On Fri, Oct 9, 2020 at 7:15 PM YiFei Zhu <zhuyifei1999@xxxxxxxxx> wrote: > The overhead of running Seccomp filters has been part of some past > discussions [1][2][3]. Oftentimes, the filters have a large number > of instructions that check syscall numbers one by one and jump based > on that. Some users chain BPF filters which further enlarge the > overhead. A recent work [6] comprehensively measures the Seccomp > overhead and shows that the overhead is non-negligible and has a > non-trivial impact on application performance. > > We observed some common filters, such as docker's [4] or > systemd's [5], will make most decisions based only on the syscall > numbers, and as past discussions considered, a bitmap where each bit > represents a syscall makes most sense for these filters. > > The fast (common) path for seccomp should be that the filter permits > the syscall to pass through, and failing seccomp is expected to be > an exceptional case; it is not expected for userspace to call a > denylisted syscall over and over. > > When it can be concluded that an allow must occur for the given > architecture and syscall pair (this determination is introduced in > the next commit), seccomp will immediately allow the syscall, > bypassing further BPF execution. > > Each architecture number has its own bitmap. The architecture > number in seccomp_data is checked against the defined architecture > number constant before proceeding to test the bit against the > bitmap with the syscall number as the index of the bit in the > bitmap, and if the bit is set, seccomp returns allow. The bitmaps > are all clear in this patch and will be initialized in the next > commit. [...] > Co-developed-by: Dimitrios Skarlatos <dskarlat@xxxxxxxxxx> > Signed-off-by: Dimitrios Skarlatos <dskarlat@xxxxxxxxxx> > Signed-off-by: YiFei Zhu <yifeifz2@xxxxxxxxxxxx> Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
