AUTIA authentication sometimes fails

[Derrick McKee]

Hi,

I am running across a scenario where a PAC signed code pointer (using
pacia) sometimes does not successfully authenticate despite the signed
pointer and the salt used to sign the pointer are correctly given to a
autia instruction.  Only one particular pointer fails, while others
are correctly authenticated.  Unfortunately, I can't provide a simple
use case, because the behavior is part of a running kernel, and all
the pointers involved are kernel space pointers.  An example of what I
am seeing (not guaranteeing correct assembly, just a gist):

mov x9, 0xffff800009200000
mov x10, 0x20001
pacia x9, x10  // x9 contains 0xff90800009200000
...
mov x9, 0xff90800009200000
mov x10 0x20001
autia x9, x10  // x9 contains invalid pointer

However, this same code with different pointer values correctly
authenticate.  Is there something specific about the kernel and PAC
authentication that I am missing?  Thanks.

-- 
Derrick McKee
Phone: (703) 957-9362
Email: derrick.mckee@gmail.com