Only maintain maps between current and previous selinux versions.

New maintenance scheme for mapping files:
Say, V is the current SELinux platform version, then at any point in time we
only maintain (V->V-1) mapping. (V->V-n) map is constructed from top (V->V-n+1)
and bottom (V-n+1->V-n) without changes to previously maintained mapping files.

Caveats:
- 26.0.cil doesn't technically represent 27.0->26.0 map, but rather
current->26.0. We'll fully migrate to the scheme with future releases.

Bug: 67510052
Test: adding new public type only requires changing the latest compat map
Change-Id: Iab5564e887ef2c8004cb493505dd56c6220c61f8

.gitignore

@@ -0,0 +1,2 @@
+*.pyc
+*.*~

Android.bp

@@ -35,21 +35,36 @@ se_filegroup {
 
 se_cil_compat_map {
     name: "26.0.cil",
-    srcs: [
-        ":26.0.board.compat.map",
-    ],
+    bottom_half: [":26.0.board.compat.map"],
+    top_half: "27.0.cil",
 }
 
 se_cil_compat_map {
     name: "27.0.cil",
-    srcs: [
-        ":27.0.board.compat.map",
-    ],
+    bottom_half: [":27.0.board.compat.map"],
+    top_half: "28.0.cil",
 }
 
 se_cil_compat_map {
     name: "28.0.cil",
-    srcs: [
-        ":28.0.board.compat.map",
-    ],
+    bottom_half: [":28.0.board.compat.map"],
+    // top_half: "29.0.cil",
+}
+
+se_cil_compat_map {
+    name: "26.0.ignore.cil",
+    bottom_half: ["private/compat/26.0/26.0.ignore.cil"],
+    top_half: "27.0.ignore.cil",
+}
+
+se_cil_compat_map {
+    name: "27.0.ignore.cil",
+    bottom_half: ["private/compat/27.0/27.0.ignore.cil"],
+    top_half: "28.0.ignore.cil",
+}
+
+se_cil_compat_map {
+    name: "28.0.ignore.cil",
+    bottom_half: ["private/compat/28.0/28.0.ignore.cil"],
+    // top_half: "29.0.ignore.cil",
 }

build/soong/cil_compat_map.go

@@ -21,10 +21,28 @@ import (
 	"android/soong/android"
 	"fmt"
 	"io"
+
+	"github.com/google/blueprint/proptools"
+	"github.com/google/blueprint"
 )
 
 var (
 	pctx = android.NewPackageContext("android/soong/selinux")
+
+	combine_maps = pctx.HostBinToolVariable("combine_maps", "combine_maps")
+	combineMapsCmd = "${combine_maps} -t ${topHalf} -b ${bottomHalf} -o $out"
+	combineMapsRule = pctx.StaticRule(
+		"combineMapsRule",
+		blueprint.RuleParams{
+			Command: combineMapsCmd,
+			CommandDeps: []string{"${combine_maps}"},
+		},
+		"topHalf",
+		"bottomHalf",
+	)
+
+	String = proptools.String
+	TopHalfDepTag = dependencyTag{name: "top"}
 )
 
 func init() {
@@ -40,18 +58,43 @@ func cilCompatMapFactory() android.Module {
 }
 
 type cilCompatMapProperties struct {
-	// list of source (.cil) files used to build an sepolicy compatibility mapping
-	// file. srcs may reference the outputs of other modules that produce source
-	// files like genrule or filegroup using the syntax ":module". srcs has to be
-	// non-empty.
-	Srcs []string
+	// se_cil_compat_map module representing a compatibility mapping file for
+	// platform versions (x->y). Bottom half represents a mapping (y->z).
+	// Together the halves are used to generate a (x->z) mapping.
+	Top_half *string
+	// list of source (.cil) files used to build an the bottom half of sepolicy
+	// compatibility mapping file. bottom_half may reference the outputs of
+	// other modules that produce source files like genrule or filegroup using
+	// the syntax ":module". srcs has to be non-empty.
+	Bottom_half []string
 }
 
