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Message-ID: <fbe4fe4ae4f6f9db0d32208c0de8440647b24f91.camel@gmail.com>
Subject: Re: [PATCH bpf-next v7 3/5] bpf: Inline calls to bpf_loop when
 callback is known
From:   Eduard Zingerman <eddyz87@gmail.com>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Kernel Team <kernel-team@fb.com>, Song Liu <song@kernel.org>,
        Joanne Koong <joannelkoong@gmail.com>
Date:   Mon, 20 Jun 2022 15:59:03 +0300
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> On Sun, 2022-06-19 at 16:37 -0700, Alexei Starovoitov wrote:
> On Sun, Jun 19, 2022 at 3:01 PM Eduard Zingerman <eddyz87@gmail.com> wrot=
e:
> >=20
> > /* Mark a register as having a completely unknown (scalar) value. */
> > static void __mark_reg_unknown(const struct bpf_verifier_env *env,
> >                                struct bpf_reg_state *reg)
> > {
> >         ...
> >         reg->precise =3D env->subprog_cnt > 1 || !env->bpf_capable;
>=20
> Ahh. Thanks for explaining.
> We probably need to fix this conservative logic.
> Can you repro the issue when you comment out above ?

If I replace the assignment above with `reg->precise =3D false` the
verifier does skip the second branch with BPF_REG_4 set to 1.

> Let's skip the test for now. Just add mark_chain_precision
> to loop logic, so we don't have to come back to it later
> when subprogs>1 is fixed.

Will provide the updated version tonight, thank you for the
suggestions.

Best regards,
Eduard.