On Tue, Apr 03, 2018 at 07:34:25PM -0700, Alexei Starovoitov wrote: > On Tue, Apr 3, 2018 at 9:26 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > > On Tue, Apr 3, 2018 at 8:41 AM, Alexei Starovoitov > > <alexei.starovoitov@xxxxxxxxx> wrote: > >> On Tue, Apr 03, 2018 at 08:11:07AM -0700, Andy Lutomirski wrote: > >>> > > >>> >> "bpf: Restrict kernel image access functions when the kernel is locked down": > >>> >> This patch just sucks in general. > >>> > > >>> > Yes - but that's what Alexei Starovoitov specified. bpf kind of sucks since > >>> > it gives you unrestricted access to the kernel. > >>> > >>> bpf, in certain contexts, gives you unrestricted access to *reading* > >>> kernel memory. bpf should, under no circumstances, let you write to > >>> the kernel unless you're using fault injection or similar. > >>> > >>> I'm surprised that Alexei acked this patch. If something like XDP or > >>> bpfilter starts becoming widely used, this patch will require a lot of > >>> reworking to avoid breaking standard distros. > >> > >> my understanding was that this lockdown set attemps to disallow _reads_ > >> of kernel memory from anything, so first version of patch was adding > >> run-time checks for bpf_probe_read() which is no-go > >> and without this helper the bpf for tracing is losing a lot of its power, > >> so the easiest is to disable it all. > > > > Fair enough. > > Actually looking at the patch again: > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit/?h=efi-lock-down&id=78bb0059c3b8304a8d124b55feebc780fb3e0500 > The bpf is totally disabled in this patch. > If the only thing that folks are paranoid about is reading > arbitrary kernel memory with bpf_probe_read() helper > then preferred patch would be to disable it during verification > when in lockdown mode Sorry for I didn't fully understand your idea... Do you mean that using bpf verifier to filter out bpf program that uses bpf_probe_read()? . > No run-time overhead and android folks will be happy > that lockdown doesn't break their work. > They converted out-of-tree networking accounting > module and corresponding user daemon to use bpf: > https://www.linuxplumbersconf.org/2017/ocw/system/presentations/4791/original/eBPF%20cgroup%20filters%20for%20data%20usage%20accounting%20on%20Android.pdf Thanks Joey Lee -- 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
