On 8/10/2016 3:52 AM, Andy Lutomirski wrote:
On Aug 9, 2016 11:30 PM, "Chris Metcalf" <cmetc...@mellanox.com> wrote:
@@ -91,6 +92,15 @@ static long syscall_trace_enter(struct pt_regs *regs)
if (emulated)
return -1L;
+ /* In isolation mode, we may prevent the syscall from running. */
+ if (work & _TIF_TASK_ISOLATION) {
+ if (task_isolation_syscall(regs->orig_ax) == -1) {
+ regs->orig_ax = -1;
+ return 0;
+ }
+ work &= ~_TIF_TASK_ISOLATION;
+ }
+
What is this? It's not mentioned in the changelog. It seems
nonsensical to me. If nothing else, you forgot to update regs->ax,
but I don't even know what you're trying to do.
It's mentioned in the changelog as "Fixes a bug in x86 syscall_trace_enter()
[seen by Francis Giraldeau]." To be fair, I didn't hear back from Francis, and
you're right, this doesn't look like it makes any sense now. (I've added him
to the cc's on this email; for this series I had just put him on the cover
letter.)
I modeled this code on a snippet from the old two-phase syscall entry work:
if (ret == SECCOMP_PHASE1_SKIP) {
regs->orig_ax = -1;
ret = 0;
}
You got rid of this during the 4.7-rc series, but my code above was at least
plausibly valid until then :-)
Regardless, I assume that the right thing for that condition to do now when
it triggers is to set regs->ax = -ENOSYS and return -1L? I'll update the
git repository with that in any case.
Thanks!
#ifdef CONFIG_SECCOMP
/*
* Do seccomp after ptrace, to catch any tracer changes.
@@ -136,7 +146,7 @@ static long syscall_trace_enter(struct pt_regs *regs)
#define EXIT_TO_USERMODE_LOOP_FLAGS \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
- _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
+ _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_TASK_ISOLATION)
Where are you updating the conditions to force use of the slow path?
(That's _TIF_ALLWORK_MASK.)
Whenever _TIF_TASK_ISOLATION is set, _TIF_NOHZ is also set.
--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com
