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hex0punk / wally

Function callpath mapping analysis tool for Go
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Wally
wally the cartographer

Wally is a static analysis tool for mapping function paths in code. It can be used for:

UI Demo

https://github.com/hex0punk/wally/assets/1915998/1965f765-5437-4486-8c62-c125455b1f01

Read about this graph and how to explore it in the Exploring the graph with wally server section

The basics

Why is it called Wally?

Because Wally is a cartographer, I like Monkey Island, and I wanted it to be called that :).

Why not just grep instead?

So you are analyzing a Go-based application and you need to find all HTTP and RPC routes. You can run grep or ripgrep to find specific patterns that'd point you to routes in the code but:

  1. You'd need to parse through a lot of unnecessary strings.
  2. You may end up with functions that are similar to those you are targeting but have nothing to do with HTTP or RPC.
  3. Grep won't solve constant values that indicate methods and route paths.

What can Wally do that grep can't?

Wally currently supports the following features:

Use cases - example

Mapping routes for security analysis

You are conducting an analysis of a monorepo containing multiple microservices. Often, these sorts of projects rely heavily on gRPC, which generates code for setting up gRPC routes via functions that call Invoke. Other services can then use these functions to call each other.

One of the built-in indicators in wally will allow it to find functions that call Invoke for gRPC routes, so you can get a nice list of all gRPC method calls for all your microservices. Further, with --ssa you can also map the chains of methods gRPC calls necessary to reach any given gRPC route. With wally, you can then answer:

Planning fuzzing efforts by examining call path tolerance

Say you are evaluating some microservices code in a monorepo and found several functions that seemed like good fuzzing targets due to their complexity and the type of data they handle. However, before fuzzing just for fuzzing’s sake, you want to answer the following:

To learn how to answer the above questions, jump to the section on using wally to detect fault tolerance of call paths

Wally configurations

Wally needs a bit of hand-holding. Though it can also do a pretty good job at guessing paths, it helps a lot if you tell it the packages and functions to look for, along with the parameters that you are hoping to discover and map. So, to help Wally do the job, you can specify a configuration file in YAML that defines a set of indicators.

[!TIP] If you are just interested in use cases of a single function, you can run Wally on single function search mode

Wally runs a number of indicators which are basically clues as to whether a function in code may be related to a gRPC or HTTP route. By default, wally has a number of built-in indicators which check for common ways to set up and call HTTP and RPC methods using standard and popular libraries. However, sometimes a codebase may have custom methods for setting up HTTP routes or for calling HTTP and RPC services. For instance, when reviewing Nomad, you can give Wally the following configuration file with Nomad-specific indicators:

indicators:
  - id: nomad-1
    package: "github.com/hashicorp/nomad/command/agent"
    type: ""
    function: "forward"
    indicatorType: 1
    receiverType: "ACL"    # optional 
    params:
      - name: "method"
  - id: nomad-2
    package: "github.com/hashicorp/nomad/nomad"
    type: ""
    function: "RPC"
    indicatorType: 1
    params:               # optional
      - name: "method"    # optional 
  - id: nomad-3
    package: "github.com/hashicorp/nomad/api"
    type: "s"
    function: "query"
    indicatorType: 1
    params:
        pos: 0           # optioncal

Note that you can specify the parameter that you want Wally to attempt to solve the value to. If you don't know the name of the parameter (per the function signature), you can give it the position in the signature. You can then use the --config or -c flag along with the path to the configuration file.

Filtering Matches

You can exclude the following from the analysis performed by Wally

Match Filters vs. Path Filters

You can provide a match filter or path filters to wally.

Route Detection

A good test project to run it against is nomad because it has a lot of routes set up and called all over the place. I suggest the following:

  1. Clone this project.
  2. In a separate directory, clone nomad.
  3. Build this project by running go build.
  4. Navigate to the root of the directory where you cloned nomad (path/to/nomad).
  5. Create a configuration file named .wally.yaml with the content shown in the previous section of this README, and save it to the root of the nomad directory.
  6. Run the following command from the nomad root:
$ <path/to/wally/wally> map -p ./... -vvv

Running Wally with Docker

Wally can be easily run using Docker. Follow these steps:

  1. Clone this project.

  2. In a separate directory, clone nomad.

  3. Build the Docker Image:

    docker build -t go-wally .

