Re: [PATCH v7 04/11] task_isolation: provide strict mode configurable signal

[Chris Metcalf]

On 09/28/2015 04:54 PM, Andy Lutomirski wrote:
> On Mon, Sep 28, 2015 at 11:17 AM, Chris Metcalf <cmetcalf@xxxxxxxxxx> wrote:
> > Allow userspace to override the default SIGKILL delivered
> > when a task_isolation process in STRICT mode does a syscall
> > or otherwise synchronously enters the kernel.
> >
> > In addition to being able to set the signal, we now also
> > pass whether or not the interruption was from a syscall in
> > the si_code field of the siginfo.
> >
> > Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> > ---
> >   include/uapi/linux/prctl.h |  2 ++
> >   kernel/isolation.c         | 17 +++++++++++++----
> >   2 files changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> > index 2b8038b0d1e1..a5582ace987f 100644
> > --- a/include/uapi/linux/prctl.h
> > +++ b/include/uapi/linux/prctl.h
> > @@ -202,5 +202,7 @@ struct prctl_mm_map {
> >   #define PR_GET_TASK_ISOLATION          49
> >   # define PR_TASK_ISOLATION_ENABLE      (1 << 0)
> >   # define PR_TASK_ISOLATION_STRICT      (1 << 1)
> > +# define PR_TASK_ISOLATION_SET_SIG(sig)        (((sig) & 0x7f) << 8)
> > +# define PR_TASK_ISOLATION_GET_SIG(bits) (((bits) >> 8) & 0x7f)
> >
> >   #endif /* _LINUX_PRCTL_H */
> > diff --git a/kernel/isolation.c b/kernel/isolation.c
> > index 3779ba670472..44bafcd08bca 100644
> > --- a/kernel/isolation.c
> > +++ b/kernel/isolation.c
> > @@ -77,14 +77,23 @@ void task_isolation_enter(void)
> >          }
> >   }
> >
> > -static void kill_task_isolation_strict_task(void)
> > +static void kill_task_isolation_strict_task(int is_syscall)
> >   {
> > +       siginfo_t info = {};
> > +       int sig;
> > +
> >          /* RCU should have been enabled prior to this point. */
> >          RCU_LOCKDEP_WARN(!rcu_is_watching(), "kernel entry without RCU");
> >
> >          dump_stack();
> >          current->task_isolation_flags &= ~PR_TASK_ISOLATION_ENABLE;
> > -       send_sig(SIGKILL, current, 1);
> > +
> > +       sig = PR_TASK_ISOLATION_GET_SIG(current->task_isolation_flags);
> > +       if (sig == 0)
> > +               sig = SIGKILL;
> > +       info.si_signo = sig;
> > +       info.si_code = is_syscall;
> I think this needs real SI_ defines.

Yeah, it's a fair point, but of course SIGKILL has no SI_ defines
at all right now.  I'm tempted to suggest we just back out setting
si_code altogether.  It might be worth a one-line console message
(a la show_signal_message()), and use that to pack in the extra
information, instead of trying to fuss with the siginfo data.

> > +       send_sig_info(sig, &info, current);
> >   }
> >
> >   /*
> > @@ -103,7 +112,7 @@ void task_isolation_syscall(int syscall)
> >
> >          pr_warn("%s/%d: task_isolation strict mode violated by syscall %d\n",
> >                  current->comm, current->pid, syscall);
> > -       kill_task_isolation_strict_task();
> > +       kill_task_isolation_strict_task(1);
> No magic numbers please.

I think mooted by the above, but, good point.

--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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