Re: [tip: x86/urgent] x86/mm: Fix pti_clone_entry_text() for i386

[Guenter Roeck]

On 8/6/24 08:59, Peter Zijlstra wrote:
> On Tue, Aug 06, 2024 at 05:46:53PM +0200, Peter Zijlstra wrote:
> > On Tue, Aug 06, 2024 at 05:05:15PM +0200, Peter Zijlstra wrote:
> > > On Tue, Aug 06, 2024 at 04:56:32PM +0200, Peter Zijlstra wrote:
> > > > On Tue, Aug 06, 2024 at 07:25:42AM -0700, Guenter Roeck wrote:
> > > >
> > > > > I created http://server.roeck-us.net/qemu/x86-v6.11-rc2/ with all
> > > > > the relevant information. Please let me know if you need anything else.
> > > >
> > > > So I grabbed that config, stuck it in the build dir I used last time and
> > > > upgraded gcc-13 from 13.2 ro 13.3. But alas, my build runs successfully
> > > > :/
> > > >
> > > > Is there anything else special I missed?
> > >
> > > run.sh is not exacrlty the same this time, different CPU model, that
> > > made it go.
> > >
> > > OK, lemme poke at this.
> >
> > Urgh, so crypto's late_initcall() does user-mode-helper based modprobe
> > looking for algorithms before we kick off /bin/init :/
> >
> > This makes things difficult.
> >
> > Urgh.
>
> So the problem is that mark_readonly() splits a code PMD due to NX. Then
> the second pti_clone_entry_text() finds a kernel PTE but a user PMD
> mapping for the same address (from the early clone) and gets upset.
>
> And we can't run mark_readonly() sooner, because initcall expect stuff
> to be RW. But initcalls do modprobe, which runs user crap before we're
> done initializing everything.
>
> This is a right mess, and I really don't know what to do.

And there was me thinking this one should be easy to solve. Oh well.

Maybe Linus has an idea ? I am getting a bit wary to reporting all those
weird problems to him, though.

Guenter