This is an issue that allows unentitled root to read kernel frame
pointers, which might be useful in combination with a kernel memory
corruption bug.
By design, the syscall stack_snapshot_with_config() permits unentitled
root to dump information about all user stacks and kernel stacks.
While a target thread, along with the rest of the system, is frozen,
machine_trace_thread64() dumps its kernel stack.
machine_trace_thread64() walks up the kernel stack using the chain of
saved RBPs. It dumps the unslid kernel text pointers together with
unobfuscated frame pointers.
The attached PoC dumps a stackshot into the file stackshot_data.bin
when executed as root. The stackshot contains data like this:
00000a70 de 14 40 00 80 ff ff ff a0 be 08 77 80 ff ff ff |..@........w....|
00000a80 7b b8 30 00 80 ff ff ff 20 bf 08 77 80 ff ff ff |{.0..... ..w....|
00000a90 9e a6 30 00 80 ff ff ff 60 bf 08 77 80 ff ff ff |..0.....`..w....|
00000aa0 5d ac 33 00 80 ff ff ff b0 bf 08 77 80 ff ff ff |].3........w....|
The addresses on the left are unslid kernel text pointers; the
addresses on the right are valid kernel stack pointers.
This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.
