They give their customers the source code. If they want to publish it they're legally allowed to do it. It's not as helpful as it seems to get a leaked copy of a massive patch, especially when most upstream work is based on Clang and the most interesting pieces are GCC plugins.
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You could give upstream the latest release of RAP but it wouldn't mean they would understand it and be able to maintain it. It can't simply be merged with no one developing / maintaining it. That is essentially what they did with a few plugins but they're much smaller/simpler.
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RAP was publicly available including the deterministic hash-based forward and backward edge protection. It doesn't really seem like anyone else learned anything from it. The state of the art elsewhere is the much slower Clang CFI which leaves backward edge CFI to something else.
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The backward edge protection is SafeStack, which has issues. There's ways around SafeStack and it's in an incomplete state. It doesn't protect shared objects, only application code.
I've done some work in hbsd to get shared object support working, but my priorities keep shifting
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The shared object support needs tight integration with both the RTLD and libc, in somewhat similar fashion as SSP, but a bit more complex.
If I remember correctly, setjmp/longjmp is still an issue with SafeStack.
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SafeStack wasn't really meant to be used with Clang CFI. It was meant to be used as part of a broader CPI feature which was never finished or landed.
Android started adopting SafeStack including shared object support. It was dropped and it now uses ShadowCallStack instead.
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SafeStack has serious issues with leaks since it uses the main thread stack as the main safe stack but there are assorted pointers to data libc places in it.
Android uses cross-DSO CFI and ShadowCallStack for both the kernel and userspace. ShadowCallStack is arm64 only though.
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It didn't work as intended on x86 since it has stack-based return addresses and they were still returning that way so there was a race. They didn't want to do something more invasive and it wasn't specifically for kernel where they could make stacks inaccessible to other threads.
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arm64 is all that really matters to Android for the foreseeable future. There will be CET on x86 providing hardware shadow stack support and arm64 will be able to use ARMv8.5 / ARMv9 MTE (memory tagging) to make ShadowCallStack more secure if they decide to figure that out.
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Good luck finding stuff that uses PA and MTE extension on the Android side of things
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Android 12 has support for memory tagging, BTI and PAC. Nearly all available hardware is still ARMv8.2 so it was developed and tested primarily with QEMU. I don't know what you mean about good luck finding stuff. I'm not aware of any product that has shipped with MTE support yet.
On a related tangent: I wish there was actual, tangible cost-effective (yet performant) ARM64 development hardware out there.
I would love to just go to a Microcenter and buy ARM64 desktop parts just like I can with AMD64.
Even better if it was ARMv8.5 and above.
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Keep in mind that as can be seen from iPhones, ARMv8.5 / ARMv9 don't imply having support for MTE. If MTE is included for the in-house Cortex cores, then it will end up being broadly supported. If it's not included or if it's an optional variant of them it will be a rare feature.
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