On 05/09/2019 12:58 PM, Eric Dumazet wrote: > On Thu, May 9, 2019 at 3:52 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote: >> On Wed, May 8, 2019 at 9:47 PM Alexei Starovoitov >> <alexei.starovoitov@xxxxxxxxx> wrote: >>> On Wed, May 08, 2019 at 04:17:29PM -0700, Eric Dumazet wrote: >>>> On Wed, May 8, 2019 at 4:09 PM Alexei Starovoitov >>>> <alexei.starovoitov@xxxxxxxxx> wrote: >>>>> On Wed, May 08, 2019 at 02:21:52PM -0700, Eric Dumazet wrote: >>>>>> Hi Alexei and Daniel >>>>>> >>>>>> I have a question about seccomp. >>>>>> >>>>>> It seems that after this patch, seccomp no longer needs a helper >>>>>> (seccomp_bpf_load()) >>>>>> >>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bd4cf0ed331a275e9bf5a49e6d0fd55dffc551b8 >>>>>> >>>>>> Are we detecting that a particular JIT code needs to call at least one >>>>>> function from the kernel at all ? >>>>> >>>>> Currently we don't track such things and trying very hard to avoid >>>>> any special cases for classic vs extended. >>>>> >>>>>> If the filter contains self-contained code (no call, just inline >>>>>> code), then we could use any room in whole vmalloc space, >>>>>> not only from the modules (which is something like 2GB total on x86_64) >>>>> >>>>> I believe there was an effort to make bpf progs and other executable things >>>>> to be everywhere too, but I lost the track of it. >>>>> It's not that hard to tweak x64 jit to emit 64-bit calls to helpers >>>>> when delta between call insn and a helper is more than 32-bit that fits >>>>> into call insn. iirc there was even such patch floating around. >>>>> >>>>> but what motivated you question? do you see 2GB space being full?! >>>> >>>> A customer seems to hit the limit, with about 75,000 threads, >>>> each one having a seccomp filter with 6 pages (plus one guard page >>>> given by vmalloc) >>> >>> Since cbpf doesn't have "fd as a program" concept I suspect >>> the same program was loaded 75k times. What a waste of kernel memory. >>> And, no, we're not going to extend or fix cbpf for this. >>> cbpf is frozen. seccomp needs to start using ebpf. >>> It can have one program to secure all threads. >>> If necessary single program can be customized via bpf maps >>> for each thread. >> >> Yes, docker seems to have a very generic implementation and should >> probably be fixed >> ( https://github.com/moby/moby/blob/v17.03.2-ce/profiles/seccomp/seccomp.go ) > > Even if the seccomp program was optimized to a few bytes, it would > still consume at least 2 pages in module vmalloc space, > so the limit in number of concurrent programs would be around 262,144 > > We might ask seccomp guys to detect that the same program is used, by > maintaining a hash of already loaded ones. > ( I see struct seccomp_filter has a @usage refcount_t ) +1, that would indeed be worth to pursue as a short term solution.
