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OS integration guide

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Daniel Micay 2019-07-18 07:21:27 -04:00
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README.md
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@ -79,6 +79,59 @@ this allocator offers across different size classes. The intention is that this
will be offered as part of hardened variants of the Bionic and musl C standard
libraries.
# OS integration
## Android-based operating systems
On GrapheneOS, hardened\_malloc is integrated into the standard C library as
the standard malloc implementation. Other Android-based operating systems can
reuse the integration code to provide it. If desired, jemalloc can be left as
a runtime configuration option by only conditionally using hardened\_malloc to
give users the choice between performance and security. However, this reduces
security for threat models where persistent state is untrusted, i.e. verified
boot and attestation (see the [attestation sister
project](https://attestation.app/about)).
Make sure to raise `vm.max_map_count` substantially too to accomodate the very
large number of guard pages created by hardened\_malloc. This can be done in
`init.rc` (`system/core/rootdir/init.rc`) near the other virtual memory
configuration:
write /proc/sys/vm/max_map_count 524240
This is unnecessary if you set `CONFIG_GUARD_SLABS_INTERVAL` to a very large
value in the build configuration.
## Traditional Linux-based operating systems
On traditional Linux-based operating systems, hardened\_malloc can either be
integrated into the libc implementation as a replacement for the standard
malloc implementation or loaded as a dynamic library. Rather rebuilding each
executable to be linked against it, it can be added as a preloaded library to
`/etc/ld.so.preload`. For example, with `libhardened_malloc.so` installed to
`/usr/local/lib/libhardened_malloc.so`, add that full path as a line to the
`/etc/ld.so.preload` configuration file:
/usr/local/lib/libhardened_malloc.so
The format of this configuration file is a whitespace-separated list, so it's
good practice to put each library on a separate line.
Using the `LD_PRELOAD` environment variable to load it on a case-by-case basis
will not work when `AT_SECURE` is set such as with setuid binaries. It's also
generally not a recommended approach for production usage. The recommendation
is to enable it globally and make exceptions for performance critical cases by
running the application in a container / namespace without it enabled.
Make sure to raise `vm.max_map_count` substantially too to accomodate the very
large number of guard pages created by hardened\_malloc. As an example, in
`/etc/sysctl.d/hardened_malloc.conf`:
vm.max_map_count = 524240
This is unnecessary if you set `CONFIG_GUARD_SLABS_INTERVAL` to a very large
value in the build configuration.
## Configuration
You can set some configuration options at compile-time via arguments to the