diff --git a/sw/CMakeLists.txt b/sw/CMakeLists.txt
index 37454a09a..5d037431c 100644
--- a/sw/CMakeLists.txt
+++ b/sw/CMakeLists.txt
@@ -19,6 +19,7 @@ include(ExternalProject)
 
 add_subdirectory(device)
 
+include(cmake/busybox.cmake)
 include(cmake/linux.cmake)
 include(cmake/opensbi.cmake)
 include(cmake/uboot.cmake)
diff --git a/sw/cmake/busybox.cmake b/sw/cmake/busybox.cmake
new file mode 100644
index 000000000..dfa542e33
--- /dev/null
+++ b/sw/cmake/busybox.cmake
@@ -0,0 +1,89 @@
+# Copyright lowRISC contributors.
+# Licensed under the Apache License, Version 2.0, see LICENSE for details.
+# SPDX-License-Identifier: Apache-2.0
+
+function(mocha_busybox OUTPUT_NAME)
+  set(BUSYBOX_BUILD_NAME ${OUTPUT_NAME}_build)
+  # Busybox repository and tag to use.
+  #TODO change this URL to https://github.com/lowrisc/busybox
+  # once the mocha-devel branch is pushed there.
+  set(BUSYBOX_REPOSITORY https://github.com/ziuziakowska/busybox)
+  set(BUSYBOX_TAG mocha-devel)
+
+  # configure command - load Mocha defconfig file.
+  set(CONFIGURE_COMMAND
+      make
+      mocha_defconfig
+  )
+
+  # Clang flags.
+  set(FLAGS
+      " \
+      -target riscv64-linux-musl \
+      -march=rv64imaczcherihybrid_zcherilevels \
+      -mabi=l64pc128 \
+      -mno-relax \
+      -static \
+      -isystem $ENV{LIBC_PURECAP_INCLUDE} \
+      -isystem $ENV{SYSROOT_PURECAP} \
+      -L $ENV{LIBC_PURECAP_LIB} \
+      -B $ENV{LIBC_PURECAP_LIB} \
+      -L $ENV{COMPILER_RT_PURECAP} \
+      -B $ENV{COMPILER_RT_PURECAP} \
+      -Xclang -target-feature -Xclang +cheri-bounded-vararg \
+      -Xclang -target-feature -Xclang +cheri-bounded-memarg-caller \
+      -Xclang -target-feature -Xclang +cheri-bounded-memarg-callee \
+      "
+  )
+
+  # build command.
+  set(BUILD_COMMAND
+      make
+      ARCH=riscv
+      "CC=clang ${FLAGS}"
+      HOSTCC=gcc
+      "LD=ld.lld"
+      "CFLAGS_busybox=--unwindlib=none ${FLAGS} -fuse-ld=lld"
+  )
+
+  # Busybox built images.
+  set(BUSYBOX_ARTEFACTS
+      busybox
+  )
+
+  # install command - copy busybox images to the root of the external project directory.
+  set(INSTALL_COMMAND
+      cp ${BUSYBOX_ARTEFACTS} <INSTALL_DIR>
+  )
+
+  ExternalProject_Add(
+      ${BUSYBOX_BUILD_NAME}
+      PREFIX ${BUSYBOX_BUILD_NAME}
+      GIT_REPOSITORY ${BUSYBOX_REPOSITORY}
+      GIT_TAG ${BUSYBOX_TAG}
+      GIT_SHALLOW true
+      # Linux builds in it's own source tree.
+      BUILD_IN_SOURCE true
+      # make is job server aware.
+      BUILD_JOB_SERVER_AWARE true
+      CONFIGURE_COMMAND ${CONFIGURE_COMMAND}
+      BUILD_COMMAND ${BUILD_COMMAND}
+      INSTALL_COMMAND ${INSTALL_COMMAND}
+      # suppress output from stdout.
+      LOG_DOWNLOAD true
+      LOG_UPDATE true
+      LOG_PATCH true
+      LOG_CONFIGURE true
+      LOG_BUILD true
+      LOG_INSTALL true
+      LOG_MERGED_STDOUTERR true
+      LOG_OUTPUT_ON_FAILURE true
+  )
+
+  add_executable(${OUTPUT_NAME} IMPORTED GLOBAL)
+  set_target_properties(${OUTPUT_NAME} PROPERTIES
+      IMPORTED_LOCATION ${CMAKE_CURRENT_BINARY_DIR}/${BUSYBOX_BUILD_NAME}/src/${BUSYBOX_BUILD_NAME}/busybox
+  )
+endfunction()
+
+mocha_busybox(busybox)