Re: [PATCH bpf-next v2] bpf: Return -ENOTSUPP if calls are not allowed in non-JITed programs

[Daniel Borkmann]

On 1/8/24 11:05 AM, Jiri Olsa wrote:
> On Thu, Jan 04, 2024 at 09:08:17PM +0800, Tiezhu Yang wrote:
> > If CONFIG_BPF_JIT_ALWAYS_ON is not set and bpf_jit_enable is 0, there
> > exist 6 failed tests.
> >
> >    [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
> >    [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
> >    [root@linux bpf]# ./test_verifier | grep FAIL
> >    #106/p inline simple bpf_loop call FAIL
> >    #107/p don't inline bpf_loop call, flags non-zero FAIL
> >    #108/p don't inline bpf_loop call, callback non-constant FAIL
> >    #109/p bpf_loop_inline and a dead func FAIL
> >    #110/p bpf_loop_inline stack locations for loop vars FAIL
> >    #111/p inline bpf_loop call in a big program FAIL
> >    Summary: 768 PASSED, 15 SKIPPED, 6 FAILED
> >
> > The test log shows that callbacks are not allowed in non-JITed programs,
> > interpreter doesn't support them yet, thus these tests should be skipped
> > if jit is disabled, just return -ENOTSUPP instead of -EINVAL for pseudo
> > calls in fixup_call_args().
> >
> > With this patch:
> >
> >    [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
> >    [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
> >    [root@linux bpf]# ./test_verifier | grep FAIL
> >    Summary: 768 PASSED, 21 SKIPPED, 0 FAILED
> >
> > Additionally, as Eduard suggested, return -ENOTSUPP instead of -EINVAL
> > for the other three places where "non-JITed" is used in error messages
> > to keep consistent.
> >
> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > ---
> >
> > v2:
> >    -- rebase on the latest bpf-next tree.
> >    -- return -ENOTSUPP instead of -EINVAL for the other three places
> >       where "non-JITed" is used in error messages to keep consistent.
> >    -- update the patch subject and commit message.
> >
> >   kernel/bpf/verifier.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index d5f4ff1eb235..99558a5186b2 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -8908,7 +8908,7 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
> >   			goto error;
> >   		if (env->subprog_cnt > 1 && !allow_tail_call_in_subprogs(env)) {
> >   			verbose(env, "tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls\n");
> > -			return -EINVAL;
> > +			return -ENOTSUPP;
>
> FWIW I agree with John review earlier [1], also there's chance (however small)
> we could mess up with some app already checking on that

+1, the ship on this has sailed unfortunately. Tiezhu, it would be good if you could
update the selftest handling instead.

> jirka
>
> [1] https://lore.kernel.org/bpf/6594a4c15a677_11e86208cd@john.notmuch/