Messages in this thread | | | Subject | Re: [PATCH v14 06/14] arch/x86: enable task isolation functionality | From | Chris Metcalf <> | Date | Wed, 10 Aug 2016 15:40:13 -0400 |
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On 8/10/2016 3:17 PM, Andy Lutomirski wrote: > 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
Right, I see that now in entry_SYSCALL_64_after_swapgs. Good.
> 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()).
If you are in task isolation mode (and you haven't also requested NOSIG), then attempting a system call fails, and you get a signal delivered. You convinced me that failing the syscall was the thing to do back here:
https://lkml.kernel.org/r/CALCETrUrc_LJyLJLHefSDYagCrNqqzKuknr6uLgVXnPW8PmZKw@mail.gmail.com
>>>> #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.
That does seem reasonable; I'll make the change.
-- Chris Metcalf, Mellanox Technologies http://www.mellanox.com
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