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 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. 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 -- 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
