Re: Strange switching [threadname] to secondary mode after exception #0 in kernel-space at 0x80272444

["François Legal" <devel@thom.fr.eu.org>]

Anybody can help on this ?

François

Le Mercredi, Septembre 30, 2020 17:14 CEST, François Legal via Xenomai <xenomai@xenomai.org> a écrit:

> So the problem here lies in the calls to rtnet_get_arg(fd, &_msg, msg, sizeof(*msg)); in af_packet.c sendmasg/recvmsg
>
> The only explanation I could find was that, for my architecture (32bit ARMv7), syscall use the COBALT_SYSCALL32emu variants for sendmsg/recvmsg calls, which in turn allocate a struct user_msghdr on the SVC stack, then calls rt_packet_sendmsg/rt_packet_recvmsg with the address of that struct.
>
> Then, rtnet_get_arg would invoke arm_copy_from_user, which, with SPECTRE mitigation turned on (you normally can't disable this by configuration), would check that the source pointer is in the userland memory area, and hence fail in my case.
>
> Going from there, except disabling SPECTRE mitigation, I'm not sure how I can fix this.
>
> François
>
> Le Mercredi, Septembre 30, 2020 10:48 CEST, François Legal via Xenomai <xenomai@xenomai.org> a écrit:
>
> > I might have found what is causing this problem : CONFIG_CPU_SPECTRE
> >
> > It was the noticeable difference between my last (4.4.189) kernel release not showing this problem, and the next I tried (4.4.227).
> > If I modify the Kconfig to disable CPU_SPECTRE, the problem does not show up anymore.
> >
> > I'll dig a little deeper into that now.
> >
> > François
> >
> > Le Mercredi, Septembre 30, 2020 08:42 CEST, François Legal <francois.legal@thom.fr.eu.org> a écrit:
> >
> > > So I decided to dig a little deeper in this problem, and found out that it is not xenomai3.1 specific.
> > > I tried with xenomai-3.0.9 and linux 4.4.227 -> same problem.
> > > I thought it might be a matter of ipipe patch not quite fit to 4.4.227, so I decided to try with latest ipipe-4.4.y-cip from git and xenomai 3.0.9, but the same problem happens.
> > >
> > > François
> > >
> > > Le Vendredi, Septembre 25, 2020 18:11 CEST, François Legal via Xenomai <xenomai@xenomai.org> a écrit:
> > >
> > > > Sorry to come back so late on that topic.
> > > > I took some time to write a simple test program, which is attached.> >
> > > > Config is as follows :
> > > > xenomai-3.1
> > > > linux-4.4.227
> > > >
> > > > François
> > > >
> > > > Le Vendredi, Août 21, 2020 20:04 CEST, Jan Kiszka <jan.kiszka@siemens.com> a écrit:
> > > >
> > > > > On 20.08.20 15:46, François Legal via Xenomai wrote:
> > > > > > Using RTNet with multiple interfaces, xenomai 3.1 with linux 4.4
> > > > > > Whenever a posix RT thread calls recvmsg (), I get this error.
> > > > > >
> > > > > > I could track this down to line 422 in udp.c :     msg = rtnet_get_arg(fd, &_msg, u_msg, sizeof(_msg));
> > > > > >
> > > > > > If I disassemble the kernel, the failing instruction (at 0x80272444) is a nop in arm_copy_from_user
> > > > > > Am I doing anything wrong ?
> > > > >
> > > > > Maybe you are passing an invalid pointer to recvmsg, directly or in its
> > > > > message structures. That would cause an exception which is fixed up but
> > > > > also reported. Do you get an error in return?
> > > > >
> > > > > Jan
> > > > >
> > > > > --
> > > > > Siemens AG, Corporate Technology, CT RDA IOT SES-DE
> > > > > Corporate Competence Center Embedded Linux
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