On Wed, Aug 10, 2016 at 12:40 PM, Chris Metcalf <[email protected]> wrote: > On 8/10/2016 3:17 PM, Andy Lutomirski wrote: >> >> On Aug 10, 2016 5:30 PM, "Chris Metcalf" <[email protected]> wrote: >>> >>> On 8/10/2016 3:52 AM, Andy Lutomirski wrote: >>>> >>>> On Aug 9, 2016 11:30 PM, "Chris Metcalf" <[email protected]> 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_ljyljlhefsdyagcrnqqzkuknr6ulgvxnpw8pm...@mail.gmail.com
Indeed. Then please add the comment any maybe the WARN_ON. > >>>>> #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 > -- Andy Lutomirski AMA Capital Management, LLC
