Add ARM MTE Support - May be broken

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This is the start of MTE support in IsoAlloc. Most of the code is adapted from Scudo (also released under an Apache v2 license with minor modifications). It is UNTESTED at the moment and should not be merged. If you have a Pixel 8 and want to do some testing of this PR please get in touch with me.

[jvoisin]

cc @muhomorr @strcat

[jvoisin]

This should go in a read-only zone I think, otherwise, MTE is disableable by an attacker with an arbitrary write primitive.

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A read-only section for settings like this is easy to implement but often requires dereferencing both _root and ro_config_page which can flush the cache and really hurt performance in any hot paths.

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This PR looks OK to merge behind the ARM_MTE build define which is disabled by default. Its mostly complete and tested using qemu. However I have little faith in the qemu implementation as I ran into several bugs involving memset() of PROT_MTE pages that don't appear to happen with a simple while(){write()} loop. Once I get access to a real device with MTE support I will retest this functionality.

TLDR: YMMV, please let me know if you can test this on real hardware!

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If you want to test in an Ubuntu Docker container on an M1/M2 based Macbook just enabled the ARM_MTE build defines in Makefile (make sure to set DISABLE_CANARY=1 as well).

apt-get install clang-12 make qemu qemu-system-arm qemu-user-static
make mte_test

The make command above will compile test programs and just runs the following command:

qemu-aarch64-static -cpu max build/tests

If you add -strace to the qemu command you should be able to see it killed with the proper signal and si_code for SEGV_MTESERR.

--- SIGSEGV {si_signo=SIGSEGV, si_code=9, si_addr=0x0e00005501a15400} ---
qemu: uncaught target signal 11 (Segmentation fault) - core dumped