Messages in this thread | | | From | Rodrigo Campos <> | Date | Mon, 2 May 2022 14:48:35 +0200 | Subject | Re: [PATCH v3 1/2] seccomp: Add wait_killable semantic to seccomp user notifier |
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On Fri, Apr 29, 2022 at 8:20 PM Kees Cook <keescook@chromium.org> wrote: > On Fri, Apr 29, 2022 at 05:14:37PM +0000, Sargun Dhillon wrote: > > On Fri, Apr 29, 2022 at 11:42:15AM +0200, Rodrigo Campos wrote: > > > On Fri, Apr 29, 2022 at 4:32 AM Sargun Dhillon <sargun@sargun.me> wrote: > > > > the concept is searchable. If the notifying process is signaled prior > > > > to the notification being received by the userspace agent, it will > > > > be handled as normal. > > > > > > Why is that? Why not always handle in the same way (if wait killable > > > is set, wait like that) > > > > > > > The goal is to avoid two things: > > 1. Unncessary work - Often times, we see workloads that implement techniques > > like hedging (Also known as request racing[1]). In fact, RFC3484 > > (destination address selection) gets implemented where the DNS library > > will connect to many backend addresses and whichever one comes back first > > "wins". > > 2. Side effects - We don't want a situation where a syscall is in progress > > that is non-trivial to rollback (mount), and from user space's perspective > > this syscall never completed. > > > > Blocking before the syscall even starts is excessive. When we looked at this > > we found that with runtimes like Golang, they can get into a bad situation > > if they have many (1000s) of threads that are in the middle of a syscall > > because all of them need to elide prior to GC. In this case the runtime > > prioritizes the liveness of GC vs. the syscalls. > > > > That being said, there may be some syscalls in a filter that need the suggested > > behaviour. I can imagine introducing a new flag > > (say SECCOMP_FILTER_FLAG_WAIT_KILLABLE) that applies to all states. > > Alternatively, in one implementation, I put the behaviour in the data > > field of the return from the BPF filter.
Makes sense, if we need to, we can implement that in the future too.
> I'd add something like the above to the commit log, just to have it > around.
Yes, please. It was not obvious to me.
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