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81 lines
2.3 KiB
81 lines
2.3 KiB
4 months ago
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# Microdroid Payload
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Payload disk is a composite disk referencing host APEXes and an APK so that microdroid
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reads activates APEXes and executes a binary within the APK.
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## Format
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Payload disk has 1 + N(number of APEX/APK payloads) partitions.
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The first partition is a Microdroid Signature partition which describes other partitions.
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And APEXes and an APK are following as separate partitions.
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For now, the order of partitions are important.
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* partition 1: Microdroid Signature
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* partition 2 ~ n: APEX payloads
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* partition n + 1: APK payload
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It's subject to change in the future, though.
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### Microdroid Signature
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Microdroid Signature contains the signatures of the payloads so that the payloads are
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verified inside the Guest OS.
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Microdroid Signature is composed of header and body.
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| offset | size | description |
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|--------|------|----------------------------------------------------------------|
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| 0 | 4 | Header. unsigned int32: body length(L) in big endian |
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| 4 | L | Body. A protobuf message. [schema](microdroid_signature.proto) |
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### Payload Partitions
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At the end of each payload partition the size of the original payload file (APEX or APK) is stored
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in 4-byte big endian.
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For example, the following code shows how to get the original size of host apex file
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when the apex is read in microdroid as /dev/block/vdc2,
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int fd = open("/dev/block/vdc2", O_RDONLY | O_BINARY | O_CLOEXEC);
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uint32_t size;
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lseek(fd, -sizeof(size), SEEK_END);
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read(fd, &size, sizeof(size));
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size = betoh32(size);
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## How to Create
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### `mk_payload`
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`mk_payload` creates a payload image.
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```
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$ cat payload_config.json
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{
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"system_apexes": [
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"com.android.adbd",
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],
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"apexes": [
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{
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"name": "com.my.hello",
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"path": "hello.apex"
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}
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],
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"apk": {
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"name": "com.my.world",
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"path": "/path/to/world.apk"
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}
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}
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$ adb push payload_config.json hello.apex /data/local/tmp/
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$ adb shell 'cd /data/local/tmp; /apex/com.android.virt/bin/mk_payload payload_config.json payload.img
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$ adb shell ls /data/local/tmp/*.img
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payload.img
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payload-footer.img
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payload-header.img
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payload-signature.img
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payload.img.0 # fillers
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payload.img.1
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...
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```
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In the future, [VirtManager](../../virtmanager) will handle this.
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