On Fri, Sep 11, 2015 at 06:03:59PM +0200, Daniel Borkmann wrote: > On 09/11/2015 04:44 PM, Tycho Andersen wrote: > >On Fri, Sep 11, 2015 at 03:02:36PM +0200, Daniel Borkmann wrote: > >>On 09/11/2015 02:20 AM, Tycho Andersen wrote: > >>>In the next patch, we're going to add a way to access the underlying > >>>filters via bpf fds. This means that we need to ref-count both the > >>>struct seccomp_filter objects and the struct bpf_prog objects separately, > >>>in case a process dies but a filter is still referred to by another > >>>process. > >>> > >>>Additionally, we mark classic converted seccomp filters as seccomp eBPF > >>>programs, since they are a subset of what is supported in seccomp eBPF. > >>> > >>>Signed-off-by: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx> > >>>CC: Kees Cook <keescook@xxxxxxxxxxxx> > >>>CC: Will Drewry <wad@xxxxxxxxxxxx> > >>>CC: Oleg Nesterov <oleg@xxxxxxxxxx> > >>>CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > >>>CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> > >>>CC: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx> > >>>CC: Alexei Starovoitov <ast@xxxxxxxxxx> > >>>CC: Daniel Borkmann <daniel@xxxxxxxxxxxxx> > >>>--- > >>> kernel/seccomp.c | 4 +++- > >>> 1 file changed, 3 insertions(+), 1 deletion(-) > >>> > >>>diff --git a/kernel/seccomp.c b/kernel/seccomp.c > >>>index 245df6b..afaeddf 100644 > >>>--- a/kernel/seccomp.c > >>>+++ b/kernel/seccomp.c > >>>@@ -378,6 +378,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) > >>> } > >>> > >>> atomic_set(&sfilter->usage, 1); > >>>+ atomic_set(&sfilter->prog->aux->refcnt, 1); > >>>+ sfilter->prog->type = BPF_PROG_TYPE_SECCOMP; > >> > >>So, if you do this, then this breaks the assumption of eBPF JITs > >>that, currently, all classic converted BPF programs always have a > >>prog->type of BPF_PROG_TYPE_UNSPEC (see: bpf_prog_was_classic()). > >> > >>Currently, JITs make use of this information to determine whether > >>A and X mappings for such programs should or should not be cleared > >>in the prologue (s390 currently). > >> > >>In the seccomp_prepare_filter() stage, we're already past that, so > >>it will not cause an issue, but we certainly would need to be very > >>careful in future, if bpf_prog_was_classic() is then used at a later > >>stage when we already have a generated bpf_prog somewhere, as then > >>this assumption will break. > > > >The only reason we need to do this is to allow BPF_DUMP_PROG to work, > >since we were restricting it to only allow dumping of seccomp > >programs, since those don't have maps. Instead, perhaps we could allow > >dumping of BPF_PROG_TYPE_SECCOMP and BPF_PROG_TYPE_UNSPEC? > > There are possibilities that BPF_PROG_TYPE_UNSPEC is calling helpers > already today, at least in networking case, not seccomp. So, since > you want to export [classic -> eBPF] only for seccomp, put fds on them > and dump these via bpf(2), you could allow that (with a big comment > stating why it's safe), but mid-term we really need to sanitize all > this stuff properly as this is needed for other types, too. Sorry, just to be clear, you're suggesting that the patch is ok modulo a comment describing the jit issues? Tycho -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
