68f07389b2
obfuscatedTypesPackage is used to figure out if a name in a dependency package was obfuscated or not. For example, if that package used reflection on a named type, it wasn't obfuscated, so we must have the same information to not obfuscate the same name downstream. obfuscatedTypesPackage could return nil if the package was indirectly imported, though. This can happen if a direct import has a function that returns an indirect type, or if a direct import exposes a name that's a type alias to an indirect type. We sort of dealt with this in two pieces of code by checking for obfPkg!=nil, but a third one did not have this check and caused a panic in the added test case: --- FAIL: TestScripts/reflect (0.81s) testscript.go:397: > env GOPRIVATE=test/main > garble build [stderr] # test/main panic: runtime error: invalid memory address or nil pointer dereference [recovered] panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x8a5e39] More importantly though, the nil check only avoids panics. It doesn't fix the root cause of the problem: that importcfg does not contain indirectly imported packages. The added test case would still fail, as we would obfuscate a type in the main package, but not in the indirectly imported package where the type is defined. To fix this, resurrect a bit of code from earlier garble versions, which uses "go list -toolexec=garble" to fetch a package's export file. This lets us fill the indirect import gaps in importcfg, working around the problem entirely. This solution is still not particularly great, so we add a TODO about possibly rethinking this in the future. It does add some overhead and complexity, though thankfully indirect imports should be uncommon. This fixes a few panics while building the protobuf module. |
4 years ago | |
|---|---|---|
| .github | 5 years ago | |
| internal | 5 years ago | |
| scripts | 5 years ago | |
| testdata | 4 years ago | |
| .gitattributes | 6 years ago | |
| .gitignore | 5 years ago | |
| AUTHORS | 5 years ago | |
| CHANGELOG.md | 5 years ago | |
| CONTRIBUTING.md | 5 years ago | |
| LICENSE | 5 years ago | |
| README.md | 5 years ago | |
| bench_test.go | 5 years ago | |
| go.mod | 5 years ago | |
| go.sum | 5 years ago | |
| hash.go | 5 years ago | |
| main.go | 4 years ago | |
| main_test.go | 5 years ago | |
| position.go | 4 years ago | |
| reverse.go | 4 years ago | |
| runtime_strip.go | 5 years ago | |
| shared.go | 5 years ago | |
README.md
garble
GO111MODULE=on go get mvdan.cc/garble
Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.16 or later.
garble build [build flags] [packages]
The tool also supports garble test to run tests with obfuscated code,
and garble reverse to de-obfuscate text such as stack traces.
See garble -h for up to date usage information.
Purpose
Produce a binary that works as well as a regular build, but that has as little information about the original source code as possible.
The tool is designed to be:
- Coupled with
cmd/go, to support modules and build caching - Deterministic and reproducible, given the same initial source code
- Reversible given the original source, to de-obfuscate panic stack traces
Mechanism
The tool wraps calls to the Go compiler and linker to transform the Go build, in order to:
- Replace as many useful identifiers as possible with short base64 hashes
- Replace package paths with short base64 hashes
- Remove all build and module information
- Strip filenames and shuffle position information
- Strip debugging information and symbol tables via
-ldflags="-w -s" - Obfuscate literals, if the
-literalsflag is given - Remove extra information, if the
-tinyflag is given
By default, the tool obfuscates the packages under the current module. If not
running in module mode, then only the main package is obfuscated. To specify
what packages to obfuscate, set GOPRIVATE, documented at go help private.
Note that commands like garble build will use the go version found in your
$PATH. To use different versions of Go, you can
install them
and set up $PATH with them. For example, for Go 1.16.1:
$ go get golang.org/dl/go1.16.1
$ go1.16.1 download
$ PATH=$(go1.16.1 env GOROOT)/bin:${PATH} garble build
Literal obfuscation
Using the -literals flag causes literal expressions such as strings to be
replaced with more complex variants, resolving to the same value at run-time.
This feature is opt-in, as it can cause slow-downs depending on the input code.
Literal expressions used as constants cannot be obfuscated, since they are
resolved at compile time. This includes any expressions part of a const
declaration.
Tiny mode
When the -tiny flag is passed, extra information is stripped from the resulting
Go binary. This includes line numbers, filenames, and code in the runtime that
prints panics, fatal errors, and trace/debug info. All in all this can make binaries
2-5% smaller in our testing, as well as prevent extracting some more information.
With this flag, no panics or fatal runtime errors will ever be printed, but they
can still be handled internally with recover as normal. In addition, the
GODEBUG environmental variable will be ignored.
Note that this flag can make debugging crashes harder, as a panic will simply
exit the entire program without printing a stack trace, and all source code
positions are set to line 1. Similarly, garble reverse is generally not useful
in this mode.
Speed
garble build should take about twice as long as go build, as it needs to
complete two builds. The original build, to be able to load and type-check the
input code, and finally the obfuscated build.
Go's build cache is fully supported; if a first garble build run is slow, a
second run should be significantly faster. This should offset the cost of the
double builds, as incremental builds in Go are fast.
Determinism and seeds
Just like Go, garble builds are deterministic and reproducible if the inputs
remain the same: the version of Go, the version of Garble, and the input code.
This has significant benefits, such as caching builds or being able to use
garble reverse to de-obfuscate stack traces.
However, it also means that an input package will be obfuscated in exactly the
same way if none of those inputs change. If you want two builds of your program
to be entirely different, you can use -seed to provide a new seed for the
entire build, which will cause a full rebuild.
If any open source packages are being obfuscated, providing a custom seed can also provide extra protection. It could be possible to guess the versions of Go and garble given how a public package was obfuscated without a seed.
Caveats
Most of these can improve with time and effort. The purpose of this section is to document the current shortcomings of this tool.
-
Exported methods are never obfuscated at the moment, since they could be required by interfaces and reflection. This area is a work in progress.
-
It can be hard for garble to know what types will be used with reflection, including JSON encoding or decoding. If your program breaks because a type's names are obfuscated when they should not be, you can add an explicit hint:
type Message struct { Command string Args string } // Never obfuscate the Message type. var _ = reflect.TypeOf(Message{}) -
Go plugins are not currently supported; see #87.
Contributing
We welcome new contributors. If you would like to contribute, see CONTRIBUTING.md as a starting point.