On Fri, Jan 10, 2020 at 04:27:58PM +0100, KP Singh wrote: > On 09-Jan 14:47, Stephen Smalley wrote: > > On 1/9/20 2:43 PM, KP Singh wrote: > > > On 10-Jan 06:07, James Morris wrote: > > > > On Thu, 9 Jan 2020, Stephen Smalley wrote: > > > > > > > > > On 1/9/20 1:11 PM, James Morris wrote: > > > > > > On Wed, 8 Jan 2020, Stephen Smalley wrote: > > > > > > > > > > > > > The cover letter subject line and the Kconfig help text refer to it as a > > > > > > > BPF-based "MAC and Audit policy". It has an enforce config option that > > > > > > > enables the bpf programs to deny access, providing access control. IIRC, > > > > > > > in > > > > > > > the earlier discussion threads, the BPF maintainers suggested that Smack > > > > > > > and > > > > > > > other LSMs could be entirely re-implemented via it in the future, and that > > > > > > > such an implementation would be more optimal. > > > > > > > > > > > > In this case, the eBPF code is similar to a kernel module, rather than a > > > > > > loadable policy file. It's a loadable mechanism, rather than a policy, in > > > > > > my view. > > > > > > > > > > I thought you frowned on dynamically loadable LSMs for both security and > > > > > correctness reasons? > > > > > > Based on the feedback from the lists we've updated the design for v2. > > > > > > In v2, LSM hook callbacks are allocated dynamically using BPF > > > trampolines, appended to a separate security_hook_heads and run > > > only after the statically allocated hooks. > > > > > > The security_hook_heads for all the other LSMs (SELinux, AppArmor etc) > > > still remains __lsm_ro_after_init and cannot be modified. We are still > > > working on v2 (not ready for review yet) but the general idea can be > > > seen here: > > > > > > https://github.com/sinkap/linux-krsi/blob/patch/v1/trampoline_prototype/security/bpf/lsm.c > > > > > > > > > > > Evaluating the security impact of this is the next step. My understanding > > > > is that eBPF via BTF is constrained to read only access to hook > > > > parameters, and that its behavior would be entirely restrictive. > > > > > > > > I'd like to understand the security impact more fully, though. Can the > > > > eBPF code make arbitrary writes to the kernel, or read anything other than > > > > the correctly bounded LSM hook parameters? > > > > > > > > > > As mentioned, the BPF verifier does not allow writes to BTF types. > > > > > > > > And a traditional security module would necessarily fall > > > > > under GPL; is the eBPF code required to be likewise? If not, KRSI is a > > > > > gateway for proprietary LSMs... > > > > > > > > Right, we do not want this to be a GPL bypass. > > > > > > This is not intended to be a GPL bypass and the BPF verifier checks > > > for license compatibility of the loaded program with GPL. > > > > IIUC, it checks that the program is GPL compatible if it uses a function > > marked GPL-only. But what specifically is marked GPL-only that is required > > for eBPF programs using KRSI? > > Good point! If no-one objects, I can add it to the BPF_PROG_TYPE_LSM > specific verification for the v2 of the patch-set which would require > all BPF-LSM programs to be GPL. I don't think it's a good idea to enforce license on the program. The kernel doesn't do it for modules. For years all of BPF tracing progs were GPL because they have to use GPL-ed helpers to do anything meaningful. So for KRSI just make sure that all helpers are GPL-ed as well.
