[RFC PATCH -mm 0/4] mm, security, bpf: Fine-grained control over memory policy adjustments with lsm bpf

[Michal Hocko]

On Wed 15-11-23 09:52:38, Yafang Shao wrote:
> On Wed, Nov 15, 2023 at 12:58 AM Casey Schaufler <casey at schaufler-ca.com> wrote:
> >
> > On 11/14/2023 3:59 AM, Yafang Shao wrote:
> > > On Tue, Nov 14, 2023 at 6:15 PM Michal Hocko <mhocko at suse.com> wrote:
> > >> On Mon 13-11-23 11:15:06, Yafang Shao wrote:
> > >>> On Mon, Nov 13, 2023 at 12:45 AM Casey Schaufler <casey at schaufler-ca.com> wrote:
> > >>>> On 11/11/2023 11:34 PM, Yafang Shao wrote:
> > >>>>> Background
> > >>>>> ==========
> > >>>>>
> > >>>>> In our containerized environment, we've identified unexpected OOM events
> > >>>>> where the OOM-killer terminates tasks despite having ample free memory.
> > >>>>> This anomaly is traced back to tasks within a container using mbind(2) to
> > >>>>> bind memory to a specific NUMA node. When the allocated memory on this node
> > >>>>> is exhausted, the OOM-killer, prioritizing tasks based on oom_score,
> > >>>>> indiscriminately kills tasks. This becomes more critical with guaranteed
> > >>>>> tasks (oom_score_adj: -998) aggravating the issue.
> > >>>> Is there some reason why you can't fix the callers of mbind(2)?
> > >>>> This looks like an user space configuration error rather than a
> > >>>> system security issue.
> > >>> It appears my initial description may have caused confusion. In this
> > >>> scenario, the caller is an unprivileged user lacking any capabilities.
> > >>> While a privileged user, such as root, experiencing this issue might
> > >>> indicate a user space configuration error, the concerning aspect is
> > >>> the potential for an unprivileged user to disrupt the system easily.
> > >>> If this is perceived as a misconfiguration, the question arises: What
> > >>> is the correct configuration to prevent an unprivileged user from
> > >>> utilizing mbind(2)?"
> > >> How is this any different than a non NUMA (mbind) situation?
> > > In a UMA system, each gigabyte of memory carries the same cost.
> > > Conversely, in a NUMA architecture, opting to confine processes within
> > > a specific NUMA node incurs additional costs. In the worst-case
> > > scenario, if all containers opt to bind their memory exclusively to
> > > specific nodes, it will result in significant memory wastage.
> >
> > That still sounds like you've misconfigured your containers such
> > that they expect to get more memory than is available, and that
> > they have more control over it than they really do.
> 
> And again: What configuration method is suitable to limit user control
> over memory policy adjustments, besides the heavyweight seccomp
> approach?

This really depends on the workloads. What is the reason mbind is used
in the first place? Is it acceptable to partition the system so that
there is a numa node reserved for NUMA aware workloads? If not, have you
considered (already proposed numa=off)?
-- 
Michal Hocko
SUSE Labs