf11863d45eb3dac0d0cf1f818ded11ade6e28d3">bf11863
arm64: Add audit support</a> by AKASHI Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/3
e21c0bb663a23436e0eb3f61860d4fedc233bab">3e21c0b
arm64: audit: Add audit hook in syscall_trace_enter/exit()</a> by JP Abgrall</li>
<li><a href="https://android.googlesource.com/kernel
/common/+/9499cd23f9d05ba159fac6d55dc35a7f49f9ce76">9499cd2
syscall_get_arch: remove useless function arguments</a> by Eric Paris</li>
<li><a href="https://android.googlesource.com/kernel/common/+/2a30a4386e4a7e1283157c4cf4cfcc0306b22ac8">2a30a43
seccomp: create internal mode-setting function</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/b8a9cff6dbe9cfddbb4d17e2dea496e523544687">b8a9
cff  seccomp: extract check/assign mode helpers</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/8908dde5a7fdca974374b0dbe6dfb10f69df7216">8908dde
seccomp: split mode setting routines</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/e985fd474debedb269fba27006eda50d0b6f07ef">e985fd4
seccomp: add "seccomp" syscall</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/9d0ff694bc22fb458acb763811a677696c60725b">9d0ff69
sched: move no_new_privs into new atomic flags</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/b6a12bf4dd762236c7f637b19cfe10a268304b9b">b6a12bf
seccomp: split filter prep from check and apply</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/61b6b882a0abfeb627d25a069cfa1d232b84c8eb">61b6b88
seccomp: introduce writer locking</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/c852ef778224ecf5fe995d74ad96087038778bca">c852ef7
seccomp: allow mode setting across threads</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/f14a5db2398afed8f416d244e6da6b23940997c6">f14a5db
seccomp: implement SECCOMP_FILTER_FLAG_TSYNC</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/9ac860041db860a59bfd6ac82b31d6b6f76ebb52">9ac8600
seccomp: Replace BUG(!spin_is_locked()) with assert_spin_lock</a> by Guenter
Roeck</li>
<li><a href="https://android.googlesource.com/kernel/common/+/900e9fd0d5d15c596cacfb89ce007c933cea6e1c">900e9fd
seccomp: fix syscall numbers for x86 and x86_64</a> by Lee Campbell</li>
<li><a href="https://android.googlesource.com/kernel/common/+/a9ba4285aa5722a3b4d84888e78ba8adc0046b28">a9ba428
ARM: add seccomp syscall</a> by Kees Cook</li>
<li><a href="https://android.googlesource.com/kernel/common/+/41900903483eb96602dd72e719a798c208118aad">4190090
ARM: 8087/1: ptrace: reload syscall number after secure_computing() check</a> by
Will Deacon</li>
<li><a href="https://android.googlesource.com/kernel/common/+/abbfed9ed1a78701ef3db74f5287958feb897035">abbfed9
arm64: ptrace: add PTRACE_SET_SYSCALL</a> by AKASHI Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/feb28436457d33fef9f264635291432df4b74122">feb2843
arm64: ptrace: allow tracer to skip a system call</a> by AKASHI Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/dab10731da65a0deba46402ca9fadf6974676cc8">dab1073
asm-generic: add generic seccomp.h for secure computing mode 1</a> by AKASHI
Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/4f12b53f28a751406a27ef7501a22f9e32a9c30b">4f1
2b53  add seccomp syscall for compat task</a> by AKASHI Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/77227239d20ac6381fb1aee7b7cc902f0d14cd85">7722723
arm64: add SIGSYS siginfo for compat task</a> by AKASHI Takahiro</li>
<li><a href="https://android.googlesource.com/kernel/common/+/210957c2bb3b4d111963bb296e2c42beb8721929">210957c
arm64: add seccomp support</a> by AKASHI Takahiro</li>
</ul>