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

On 09/28/2015 04:54 PM, Andy Lutomirski wrote:

On Mon, Sep 28, 2015 at 11:17 AM, Chris Metcalf [off-list ref] wrote:

quoted

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 <redacted>
---
  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.

quoted

+       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