Re: Debian SID kernel doesn't boot on PowerBook 3400c

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 04/08/2021 à 02:34, Finn Thain a écrit :
> On Tue, 3 Aug 2021, Christophe Leroy wrote:
>
> > Looks like the memory errors are linked to KUAP (Kernel Userspace Access
> > Protection). Based on the places the problems happen, I don't think
> > there are any invalid access, so there must be something wrong in the
> > KUAP logic, probably linked to some interrupts happenning in kernel mode
> > while the KUAP window is opened. And because is not selected by default
> > on book3s/32 until 5.14, probably nobody ever tested it in a real
> > environment before you.
> >
> > I think the issue may be linked to commit
> > https://github.com/linuxppc/linux/commit/c16728835 which happened
> > between 5.12 and 5.13.
>
> The messages, "Kernel attempted to write user page (c6207c) - exploit
> attempt? (uid: 0)", appear in the console logs generated by v5.13. Those
> logs come from the Powerbook G3 discussion in the other thread. Could that
> be the same bug?

Yes, most likely.

So you confirm this appears with 5.13 and not 5.12 ?

Can you check if they happen at commit c16728835
Can you check if they DO NOT happen at preceding commit c16728835~

Could you test without CONFIG_PPC_KUAP
Could you test with CONFIG_PPC_KUAP and CONFIG_PPC_KUAP_DEBUG

Thanks
Christophe