On Mo, 01.06.20 08:32, Paul Moore (paul@xxxxxxxxxxxxxx) wrote: > In situations where the calling application creates multiple per-ABI > filters, the seccomp_merge(3) function can be used to merge the > filters into one. There are some limitations (same byte ordering, > filter attributes, etc.) but in general it should work without problem > when merging x86_64, x32, and x86. Hmm, so we currently only use seccomp_rule_add_exact() to build an individual filter and finally seccomp_load() to install it. Which tells us exactly what works and what does not. If we now would use seccomp_rule_add_exact() to build the filters, but then use seccomp_merge() to merge them all, and then only do a single seccomp_load(), will this give us the same info? i.e. will seccomp_merge() give us the same errors seccomp_load() currently gives us when something cannot work? > > If we wanted to optimize that in userspace, then libseccomp would have > > to be improved quite substantially to let us know exactly what works > > and what doesn't, and to have sane fallback both when building > > whitelists and blacklists. > > It has been quite a while since we last talked about systemd's use of > libseccomp, but the upcoming v2.5.0 release (no date set yet, but > think weeks not months) finally takes a first step towards defining > proper return values on error for the API, no more "negative values on > error". I'm sure there are other things, but I recall this as being > one of the bigger systemd wants. Yes, we care about error codes a lot. > As an aside, it is always going to be difficult to allow fine grained > control when you have a single libseccomp filter that includes > multiple ABIs; the different ABI oddities are just too great (see > comments above). If you need exacting control of the filter, or ABI > specific handling, then the recommended way is to create those filters > independently and merge them together before loading them into the > kernel or applying any common rules. Hmm, so not sure I got this. But are you saying that when using seccomp_merge() am I supposed to merge filters for different archs into one megafilter, or are you saying the opposite: am I supposed not to do that? I.e. in an ideal world, should we come to a situation where per service on x86-64 we will have exactly one filter installed, or should we come to a situation where we'll have exactly three installed, once for each ABI? Lennart -- Lennart Poettering, Berlin
