Re: [PATCH 18/27] bpf: Restrict kernel image access functions when the kernel is locked down

[David Howells]

Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:

> > @@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
> >  {
> >  	int ret;
> >  
> > +	if (kernel_is_locked_down("BPF")) {
> > +		memset(dst, 0, size);
> > +		return -EPERM;
> > +	}
>
> That doesn't help the lockdown purpose.
> If you don't trust the root the only way to prevent bpf read
> memory is to disable the whole thing.
> Have a single check in sys_bpf() to disallow everything if kernel_is_locked_down()
> and don't add overhead to critical path like bpf_probe_read().

TBH, I've no idea how bpf does anything, so I can't say whether this is
better, overkill or insufficient.

David