fips140.go

     1  // Copyright 2024 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package fips implements support for the GOFIPS140 build setting.
     6  //
     7  // The GOFIPS140 build setting controls two aspects of the build:
     8  //
     9  //   - Whether binaries are built to default to running in FIPS-140 mode,
    10  //     meaning whether they default to GODEBUG=fips140=on or =off.
    11  //
    12  //   - Which copy of the crypto/internal/fips140 source code to use.
    13  //     The default is obviously GOROOT/src/crypto/internal/fips140,
    14  //     but earlier snapshots that have differing levels of external
    15  //     validation and certification are stored in GOROOT/lib/fips140
    16  //     and can be substituted into the build instead.
    17  //
    18  // This package provides the logic needed by the rest of the go command
    19  // to make those decisions and implement the resulting policy.
    20  //
    21  // [Init] must be called to initialize the FIPS logic. It may fail and
    22  // call base.Fatalf.
    23  //
    24  // When GOFIPS140=off, [Enabled] returns false, and the build is
    25  // unchanged from its usual behaviors.
    26  //
    27  // When GOFIPS140 is anything else, [Enabled] returns true, and the build
    28  // sets the default GODEBUG to include fips140=on. This will make
    29  // binaries change their behavior at runtime to confirm to various
    30  // FIPS-140 details. [cmd/go/internal/load.defaultGODEBUG] calls
    31  // [fips.Enabled] when preparing the default settings.
    32  //
    33  // For all builds, FIPS code and data is laid out in contiguous regions
    34  // that are conceptually concatenated into a "fips object file" that the
    35  // linker hashes and then binaries can re-hash at startup to detect
    36  // corruption of those symbols. When [Enabled] is true, the link step
    37  // passes -fipso={a.Objdir}/fips.o to the linker to save a copy of the
    38  // fips.o file. Since the first build target always uses a.Objdir set to
    39  // $WORK/b001, a build like
    40  //
    41  //	GOFIPS140=latest go build -work my/binary
    42  //
    43  // will leave fips.o behind in $WORK/b001. Auditors like to be able to
    44  // see that file. Accordingly, when [Enabled] returns true,
    45  // [cmd/go/internal/work.Builder.useCache] arranges never to cache linker
    46  // output, so that the link step always runs, and fips.o is always left
    47  // behind in the link step. If this proves too slow, we could always
    48  // cache fips.o as an extra link output and then restore it when -work is
    49  // set, but we went a very long time never caching link steps at all, so
    50  // not caching them in FIPS mode seems perfectly fine.
    51  //
    52  // When GOFIPS140 is set to something besides off and latest, [Snapshot]
    53  // returns true, indicating that the build should replace the latest copy
    54  // of crypto/internal/fips140 with an earlier snapshot. The reason to do
    55  // this is to use a copy that has been through additional lab validation
    56  // (an "in-process" module) or NIST certification (a "certified" module).
    57  // The snapshots are stored in GOROOT/lib/fips140 in module zip form.
    58  // When a snapshot is being used, Init unpacks it into the module cache
    59  // and then uses that directory as the source location.
    60  //
    61  // A FIPS snapshot like v1.2.3 is integrated into the build in two different ways.
    62  //
    63  // First, the snapshot's fips140 directory replaces crypto/internal/fips140
    64  // using fsys.Bind. The effect is to appear to have deleted crypto/internal/fips140
    65  // and everything below it, replacing it with the single subdirectory
    66  // crypto/internal/fips140/v1.2.3, which now has the FIPS packages.
    67  // This virtual file system replacement makes patterns like std and crypto...
    68  // automatically see the snapshot packages instead of the original packages
    69  // as they walk GOROOT/src/crypto/internal/fips140.
    70  //
    71  // Second, ResolveImport is called to resolve an import like crypto/internal/fips140/sha256.
    72  // When snapshot v1.2.3 is being used, ResolveImport translates that path to
    73  // crypto/internal/fips140/v1.2.3/sha256 and returns the actual source directory
    74  // in the unpacked snapshot. Using the actual directory instead of the
    75  // virtual directory GOROOT/src/crypto/internal/fips140/v1.2.3 makes sure
    76  // that other tools using go list -json output can find the sources,
    77  // as well as making sure builds have a real directory in which to run the
    78  // assembler, compiler, and so on. The translation of the import path happens
    79  // in the same code that handles mapping golang.org/x/mod to
    80  // cmd/vendor/golang.org/x/mod when building commands.
    81  //
    82  // It is not strictly required to include v1.2.3 in the import path when using
    83  // a snapshot - we could make things work without doing that - but including
    84  // the v1.2.3 gives a different version of the code a different name, which is
    85  // always a good general rule. In particular, it will mean that govulncheck need
    86  // not have any special cases for crypto/internal/fips140 at all. The reports simply
    87  // need to list the relevant symbols in a given Go version. (For example, if a bug
    88  // is only in the in-tree copy but not the snapshots, it doesn't list the snapshot
    89  // symbols; if it's in any snapshots, it has to list the specific snapshot symbols
    90  // in addition to the “normal” symbol.)
    91  package fips140
    92  
    93  import (
    94  	"cmd/go/internal/base"
    95  	"cmd/go/internal/cfg"
    96  	"cmd/go/internal/fsys"
    97  	"cmd/go/internal/modfetch"
    98  	"cmd/go/internal/str"
    99  	"context"
   100  	"os"
   101  	"path"
   102  	"path/filepath"
   103  	"strings"
   104  
   105  	"golang.org/x/mod/module"
   106  	"golang.org/x/mod/semver"
   107  )
   108  
   109  // Init initializes the FIPS settings.
   110  // It must be called before using any other functions in this package.
   111  // If initialization fails, Init calls base.Fatalf.
