[PATCH 3/4] Revert "ARM: mmu: use client domain permissions to support ARMv7 eXecute Never"

[Ahmad Fatoum]

Hi Peter,

On 19.09.21 09:50, Peter Rosin wrote:
> On 2021-09-19 09:06, Rouven Czerwinski wrote:
>> Hi Peter,
>>
>> while this may break for your board, it fundamentally introduces the
>> possibility to speculate out of the RAM area on speculation happy
> 
> I'm aware of that. For me, speculation is not an issue since *any*
> rogue code running on the embedded device in question is a major fail.

We have seen Cortex-A7 CPUs speculatively executing I/O memory. That's
why we mar everything eXecute-Never except for known memory banks and
expect board code to mark any further regions that are safe to execute
manually. 

> Also, from the cover letter:
> 
> "I'm going to follow up with patches. I very much realize that
> these patches are most likely not acceptable as-is, but I do
> include them since they are probably the best description of
> where the problems are."
> 
>> processors. Are you calling into SAMA5D3 ROM code somewhere? If so an
> 
> *I* am not calling anything. Maybe the board code for sama5d3xek is,
> but I have no idea as it's not "my" code. How can I figure out if it
> does?

If you don't revert this patch. Do you get any output at all?
If not, enable DEBUG_LL and see how far you get before hanging.

Cheers,
Ahad

> 
> Cheers,
> Peter
> 
>> exception can be added similar to the handling for the HAB code
>> (arch/arm/cpu/mmu_early.c):
>>
>> 	if (IS_ENABLED(CONFIG_HABV4) && IS_ENABLED(CONFIG_ARCH_IMX6))
>> 		map_region(0x0, SZ_1M, PMD_SECT_DEF_CACHED);
>>
>> which allows calls into the NXP boot ROM to retrieve the HAB status.
> 
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