nixos/malloc: configure system-wide malloc provider

Currently, this uses the somewhat crude method of setting LD_PRELOAD in the
system environment.  This works, but should be considered a stepping stone to
a more robust solution.

nixos/modules/config/malloc.nix

@@ -0,0 +1,91 @@
+{ config, lib, pkgs, ... }:
+with lib;
+
+let
+  cfg = config.environment.memoryAllocator;
+
+  # The set of alternative malloc(3) providers.
+  providers = {
+    "graphene-hardened" = rec {
+      libPath = "${pkgs.graphene-hardened-malloc}/lib/libhardened_malloc.so";
+      description = ''
+        An allocator designed to mitigate memory corruption attacks, such as
+        those caused by use-after-free bugs.
+      '';
+    };
+
+    "jemalloc" = {
+      libPath = "${pkgs.jemalloc}/lib/libjemalloc.so";
+      description = ''
+        A general purpose allocator that emphasizes fragmentation avoidance
+        and scalable concurrency support.
+      '';
+    };
+  };
+
+  providerConf = providers."${cfg.provider}";
+
+  # An output that contains only the shared library, to avoid
+  # needlessly bloating the system closure
+  mallocLib = pkgs.runCommand "malloc-provider-${cfg.provider}"
+    rec {
+      preferLocalBuild = true;
+      allowSubstitutes = false;
+      origLibPath = providerConf.libPath;
+      libName = baseNameOf origLibPath;
+    }
+    ''
+      mkdir -p $out/lib
+      cp -L $origLibPath $out/lib/$libName
+    '';
+
+  # The full path to the selected provider shlib.
+  providerLibPath = "${mallocLib}/lib/${mallocLib.libName}";
+in
+
+{
+  meta = {
+    maintainers = [ maintainers.joachifm ];
+  };
+
+  options = {
+    environment.memoryAllocator.provider = mkOption {
+      type = types.enum ([ "libc" ] ++ attrNames providers);
+      default = "libc";
+      description = ''
+        The system-wide memory allocator.
+        </para>
+
+        <para>
+        Briefly, the system-wide memory allocator providers are:
+        <itemizedlist>
+        <listitem><para><literal>libc</literal>: the standard allocator provided by libc</para></listitem>
+        ${toString (mapAttrsToList
+            (name: value: "<listitem><para><literal>${name}</literal>: ${value.description}</para></listitem>")
+            providers)}
+        </itemizedlist>
+        </para>
+
+        <warning>
+        <para>
+        Selecting an alternative allocator (i.e., anything other than
+        <literal>libc</literal>) may result in instability, data loss,
+        and/or service failure.
+        </para>
+        </warning>
+
+        <note>
+        <para>
+        Changing this option does not affect the current session.
+        </para>
+        </note>
+
+        <para>
+      '';
+    };
+  };
+
+  config = mkIf (cfg.provider != "libc") {
+    environment.variables.LD_PRELOAD = providerLibPath;
+  };
+}

nixos/modules/module-list.nix

@@ -19,6 +19,7 @@
   ./config/iproute2.nix
   ./config/krb5/default.nix
   ./config/ldap.nix
+  ./config/malloc.nix
   ./config/networking.nix
   ./config/no-x-libs.nix
   ./config/nsswitch.nix