  4. Run an interactive shell inside the Docker container

    docker run -it go-wally /bin/sh

  5. Run Wally with Docker, specifying the necessary parameters, such as the project path, configuration file, etc.:

    docker run -w /<PROJECT>/ -v $(pwd):/<PROJECT> go-wally map /<PROJECT>/... -vvv

    Adjust the flags (-p, -vvv, etc.) as needed for your use case.

  6. If you have a specific configuration file (e.g., .wally.yaml), you can mount it into the container:

    docker run -w </PROJECT> -v $(pwd):</PROJECT> -v </PATH/TO/.wally.yaml>:</PROJECT>/.wally.yaml go-wally map -c .wally.yaml -p ./... --max-paths 50 -vvv

    This will run Wally within a Docker container, analyzing your Go code for HTTP and RPC routes based on the specified indicators and configurations.

  7. Optionally, if you encountered any issues during the Docker build, you can revisit the interactive shell inside the container for further debugging.

  8. After running Wally, you can check the results and the generated PNG or XDOT graph output, as explained in the README.

Callpath analysis

Wally should work even if you are not able to build the project you want to run it against. However, if you can build the project without any issues, you can run Wally using the --ssa flag, at which point Wally will be able to do the following:

When using the --ssa flag you can expect output like this:

===========MATCH===============
ID:  14554c2a-41ee-4634-831d-6fc49c70c80d
Indicator ID:  1
Package:  github.com/hashicorp/cronexpr
Function:  Parse
Params:
Enclosed by:  (*github.com/hashicorp/nomad/nomad/structs.PeriodicConfig).Validate
Position /Users/hex0punk/Tests/nomad/nomad/structs/structs.go:5638
Possible Paths: 1
    Path 1 (filter limited):
        [Validate] nomad/structs/structs.go:5614:26 --->

===========MATCH===============
ID:  6a876579-6b72-4501-af5b-5028c84a1c77
Indicator ID:  1
Package:  github.com/hashicorp/cronexpr
Function:  Parse
Params:
Enclosed by:  (*github.com/hashicorp/nomad/nomad/structs.PeriodicConfig).Validate
Position /Users/hex0punk/Tests/nomad/nomad/structs/structs.go:5644
Possible Paths: 1
    Path 1 (filter limited):
        [Validate] nomad/structs/structs.go:5614:26 --->

===========MATCH===============
ID:  eeaa94b1-28a8-41b8-a1e3-7a0d665a1e4d
Indicator ID:  1
Package:  github.com/hashicorp/cronexpr
Function:  Parse
Params:
Enclosed by:  github.com/hashicorp/nomad/nomad/structs.CronParseNext
Position /Users/hex0punk/Tests/nomad/nomad/structs/structs.go:5677
Possible Paths: 28
    Path 1 (RECOVERABLE):
        nomad.[Plan] nomad/job_endpoint.go:1949:57 --->
        structs.[Next] nomad/structs/structs.go:5693:24 --->
        [CronParseNext] (recoverable) nomad/structs/structs.go:5670:6 --->
    Path 2 (RECOVERABLE):
        nomad.[Plan] nomad/job_endpoint.go:1949:57 --->
        structs.[Next] nomad/structs/structs.go:5699:27 --->
        [CronParseNext] (recoverable) nomad/structs/structs.go:5670:6 --->
    Path 3 (node limited) (RECOVERABLE):
        nomad.[leaderLoop] nomad/leader.go:247:34 --->
        nomad.[establishLeadership] nomad/leader.go:412:33 --->
        nomad.[SetEnabled] nomad/periodic.go:167:3 --->
        nomad.[run] nomad/periodic.go:332:14 --->
        nomad.[dispatch] nomad/periodic.go:342:38 --->
        structs.[Next] nomad/structs/structs.go:5693:24 --->
        [CronParseNext] (recoverable) nomad/structs/structs.go:5670:6 --->

Filtering call path analysis

When running Wally in SSA mode against large codebases wally might run get lost in external libraries used by the target code. By default, Wally will filter call path functions to those belonging only to the module of each match discovered for a given indicator. This is what you'd want in most case. However, you can also filter analysis to only the packages container a string prefix which you can specify using -f followed by a string. For instance, when using wally to find HTTP and gRPC routes in nomad, you can to type the command below.

