Add GrapheneOS hardened_malloc documentation.

security/hardened_malloc.adoc

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+= GrapheneOS hardened_malloc
+
+Version: 0.0.0.0
+
+
+This documentation contains the complete set of commands to use
+https://github.com/GrapheneOS/hardened_malloc[GrapheneOS' hardened_malloc] memory allocator as the
+system's default memory allocator. These instructions apply to both musl and glibc C libraries on
+Unix-based and Unix-like systems.
+
+
+== Increase Permitted Amount of Memory Pages
+
+Add `vm.max_map_count = 1048576` to `/etc/sysctl.conf` to accomodate hardened_malloc's large amount
+of guard pages
+
+== Clone hardened_malloc Source Code
+
+`git clone https://github.com/GrapheneOS/hardened_malloc.git`
+
+== Enter hardened_malloc Local Git Repository
+
+`cd hardened_malloc/`
+
+== Compile hardened_malloc
+
+`make <arguments>`
+
+`CONFIG_N_ARENA=n` can be adjusted to increase parallel performance at the expense of memory usage,
+or decrease memory usage at the expense of parallel performance, where `n` is an integer. For
+low-memory systems, `VARIANT=light` can be used to compile the light variant of hardened_malloc,
+which sacrifices some security for much less memory usage.
+
+== Copy Compiled hardened_malloc Library
+
+`cp out/libhardened_malloc.so <target_path>`
+
+== Set System to Preload hardened_malloc on Boot
+
+musl-based systems: Add `export LD_PRELOAD=<hardened_malloc_path>` to `/etc/environment` +
+glibc-based systems: Add `<hardened_malloc_path>` to `/etc/ld.so.preload`