Re: AUTIA authentication sometimes fails

[Peter Maydell]

On Mon, 29 Mar 2021 at 21:07, Derrick McKee <derrick.mckee@gmail.com> wrote:
>
> 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.

cc'ing Richard, but I suspect you'll need to provide more detail...

thanks
-- PMM