Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 10 Aug 2016 12:17:54 -0700 | Subject | Re: [PATCH v14 06/14] arch/x86: enable task isolation functionality |
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On Aug 10, 2016 5:30 PM, "Chris Metcalf" <cmetcalf@mellanox.com> wrote: > > On 8/10/2016 3:52 AM, Andy Lutomirski wrote: >> >> On Aug 9, 2016 11:30 PM, "Chris Metcalf" <cmetcalf@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.
regs->ax will already be -ENOSYS unless something changed it, but I'm not sure what this code is trying to do. Is the idea that task_isolation_syscall might enqueue a signal and you want to deliver it without processing the syscall? If so, a comment would be nice. You could even WARN_ON(!signal_pending()).
> > 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.
OK, but why not decouple it a bit and add it to the mask? I keep meaning to add a BUILD_BUG_ON checking for bits in EXIT_TO_USERMODE_LOOP_FLAGS that aren't in the appropriate slow path masks.
> > -- > Chris Metcalf, Mellanox Technologies > http://www.mellanox.com >
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