$ wally map -p ./... --ssa -vvv -f "github.com/hashicorp/" --max-paths 50

Additionally, there may be cases where a module cannot be found for a given function match e.g., in the case the function belongs to the standard library). By setting a filter using -f <filter> and keeping module-only set to true, wally will first default to filtering by the module strings and use the specified filter string whenever it cannot detect a module for a function match.

Where -f defines a filter for the call stack search function.

Using an empty filter with --module-only=false

You can also allow wally to look beyond packages belonging to the target module by passing an empty filter and setting module-only to false (-f "" --module-only=false). However, keep in mind that doing so might result in wally getting stuck in some loop as it encounters recursive calls or very lengthy paths in scary dependency forests.

[!IMPORTANT] You can also use --max-paths and an integer to limit the number of recursive calls Wally makes when mapping call paths (50 tends to be a good number). This will limit the paths you see in the output, but using a high enough number should still return helpful paths. Experiment with --max-paths, --max-funcs, -f, or all three to get the results you need or expect.

Wally has the following options to limit the search. These options can help refine the results, but can be used for various experimental uses of Wally as well.

Limiter modes

At its core, Wally uses various algorithms available via the golang.org/x/tools/go/callgraph library. These algorithms can generate spurious results at times which results in functions that go past main at the top of callpaths. To wrangle some of these sort of results, we perform a basic set of logical checks to eliminate or limit incorrect call path functions/nodes. By default, Wally uses the very-strict (level 4) limiter mode. Use the other modes if you are not getting the results you expected. You can specify how the limiting is done using the --limiter-mode flag, followed by one of the modes levels below:

Simple mode

Using -s or --simple tells wally to only focus not on call sites but instead the relation between functions. In this mode, wally does the following:

This allows you to get a higher level view of the relation between packages, functions, etc. in your code.

Analyzing individual paths

Rather than using a yaml configuration file, you can use wally map search for mapping paths to individual functions. For instance:

$ wally map search  -p ./... --func Parse --pkg github.com/hashicorp/cronexpr -f github.com/hashicorp/ -vvv

The options above map to the following

Using Wally in Fuzzing Efforts to Determine Fault Tolerance of Call Paths

Wally can now tell you which paths to a target function will recover in case of a panic triggered by that target function. A detailed explanation can be found here.

Using the single function search mode, we can determine which call paths to a given target function would recover in response to a panic

$ wally map search  -p ./... --func PrintOrPanic --pkg github.com/hex0punk/wally/sampleapp/printer -f github.com/hex0punk/wally/sampleapp -vvv

===========MATCH===============
ID:  f9241d61-d19e-4847-b458-4f53a86ed5c5
Indicator ID:  1
Package:  github.com/hex0punk/wally/samppleapp/printer
Function:  PrintOrPanic
Params:
Enclosed by:  github.com/hex0punk/wally/samppleapp.printCharSafe$1
Position /Users/alexuseche/Projects/wally/sampleapp/main.go:17
Possible Paths: 1
    Path 1 (RECOVERABLE):
        main.[main] main.go:11:15 --->
        main.[`printCharSafe`] main.go:16:16 --->
        safe.[RunSafely] (recoverable) safe/safe.go:12:4 --->
        main.[printCharSafe$1] main.go:16:17 --->

===========MATCH===============
ID:  eb72e837-31ba-4945-97b1-9432900ae3f9
Indicator ID:  1
Package:  github.com/hex0punk/wally/samppleapp/printer
Function:  PrintOrPanic
Params:
Enclosed by:  github.com/hex0punk/wally/samppleapp.printChar
Position /Users/alexuseche/Projects/wally/sampleapp/main.go:22
Possible Paths: 1
    Path 1:
        main.[main] main.go:12:11 --->
        main.[printChar] main.go:21:6 --->

