text stringlengths 0 1.99k |
|---|
tools and techniques will need to be adjusted specifically for it. |
(Shoutout to Androguard development picking up after a dry spell!) |
To avoid maintaining special Dalvik tooling, some tools opt to transpile |
Dalvik bytecode into a form usable by tools with a larger audience, such as |
dex2jar used by SootUP [8]. Its predecessor, Soot, is used by SimiDroid. |
Unfortunately, Dalvik is not Java. It has a hard limitation on the number |
of identifiers in a single DEX file, so tools need to be able to merge |
those. It's no big deal nowadays. However, Dalvik does not impose an upper |
limit on the number of instructions in a method, so if it is lifted to Java |
bytecode, certain functions must be split because they contain more than |
65536 bytes, which Java bytecode forbids. This was an open issue that |
crashes Soot (and thus SimiDroid) and, for a while, caused SootUP to skip |
analyzing a method. While the upstream dex2jar has fixed the issue [17], |
SootUP removed this dependency and integration is left as an exercise to |
the reader. Also, there might still be a way to break analysis with large |
methods `:)`. |
---[ 2.4 - Summary and Back to Binary |
To summarize, tools to compute similarity don't work well with modern |
Android apps. Optimizations are having an overly obfuscating effect, and |
Dalvik-based tools have trouble keeping up to date. So what are our |
options? What do other fields do to meet their similarity needs? Turns out: |
Rop Gadgets^W^W BinDiff is forever [9] (and now open source!). Let's leave |
Dalvik be and compile apps to their binary OAT version using the ARTs |
ahead-of-time compilation. Since these binaries are valid ELF files, we can |
feed them to a disassembler, create a BinExport [13] file, and then feed it |
further to halvarflake's friendly neighborhood diffing tool based on |
graph-isomorphism [10]. |
--[ 3 - A Bit of Examples |
> What is a function? A miserable little pile of bytes. |
Let's go over some questions you might have by now. We've tried all this on |
a Pixel 8 hardware phone running Android 15 (BP1A.250305.019) just to show |
off this works on real devices, but an emulator works just as well. Since |
the system owns the system-generated OAT files, we need root to access |
them. Our test app will be Organic Maps [11] (version 2025.05.20-5-FDroid) |
because we just think it's neat and more people should know about it. |
---[ 3.1 - How Does the ART Compile an App's Code Ahead-of-Time? |
The ART is supposed to run AOT compilation during installation, and dex2oat |
is part of the art, so let's start logcat with `adb logcat artd:I *:S` and |
install an app. |
```console |
$ adb install app.organicmaps.apk |
Performing Streamed Install |
Success |
``` |
In the logcat output, we see the complete invocation of dex2oat: |
```console |
$ adb logcat artd:I *:S # formatted for convenience |
[...] |
02-29 13:37:42.123 6074 6074 I artd : Running dex2oat: |
/apex/com.android.art/bin/art_exec --drop-capabilities |
--set-task-profile=Dex2OatBootComplete --set-priority=background |
--keep-fds=6:7:8:9:10:11 -- |
/apex/com.android.art/bin/dex2oat64 |
--zip-fd=6 --zip-location=/data/app/[...]/base.apk |
--oat-fd=7 --oat-location=/data/app/[...]/oat/arm64/base.odex |
--output-vdex-fd=8 --swap-fd=9 --class-loader-context-fds=10:11 |
--class-loader-context=PCL[]{PCL[...]} |
--classpath-dir=/data/app/[...] --instruction-set=arm64 |
--instruction-set-features=default |
--instruction-set-variant=cortex-a55 |
--compiler-filter=verify |
--compilation-reason=install --compact-dex-level=none |
--max-image-block-size=524288 --resolve-startup-const-strings=true |
--generate-mini-debug-info --runtime-arg -Xtarget-sdk-version:35 |
--runtime-arg -Xhidden-api-policy:enabled --cpu-set=0,1,2,3,4,5,6,7,8 |
-j8 --runtime-arg -Xms64m --runtime-arg -Xmx512m |
--comments=app-name:app.organicmaps,[...] |
``` |
There's a lot in there, and `dex2oat --help` makes for a lovely afternoon |
read. But we'd like to point out some interesting things. The obvious one |
is that it's just a binary that we can call ourselves. Sure, there is some |
trickery with file descriptors, but the flag `--dex-file` accepts a DEX, |
JAR, or APK. Second, the flag `--compiler-filter` is used to verify the |
code, creating the .vdex file. It also accepts 'everything', which is |
nothing more than the full-AOT mode of Android 7 and 8. |
Because the system didn't use a profile for this compilation, the resulting |
odex is quite small: |
```console |
$ adb shell pm path app.organicmaps |
package:/data/app/~~ICLdeF7FOXIe1b9MxToZGQ==/app.organicmaps-2xFay0QEb95pHRC |
_k_T1gA==/base.apk |
$ adb shell ls -lah |
/data/app/~~ICLdeF7FOXIe1b9MxToZGQ==/app.organicmaps-2xFay0QEb95pHRC_k_T1gA= |
=/oat/arm64/base.odex |
-rw-r--r-- 1 system all_a306 65K 2025-02-29 13:37 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.