 type cilCompatMap struct {
 	android.ModuleBase
 	properties cilCompatMapProperties
 	// (.intermediate) module output path as installation source.
-	installSource android.OptionalPath
+	installSource android.Path
+}
+
+type CilCompatMapGenerator interface {
+	GeneratedMapFile() android.Path
+}
+
+type dependencyTag struct {
+	blueprint.BaseDependencyTag
+	name string
+}
+
+func expandTopHalf(ctx android.ModuleContext) android.OptionalPath {
+	var topHalf android.OptionalPath
+	ctx.VisitDirectDeps(func(dep android.Module) {
+		depTag := ctx.OtherModuleDependencyTag(dep)
+		switch depTag {
+		case TopHalfDepTag:
+			topHalf = android.OptionalPathForPath(dep.(CilCompatMapGenerator).GeneratedMapFile())
+		}
+	})
+	return topHalf
 }
 
 func expandSeSources(ctx android.ModuleContext, srcFiles []string) android.Paths {
@@ -81,33 +124,62 @@ func expandSeSources(ctx android.ModuleContext, srcFiles []string) android.Paths
 }
 
 func (c *cilCompatMap) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	srcFiles := expandSeSources(ctx, c.properties.Srcs)
+	srcFiles := expandSeSources(ctx, c.properties.Bottom_half)
+
 	for _, src := range srcFiles {
 		if src.Ext() != ".cil" {
-			ctx.PropertyErrorf("srcs", "%s has to be a .cil file.", src.String())
+			ctx.PropertyErrorf("bottom_half", "%s has to be a .cil file.", src.String())
 		}
 	}
 
-	out := android.PathForModuleGen(ctx, c.Name())
+	bottomHalf := android.PathForModuleGen(ctx, "bottom_half")
 	ctx.Build(pctx, android.BuildParams{
 		Rule:   android.Cat,
-		Output: out,
+		Output: bottomHalf,
 		Inputs: srcFiles,
 	})
-	c.installSource = android.OptionalPathForPath(out)
+
+	topHalf := expandTopHalf(ctx)
+	if (topHalf.Valid()) {
+		out := android.PathForModuleGen(ctx, c.Name())
+		ctx.ModuleBuild(pctx, android.ModuleBuildParams{
+			Rule: combineMapsRule,
+			Output: out,
+			Implicits: []android.Path{
+				topHalf.Path(),
+				bottomHalf,
+			},
+			Args: map[string]string{
+				"topHalf": topHalf.String(),
+				"bottomHalf": bottomHalf.String(),
+			},
+		})
+		c.installSource = out
+	} else {
+		c.installSource = bottomHalf
+	}
 }
 
 func (c *cilCompatMap) DepsMutator(ctx android.BottomUpMutatorContext) {
-	android.ExtractSourcesDeps(ctx, c.properties.Srcs)
+	android.ExtractSourcesDeps(ctx, c.properties.Bottom_half)
+	if (c.properties.Top_half != nil) {
+		ctx.AddDependency(c, TopHalfDepTag, String(c.properties.Top_half))
+	}
 }
 
 func (c *cilCompatMap) AndroidMk() android.AndroidMkData {
 	ret := android.AndroidMkData{
-		OutputFile: c.installSource,
+		OutputFile: android.OptionalPathForPath(c.installSource),
 		Class:      "ETC",
 	}
 	ret.Extra = append(ret.Extra, func(w io.Writer, outputFile android.Path) {
 		fmt.Fprintln(w, "LOCAL_MODULE_PATH := $(TARGET_OUT)/etc/selinux/mapping")
 	})
 	return ret
 }
+
+var _ CilCompatMapGenerator = (*cilCompatMap)(nil)
+
+func (c *cilCompatMap) GeneratedMapFile() android.Path {
+	return c.installSource
+}

private/compat/26.0/26.0.ignore.cil

@@ -1,9 +1,11 @@
 ;; new_objects - a collection of types that have been introduced that have no
 ;;   analogue in older policy.  Thus, we do not need to map these types to
 ;;   previous ones.  Add here to pass checkapi tests.
+(type new_objects)
 (typeattribute new_objects)
 (typeattributeset new_objects
-  ( activity_task_service
+  ( new_objects
+    activity_task_service
     adb_service
     adbd_exec
     app_binding_service
@@ -182,8 +184,9 @@
 ;; private_objects - a collection of types that were labeled differently in
 ;;     older policy, but that should not remain accessible to vendor policy.
 ;;     Thus, these types are also not mapped, but recorded for checkapi tests
+(type priv_objects)
 (typeattribute priv_objects)
 (typeattributeset priv_objects
-     ( adbd_tmpfs
-       untrusted_app_27_tmpfs
-     ))
+  ( priv_objects
+    adbd_tmpfs
+    untrusted_app_27_tmpfs))

