[PATCH v3 2/8] elf: Add a tunable to control use of tagged memory

[Richard Earnshaw]

On 27/11/2020 14:52, H.J. Lu via Libc-alpha wrote:
> On Thu, Nov 26, 2020 at 6:45 PM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 11/26/20 10:49 PM, H.J. Lu wrote:
>>> The first few questions are
>>
>> OK this is a good start:
>>
>>> 1.  Where should binary markers be checked?
>>
>> At early startup alongside the cpu features resolution.  We enable
>> tagging if the CPU supports MTE and the marker is set.
> 
> We won't know all the issues before we implement it.
> 
>>> 2.  How should binary marker checking work together with tunables?
>>
>> The presence of a binary marker enables tagging and a tunable should not
>> be able to disable it.  The exception would be systemwide tunables[1]
>> where administrators could set sweeping policies for their systems,
>> including disabling tagging systemwide if needed.
> 
> The memory tag implementation should be independent of tunables.
> Tunables should just turn on and off a few bits in the memory tag
> implementation.  Make the memory tag implementation depend on
> tunables seems wrong to me.

That shouldn't matter.  The tunables are documented as not being stable
and nothing else is exposed to the user; so if we want to change things
later, there's nothing to stop that.

R.

> 
>> If binary marker is not present, tunables behave the way it is proposed
>> in the patchset.
>>
>> Siddhesh
>>
>> [1] Vapourware alert!
> 
> 
>