Re: [Qemu-devel] [PATCH] seccomp: allow sched_setscheduler() with SCHED_IDLE policy

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jul 11, 2018 at 04:48:55PM +0200, Eduardo Otubo wrote:
> On 10/07/2018 - 16:55:57, Marc-André Lureau wrote:
> > Current and upcoming mesa releases rely on a shader disk cash. It uses
> > a thread job queue with low priority, set with
> > sched_setscheduler(SCHED_IDLE). However, that syscall is rejected by
> > the "resourcecontrol" seccomp qemu filter.
> > 
> > Since it should be safe to allow lowering thread priority, let's allow
> > scheduling thread to idle policy.
> > 
> > Related to:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1594456
> > 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  qemu-seccomp.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/qemu-seccomp.c b/qemu-seccomp.c
> > index 148e4c6f24..9cd8eb9499 100644
> > --- a/qemu-seccomp.c
> > +++ b/qemu-seccomp.c
> > @@ -34,6 +34,12 @@
> >  struct QemuSeccompSyscall {
> >      int32_t num;
> >      uint8_t set;
> > +    uint8_t narg;
> > +    const struct scmp_arg_cmp *arg_cmp;
> > +};
> > +
> > +const struct scmp_arg_cmp sched_setscheduler_arg[] = {
> > +    SCMP_A1(SCMP_CMP_NE, SCHED_IDLE)
> >  };
> >  
> >  static const struct QemuSeccompSyscall blacklist[] = {
> > @@ -92,7 +98,8 @@ static const struct QemuSeccompSyscall blacklist[] = {
> >      { SCMP_SYS(setpriority),            QEMU_SECCOMP_SET_RESOURCECTL },
> >      { SCMP_SYS(sched_setparam),         QEMU_SECCOMP_SET_RESOURCECTL },
> >      { SCMP_SYS(sched_getparam),         QEMU_SECCOMP_SET_RESOURCECTL },
> > -    { SCMP_SYS(sched_setscheduler),     QEMU_SECCOMP_SET_RESOURCECTL },
> > +    { SCMP_SYS(sched_setscheduler),     QEMU_SECCOMP_SET_RESOURCECTL,
> > +      ARRAY_SIZE(sched_setscheduler_arg), sched_setscheduler_arg },
> >      { SCMP_SYS(sched_getscheduler),     QEMU_SECCOMP_SET_RESOURCECTL },
> >      { SCMP_SYS(sched_setaffinity),      QEMU_SECCOMP_SET_RESOURCECTL },
> >      { SCMP_SYS(sched_getaffinity),      QEMU_SECCOMP_SET_RESOURCECTL },
> > @@ -118,7 +125,8 @@ static int seccomp_start(uint32_t seccomp_opts)
> >              continue;
> >          }
> >  
> > -        rc = seccomp_rule_add(ctx, SCMP_ACT_KILL, blacklist[i].num, 0);
> > +        rc = seccomp_rule_add_array(ctx, SCMP_ACT_KILL, blacklist[i].num,
> > +                                    blacklist[i].narg, blacklist[i].arg_cmp);
> >          if (rc < 0) {
> >              goto seccomp_return;
> >          }
> > -- 
> > 2.18.0.129.ge3331758f1
> > 
> 
> Acked-by: Eduardo Otubo <otubo@redhat.com>
> 
> Patch looks safe enough for me. If everyone else is OK with this I'll send a
> pull-request tomorrow morning.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>



Regards,
Daniel
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