Re: Regression between 6.1.135 and 6.1.139, possibly related to ITS mitigations

["Moritz Mühlenhoff" <mmuhlenhoff@wikimedia.org>]

Am Wed, May 21, 2025 at 11:24:52PM +0200 schrieb Alexandre Chartre:
> 
> > > On Linux 6.1.135 every works fine with both the 20250211 and
> > > 20250512 microcode releases (kern.log is attached as
> > > 6.1.135-feb-microcode.log and 6.1.135-may-microcode.log)
> > > 
> > > With 6.1.139 and the February microcode, oopses appear related
> > > to clear_bhb_loop() (which may be related to "x86/its: Align
> > > RETs in BHB clear sequence to avoid thunking"?). This is
> > > captured in 6.1.139-feb-microcode.log.
> > > 
> > > With 6.1.139 and the May microcode, the system mostly
> > > crashes on bootup (in my tests it crashed in three out of
> > > four attempts). I've captured both the crash
> > > (6.1.139-may-microcode-crash.log) and a working boot
> > > (6.1.139-may-microcode-noncrash.log).
> > > 
> > > If you need any additional information, please let me know!
> > 
> > After looking at your crash logs in more detail, I suspect that your
> > issue is the same root cause as spotted as well for the 5.15 series in
> > https://lore.kernel.org/all/81cd1d38-8856-4b27-921d-839d9e385942@oracle.com/
> > 
> > I assume you can confirm as well that disabling the ITS mitigation
> > with indirect_target_selection=off makes the system boot?
> > 
> > Regards,
> > Salvatore
> 
> And this should be fixed by this patch:
> 
> x86/modules: Set VM_FLUSH_RESET_PERMS in module_alloc()

Confirmed: Running 6.1.139 plus "x86/modules: Set VM_FLUSH_RESET_PERMS
in module_alloc()" resolves the issue: I've rebooted the affected server
four times with a custom build and the oopses are gone and it reboots
reliably.

Cheers,
        Moritz