   112  func Init() {
   113  	if initDone {
   114  		return
   115  	}
   116  	initDone = true
   117  	initVersion()
   118  	initDir()
   119  	if Snapshot() {
   120  		fsys.Bind(Dir(), filepath.Join(cfg.GOROOT, "src/crypto/internal/fips140"))
   121  	}
   122  }
   123  
   124  var initDone bool
   125  
   126  // checkInit panics if Init has not been called.
   127  func checkInit() {
   128  	if !initDone {
   129  		panic("fips: not initialized")
   130  	}
   131  }
   132  
   133  // Version reports the GOFIPS140 version in use,
   134  // which is either "off", "latest", or a version like "v1.2.3".
   135  // If GOFIPS140 is set to an alias like "inprocess" or "certified",
   136  // Version returns the underlying version.
   137  func Version() string {
   138  	checkInit()
   139  	return version
   140  }
   141  
   142  // Enabled reports whether FIPS mode is enabled at all.
   143  // That is, it reports whether GOFIPS140 is set to something besides "off".
   144  func Enabled() bool {
   145  	checkInit()
   146  	return version != "off"
   147  }
   148  
   149  // Snapshot reports whether FIPS mode is using a source snapshot
   150  // rather than $GOROOT/src/crypto/internal/fips140.
   151  // That is, it reports whether GOFIPS140 is set to something besides "latest" or "off".
   152  func Snapshot() bool {
   153  	checkInit()
   154  	return version != "latest" && version != "off"
   155  }
   156  
   157  var version string
   158  
   159  func initVersion() {
   160  	// For off and latest, use the local source tree.
   161  	v := cfg.GOFIPS140
   162  	if v == "off" || v == "" {
   163  		version = "off"
   164  		return
   165  	}
   166  	if v == "latest" {
   167  		version = "latest"
   168  		return
   169  	}
   170  
   171  	// Otherwise version must exist in lib/fips140, either as
   172  	// a .zip (a source snapshot like v1.2.0.zip)
   173  	// or a .txt (a redirect like inprocess.txt, containing a version number).
   174  	if strings.Contains(v, "/") || strings.Contains(v, `\`) || strings.Contains(v, "..") {
   175  		base.Fatalf("go: malformed GOFIPS140 version %q", cfg.GOFIPS140)
   176  	}
   177  	if cfg.GOROOT == "" {
   178  		base.Fatalf("go: missing GOROOT for GOFIPS140")
   179  	}
   180  
   181  	file := filepath.Join(cfg.GOROOT, "lib", "fips140", v)
   182  	if data, err := os.ReadFile(file + ".txt"); err == nil {
   183  		v = strings.TrimSpace(string(data))
   184  		file = filepath.Join(cfg.GOROOT, "lib", "fips140", v)
   185  		if _, err := os.Stat(file + ".zip"); err != nil {
   186  			base.Fatalf("go: unknown GOFIPS140 version %q (from %q)", v, cfg.GOFIPS140)
   187  		}
   188  	}
   189  
   190  	if _, err := os.Stat(file + ".zip"); err == nil {
   191  		// Found version. Add a build tag.
   192  		cfg.BuildContext.BuildTags = append(cfg.BuildContext.BuildTags, "fips140"+semver.MajorMinor(v))
   193  		version = v
   194  		return
   195  	}
   196  
   197  	base.Fatalf("go: unknown GOFIPS140 version %q", v)
   198  }
   199  
   200  // Dir reports the directory containing the crypto/internal/fips140 source code.
   201  // If Snapshot() is false, Dir returns GOROOT/src/crypto/internal/fips140.
   202  // Otherwise Dir ensures that the snapshot has been unpacked into the
   203  // module cache and then returns the directory in the module cache
   204  // corresponding to the crypto/internal/fips140 directory.
   205  func Dir() string {
   206  	checkInit()
   207  	return dir
   208  }
   209  
   210  var dir string
   211  
   212  func initDir() {
   213  	v := version
   214  	if v == "latest" || v == "off" {
   215  		dir = filepath.Join(cfg.GOROOT, "src/crypto/internal/fips140")
   216  		return
   217  	}
   218  
   219  	mod := module.Version{Path: "golang.org/fips140", Version: v}
   220  	file := filepath.Join(cfg.GOROOT, "lib/fips140", v+".zip")
   221  	zdir, err := modfetch.Unzip(context.Background(), mod, file)
   222  	if err != nil {
   223  		base.Fatalf("go: unpacking GOFIPS140=%v: %v", v, err)
   224  	}
   225  	dir = filepath.Join(zdir, "fips140")
   226  	return
   227  }
   228  
   229  // ResolveImport resolves the import path imp.
   230  // If it is of the form crypto/internal/fips140/foo
   231  // (not crypto/internal/fips140/v1.2.3/foo)
   232  // and we are using a snapshot, then LookupImport
   233  // rewrites the path to crypto/internal/fips140/v1.2.3/foo
   234  // and returns that path and its location in the unpacked
   235  // FIPS snapshot.
   236  func ResolveImport(imp string) (newPath, dir string, ok bool) {
   237  	checkInit()
   238  	const fips = "crypto/internal/fips140"
   239  	if !Snapshot() || !str.HasPathPrefix(imp, fips) {
   240  		return "", "", false
   241  	}
   242  	fipsv := path.Join(fips, version)
   243  	var sub string
   244  	if str.HasPathPrefix(imp, fipsv) {
   245  		sub = "." + imp[len(fipsv):]
   246  	} else {
   247  		sub = "." + imp[len(fips):]
   248  	}
   249  	newPath = path.Join(fips, version, sub)
   250  	dir = filepath.Join(Dir(), version, sub)
   251  	return newPath, dir, true
   252  }
   253
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