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

Alexei Starovoitov [off-list ref] writes:

On Tue, Feb 25, 2025 at 11:06 PM Song Liu [off-list ref] wrote:

quoted

On Tue, Feb 25, 2025 at 4:31 PM Blaise Boscaccy
[off-list ref] wrote:

quoted

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.

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

+1
Just passing the bool should do.
Passing uattr is a footgun. Last thing we need is to open up TOCTOU concerns.

Sounds good to me, I'll rework it to use a bool instead.

-blaise