Total Results:  2

Paths marked with (RECOVERABLE) will be fault tolerant. The function containing the recover() block is marked in the results as (recoverable)

Visualizing paths with wally

To make visualization of callpaths easier, wally can lunch a server on localhost when via a couple methods:

After an analysis by passing the --server flag to the map command. For instance:

$ wally map -p ./... -c .wally.yaml --ssa -f "github.com/hashicorp/nomad" --server

Or, using the server subcommand and passing a wally json file:

 $ wally server -p ./nomad-wally.json -P 1984

Next, open a browser and head to the address in the output.

Exploring the graph with wally server

Graphs are generated using the cosmograph library. Each node represents a function call in code. The colors are not random. Each color has a a different purpose to help you make good use of the graph.

Finding node. This is a node discovered via wally indicators. Every finding node is the end of a path

This node is the root of a path to a finding node.

Intermediate node between a root and a finding node.

This node servers both as the root node to a path and an intermediary node for one or more paths

Viewing paths

Clicking on any node will highlight all possible paths to that node. Click anywhere other than a node to exist the path selection view.

Viewing findings

Clicking on any finding node will populate the section on the left with information about the finding.

Searching nodes

Start typing on the search bar on the left to find a node by name.

PNG and XDOT Graph output

When using the --ssa flag, you can also use -g or --graph to indicate a path for a PNG or XDOT containing a Graphviz-based graph of the call stacks. For example, running:

$ wally map -p ./... --ssa -vvv -f "github.com/hashicorp/nomad/" -g ./mygraph.png

From nomad/command/agent will output this graph:

Specifying a filename with a .xdot extension will create an xdot file instead.

Advanced options

Using DFS vs BFS

When running Wally without --max-paths or --max-funcs, and with a --limiter-mode of 3 (Strict) or higher, both BFS (Breadth-First Search) and DFS (Depth-First Search) should identify the same nodes and sinks, ensuring that if a path from A to Z passing through D exists, both algorithms will find it. However, the handling of cyclic calls differs between the two approaches:

This is intentional, as it allows the user to use either option to fit their needs.

For example, consider the following path:

- foo:128
- bar:44
- foo:124
- myFunc:12

In this path, foo at line 128 calls bar, which in turn calls foo again at line 124, eventually calling myFunc. In this scenario, BFS will continue to collect nodes even if foo is called multiple times as long as foo is called from different positions (line and column number), while DFS will consider the second call to foo as part of a cycle and will not continue further along that path.

Both methods will avoid cyclical calls if, say, foo is called twice in a path from the same line number. For instance, you will never see a result such as the one below:

- foo:124
- bar:44
- foo:124
- myFunc:12

The power of Wally

At its core, Wally is, essentially, a function mapper. You can define functions in configuration files that have nothing to do with HTTP or RPC routes to obtain the same information that is described here.

Logging

You can add logging statements as needed during development in any function with a Navigator receiver like this: n.Logger.Debug("your message", "a key", "a value").

Troubleshooting

At the moment, wally will often give you duplicate stack paths, where you'd notice a path of, say, A->B->C is repeated a couple of times or more. Based on my testing and debugging this is a drawback of the cha algorithm from Go's callgraph package, which wally uses for the call stack path functionality. I am experimenting with other available algorithms in go/callgraph/ to determine what the best option to minimize such issues (while getting accurate call stacks) could be and will update wally's code accordingly. In the case that we stick to the cha algorithm, I will write code to filter duplicates.

When running in SSA mode, I get findings with no enclosed functions reported

This is often caused by issues in the target code base. Make sure you are able to build the target codebase. You may want to run go build and fix any issues reported by the compiler. Then, run wally again against it.

Wally appears to be stuck in loop

See the section on Filtering call path analysis

Viewing help

Viewing the description of each command

map

$ wally map --help

map search (single function)

$ wally map search --help

server

$ wally map --help

Contributing

Feel free to open issues and send PRs. Please.