private/compat/27.0/27.0.ignore.cil

@@ -1,9 +1,11 @@
 ;; new_objects - a collection of types that have been introduced that have no
 ;;   analogue in older policy.  Thus, we do not need to map these types to
 ;;   previous ones.  Add here to pass checkapi tests.
+(type new_objects)
 (typeattribute new_objects)
 (typeattributeset new_objects
-  ( activity_task_service
+  ( new_objects
+    activity_task_service
     adb_service
     app_binding_service
     atrace
@@ -160,5 +162,8 @@
 ;; private_objects - a collection of types that were labeled differently in
 ;;     older policy, but that should not remain accessible to vendor policy.
 ;;     Thus, these types are also not mapped, but recorded for checkapi tests
+(type priv_objects)
 (typeattribute priv_objects)
-(typeattributeset priv_objects (untrusted_app_27_tmpfs))
+(typeattributeset priv_objects
+  ( priv_objects
+    untrusted_app_27_tmpfs))

private/compat/28.0/28.0.ignore.cil

@@ -1,9 +1,11 @@
 ;; new_objects - a collection of types that have been introduced that have no
 ;;   analogue in older policy.  Thus, we do not need to map these types to
 ;;   previous ones.  Add here to pass checkapi tests.
+(type new_objects)
 (typeattribute new_objects)
 (typeattributeset new_objects
-  ( activity_task_service
+  ( new_objects
+    activity_task_service
     adb_service
     app_binding_service
     biometric_service

tests/Android.bp

@@ -63,3 +63,11 @@ python_binary_host {
     required: ["libsepolwrap"],
     defaults: ["py2_only"],
 }
+
+python_binary_host {
+    name: "combine_maps",
+    srcs: [
+        "combine_maps.py",
+        "mini_parser.py",
+    ],
+}

tests/combine_maps.py

@@ -0,0 +1,66 @@
+# Copyright 2018 - The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tool to combine SEPolicy mapping file.
+
+Say, x, y, z are platform SEPolicy versions such that x > y > z. Then given two
+mapping files from x to y (top) and y to z (bottom), it's possible to construct
+a mapping file from x to z. We do the following to combine two maps.
+1. Add all new types declarations from top to bottom.
+2. Say, a new type "bar" in top is mapped like this "foo_V_v<-bar", then we map
+"bar" to whatever "foo" is mapped to in the bottom map. We do this for all new
+types in the top map.
+
+More generally, we can correctly construct x->z from x->y' and y"->z as long as
+y">y'.
+
+This file contains the implementation of combining two mapping files.
+"""
+import argparse
+import re
+from mini_parser import MiniCilParser
+
+def Combine(top, bottom):
+    bottom.types.update(top.types)
+
+    for top_ta in top.typeattributesets:
+        top_type_set = top.typeattributesets[top_ta]
+        if len(top_type_set) == 1:
+            continue
+
+        m = re.match(r"(\w+)_\d+_\d+", top_ta)
+        # Typeattributes in V.v.cil have _V_v suffix, but not in V.v.ignore.cil
+        bottom_type = m.group(1) if m else top_ta
+
+        for bottom_ta in bottom.rTypeattributesets[bottom_type]:
+            bottom.typeattributesets[bottom_ta].update(top_type_set)
+
+    return bottom
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-t", "--top-map", dest="top_map",
+                        required=True, help="top map file")
+    parser.add_argument("-b", "--bottom-map", dest="bottom_map",
+                        required=True, help="bottom map file")
+    parser.add_argument("-o", "--output-file", dest="output_file",
+                        required=True, help="output map file")
+    args = parser.parse_args()
+
+    top_map_cil = MiniCilParser(args.top_map)
+    bottom_map_cil = MiniCilParser(args.bottom_map)
+    result = Combine(top_map_cil, bottom_map_cil)
+
+    with open(args.output_file, "w") as output:
+        output.write(result.unparse())