[PATCH 1/1] security: Propagate universal pointer data in bpf hooks

[Paul Moore]

On Wed, Feb 26, 2025 at 2:06 AM Song Liu <song at kernel.org> wrote:
> On Tue, Feb 25, 2025 at 4:31 PM Blaise Boscaccy
> <bboscaccy at linux.microsoft.com> wrote:
> >
> > Certain bpf syscall subcommands are available for usage from both
> > userspace and the kernel. LSM modules or eBPF gatekeeper programs may
> > need to take a different course of action depending on whether or not
> > a BPF syscall originated from the kernel or userspace.
> >
> > Additionally, some of the bpf_attr struct fields contain pointers to
> > arbitrary memory. Currently the functionality to determine whether or
> > not a pointer refers to kernel memory or userspace memory is exposed
> > to the bpf verifier, but that information is missing from various LSM
> > hooks.
> >
> > Here we augment the LSM hooks to provide this data, by simply passing
> > the corresponding universal pointer in any hook that contains already
> > contains a bpf_attr struct that corresponds to a subcommand that may
> > be called from the kernel.
>
> I think this information is useful for LSM hooks.

I've only looked at it quickly, but so far it seems reasonable.  I'm
going to take a closer look today.

> Question: Do we need a full bpfptr_t for these hooks, or just a boolean
> "is_kernel or not"?

I may be misunderstanding the patch, but what if we swapped the
existing 'union bpf_attr' parameter for a 'bpfptr_t' parameter?  That
would allow for both kernel and usermode pointers, complete with a
'is_kernel' flag; or am I missing something (likely)?

-- 
paul-moore.com