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

Chris Metcalf
2015-09-28T21:54:59Z

On 09/28/2015 04:54 PM, Andy Lutomirski wrote:
> On Mon, Sep 28, 2015 at 11:17 AM, Chris Metcalf <cmetcalf-d5a29ZRxExrQT0dZR+AlfA@public.gmane.org> 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-d5a29ZRxExrQT0dZR+AlfA@public.gmane.org>
>> ---
>> 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