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. - KP > > If these issues can be resolved, this may be a "safe" way to support > loadable LSM applications. > > Again, I'd be interested in knowing how this is is handled in the > networking stack (keeping in mind that LSM is a much more invasive API, > and may not be directly comparable). > > -- > James Morris > <jmorris@xxxxxxxxx> >
