The OCCAM saga
Project description
Description
OCCAM is a whole-program partial evaluator for LLVM bitcode that aims at debloating programs and shared/static libraries running in a specific deployment context.
OCCAM architecture
Docker
A pre-built and installed version of OCCAM can be obtained using Docker:
docker pull sricsl/occam:bionic
docker run -v `pwd`:/host -it sricsl/occam:bionic
Alternatively, it can be built and installed from source as follows.
Prerequisites
OCCAM currently works on Linux, macOS, and FreeBSD. It depends on an installation of LLVM. OCCAM currently is built on the top of llvm-10.0 which requires a C++ compiler supporting c++14. You will also need the Google protocol buffer compiler protoc
and the corresponding Python package. Some OCCAM components (such as sea-dsa and crab require the boost library >= 1.65.
If you need to generate application bitcode (that OCCAM operates on), you will want to install WLLVM, either from the the pip package or the GitHub repository.
The test harness also requires lit and FileCheck
. FileCheck
can often be found in the binary directory of your LLVM installation. However, if you built your own, you may need to read this. Hint: the build produces it, but does not install it. (Try locate FileCheck
, then copy it to the bin
directory.)
Detailed configuration instructions for Ubuntu 18.04 can be gleaned from bootstrap.sh as well as the Travis CI scripts for each branch .travis.yml.
Building and Installing
Set where OCCAM's library will be stored:
export OCCAM_HOME={path to location in your home directory}
Point to your LLVM's location, if non-standard:
export LLVM_HOME=/usr/local/llvm-10.0
export LLVM_CONFIG=llvm-config-10.0
Set where system libraries, including Google Protocol Buffers, are located:
export LD_FLAGS='-L/usr/local/lib'
Clone, build, and install OCCAM with:
git clone --recurse-submodules https://github.com/SRI-CSL/OCCAM.git
make
make install
make test
Using OCCAM
You can choose to record logs from OCCAM by setting the following variables:
export OCCAM_LOGFILE={absolute path to log location}
export OCCAM_LOGLEVEL={INFO, WARNING, or ERROR}
Using razor
razor
is a pip package that relies on the same dynamic library as occam
. So you should first build and install occam
as described above. razor
provides the commandline tool slash
for end users. You can either install razor
from this repository, or you can use:
pip install razor
To install an editable version from this repository:
make -f Makefile develop
This may require sudo privileges. Either way you can now use slash
:
slash [--work-dir=<dir>] [--force] [--no-strip] [--intra-spec-policy=<type>] [--inter-spec-policy=<type>] [--use-pointer-analysis] [--enable-config-prime] <manifest>
where
type=none|aggressive|nonrec-aggressive|bounded|onlyonce
The value none
will prevent any inter or intra-module specialization. The value aggressive
specializes a call if any parameter is a constant. The value nonrec-aggressive
specializes a call if the function is non-recursive and any parameter is a constant. The value bounded
makes at most k
copies where k
can be chosen by option --max-bounded-spec
. The value onlyonce
makes a copy of a function only if the function is called exactly once.
To function correctly slash
calls LLVM tools such as opt
and clang++
. These should be available in your PATH
, and be the currently supported version (10.0). Like wllvm
, slash
, will pay attention to the environment variables LLVM_OPT_NAME
and LLVM_CXX_NAME
if your version of these tools is adorned with suffixes.
The Manifest
The manifest for slash
should be valid JSON. The following keys have meaning:
-
main
: a path to the bitcode module containing themain
entry point. -
modules
: a list of paths to the other bitcode modules needed. -
binary
: the name of the desired executable. -
native_libs
: a list of flags (-lm
,-lc
,-lpthread
) or paths to native objects (.o
,.a
,.so
,.dylib
) -
ldflags
: a list of linker flags such as--static
,--nostdlib
-
name
: the program name -
static_args
: the list of static arguments you wish to specialize in the main() ofmain
. -
dynamic_args
: a number that indicates the arguments the specialized program will receive at runtime. If this key is omitted then the default value is 0 which means that the specialized program does not expect any parameter. -
lib_spec
: list of library bitcode you wish to specialize with respect tomain
or a list ofmain
functions given bymain_spec
. -
main_spec
: list of bitcode modules each containing amain
function used bylib_spec
.
As an example, (see examples/linux/apache
), to previrtualize apache:
{ "main" : "httpd.bc"
, "binary" : "httpd_slashed"
, "modules" : ["libapr-1.so.bc", "libaprutil-1.so.bc", "libpcre.so.bc"]
, "native_libs" : ["-lcrypt", "-ldl", "-lpthread"]
, "name" : "httpd"
, "static_args" : ["-d", "/var/www"]
}
Another example, (see examples/linux/musl_nweb
), specializes nweb
with musl libc.c
:
{ "main" : "nweb.o.bc"
, "binary" : "nweb_razor"
, "modules" : ["libc.a.bc"]
, "native_libs" : ["crt1.o", "libc.a"]
, "ldflags" : ["-static", "-nostdlib"]
, "name" : "nweb"
, "static_args" : ["8181", "./root"]
, "dynamic_args" : "0"
}
A third example, (see examples/linux/tree
), illustrates the use of the dynamic_args
field to partially specialize the arguments to the tree
utility.
{ "main" : "tree.bc"
, "binary" : "tree"
, "modules" : []
, "native_libs" : []
, "ldflags" : [ "-O2" ]
, "name" : "tree"
, "static_args" : ["-J", "-h"]
, "dynamic_args" : "1"
}
The specialized program will output its results in JSON notation (-J) that will include a human readable size field (-h). The specialized program expects one extra argument, either a directory or another flag to output the contents of the current working directory.
This material is based upon work supported by the National Science Foundation under Grant ACI-1440800. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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