spectre-armv7
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cryptax
This is an attempt to implement Spectre on ARMv7
Attempt of implementation of Spectre for ARMv7A
This is an attempt to implement a Proof of Concept of Spectre on ARMv7-based Android smartphones, re-using lots of input from various prior research (see source code header).
This Proof of Concept is derived from the one presented in the paper. It isn't malicious (it reveals a password hidden in the same process). Use it responsibly.
References
- Spectre paper
- Spectre PoC from the paper
- Implementation of Spectre for AArch64
- Libflush from ARMageddon
Run
Pre-requisites
- Android NDK
- Android SDK Platform packages (see here)
- Linux 64bits - if you not you'll need to tweak the compiler path in the
Makefile.
Compile
Edit the Makefile and update:
ANDROID_NDK: provide the path to your Android NDK root directoryANDROID_PLATFORM: provide the name of your Android platform version. For exampleandroid-22.
Then:
$ make
Run
Connect a smartphone (or an emulator).
Make sure it is seen by adb devices.
Then, do make run to copy the executable onto your smartphone and run it (with no arguments).
If you wish to run the program with arguments, then you need to push the executable to your smartphone adb push executable /data/local/tmp, open a shell adb shell and then run the executable with arguments.
Please have a look at the source code for arguments :)
Options
I have implemented several different ways to measure time. Select the one you wish by changing TFLAGS in the Makefile or by specifying it as make argument:
$ make TFLAGS=-DTIMING_REGISTER all
| TFLAGS value | Description |
|---|---|
| -DTIMING_POSIX | Uses the POSIX function clock_gettime() |
| -DTIMING_PTHREAD | Uses a dedicated thread counter |
| -DTIMING_PERFEVENT | Uses the Performance Monitoring Unit |
| -DTIMING_REGISTER | Uses the Performance Monitor Control Register |
| -DTIMING_LIBFLUSH | Uses Libflush. Mainly if you do not trust my implementation and want to check with another one :) |
To use Libflush, you must
- Download and compile it. See instructions in libflush. With NDK 17, the following patch must be applied to be able to compile:
$ git diff config-arm.mk
diff --git a/libflush/config-arm.mk b/libflush/config-arm.mk
index 7666fa9..81f1976 100644
--- a/libflush/config-arm.mk
+++ b/libflush/config-arm.mk
@@ -6,7 +6,7 @@ ANDROID_SYSROOT = ${ANDROID_NDK_PATH}/platforms/${ANDROID_PLATFORM}/arch-arm
ANDROID_CC = ${ANDROID_TOOLCHAIN_BIN}/arm-linux-androideabi-gcc
ANDROID_CC_FLAGS = --sysroot=${ANDROID_SYSROOT}
-ANDROID_INCLUDES = -I ${ANDROID_NDK_PATH}/platforms/${ANDROID_PLATFORM}/arch-arm/usr/include
+ANDROID_INCLUDES = -I ${ANDROID_NDK_PATH}/sysroot/usr/include -I ${ANDROID_NDK_PATH}/sysroot/usr/include/arm-linux-androideabi/
ANDROID_CFLAGS = ${ANDROID_INCLUDES} -march=armv7-a -fPIE
ANDROID_LDFLAGS = ${ANDROID_INCLUDES} -march=armv7-a -fPIE
- Copy the include file
libflush.hand the compiledlibflush.ainto this directory - Compile with option
-DTIMING_LIBFLUSH
Results on ARMv7 based Android smartphones
Those results apply to a smartphone with ARM Cortex A53 cores. Those cores are seen as ARMv7 (I guess because the ROM does not have 64-bit enabled). I compiled with Android NDK r13b and platform 22 (Android 5.1). More recently, I compiled with Android NDK r17 and platform 22.
| CPU | TIMING | MAX_TRIES | CACHE_HIT_THRESHOLD | Results |
|---|---|---|---|---|
| Cortex A8 | PTHREAD | 999 | 80 | Too many cache hits |
| Cortex A8 | PTHREAD | 5500 | 1 | Still too many cache hits! |
| Cortex A8 | POSIX | 999 | 80 | Unclear, probably too many cache hits |
| Cortex A8 | POSIX | 999 | 1 | Unclear |
| Cortex A8 | PERFEVENT | 999 | 80 | No perf event interface |
| Cortex A8 | REGISTER | 999 | 80 | Illegal instruction |
| Cortex A8 | LIBFLUSH with POSIX | 999 | 80 | find_congruent_addresses: assertion "found == ADDRESS_COUNT" failed and Segmentation fault |
| Cortex A8 | LIBFLUSH with PTHREAD | 999 | 80 | find_congruent_addresses: assertion "found == ADDRESS_COUNT" failed and Segmentation fault |
| Cortex A8 | LIBFLUSH with Register | 999 | 80 | Illegal instruction |
| Cortex A8 | LIBFLUSH with PERFEVENT | 999 | 80 | No perf event interface |
| Cortex A53 | LIBFLUSH with cache eviction and POSIX and custom DEVICE_CONFIGURATION | 999 | 80 | find_congruent_addresses: assertion "found == ADDRESS_COUNT" |
| Cortex A53 | PTHREAD | 999 | 80 | too many cache hits. Decrease threshold below 5 |
| Cortex A53 | PTHREAD | 5500 | 1 | Unclear. Still too many cache hits! |
| Cortex A53 | PTHREAD | 2500 | 4 | Unclear. The correct character is a cache hit, but so are several others... |
| Cortex A53 | POSIX | 999 | 80 | No cache hit recorded. Increase threshold around 500 |
| Cortex A53 | POSIX | 5500 | 380 | Unclear |
| Cortex A53 | REGISTER | Illegal instruction Configuring PMUSERENR: probably won't work! |
||
| Cortex A53 | PERFEVENT | No perf event interface |
Conclusion / status
- Perf event is not working on my devices.
- Register cannot work as such. PMU must be enabled via a kernel module. I haven't done this yet.
- I get the same results with Libflush or with my own implementation - which is basically just to check my own implementation is correct.
- Dedicated thread seems unprecise.
clock_getttime()gives the best results, but yet unable to recover the secret. Not sure if it's bad configuration, bad luck, or just that the device is not vulnerable to Spectre.
cryptax