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Thu, 02 Jan 2025 18:53:59 -0800 (PST) Message-ID: <478322da282bbdae28027967ff47bfe2504559fe.camel@gmail.com> Subject: Re: [PATCH bpf-next v6 4/5] bpf: verifier: Support eliding map lookup nullness From: Eduard Zingerman To: Daniel Xu , andrii@kernel.org, ast@kernel.org, shuah@kernel.org, daniel@iogearbox.net Cc: john.fastabend@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Thu, 02 Jan 2025 18:53:54 -0800 In-Reply-To: <86213ea40c6e6a30bf8ba967da9b9c4c6d77fd0b.1734667691.git.dxu@dxuuu.xyz> References: <86213ea40c6e6a30bf8ba967da9b9c4c6d77fd0b.1734667691.git.dxu@dxuuu.xyz> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.1 (3.54.1-1.fc41) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2024-12-19 at 21:09 -0700, Daniel Xu wrote: lgtm, but please see a note below. [...] > +/* Returns constant key value if possible, else negative error */ > +static s64 get_constant_map_key(struct bpf_verifier_env *env, > + struct bpf_reg_state *key, > + u32 key_size) > +{ > + struct bpf_func_state *state =3D func(env, key); > + struct bpf_reg_state *reg; > + int slot, spi, off; > + int spill_size =3D 0; > + int zero_size =3D 0; > + int stack_off; > + int i, err; > + u8 *stype; > + > + if (!env->bpf_capable) > + return -EOPNOTSUPP; > + if (key->type !=3D PTR_TO_STACK) > + return -EOPNOTSUPP; > + if (!tnum_is_const(key->var_off)) > + return -EOPNOTSUPP; > + > + stack_off =3D key->off + key->var_off.value; > + slot =3D -stack_off - 1; > + spi =3D slot / BPF_REG_SIZE; > + off =3D slot % BPF_REG_SIZE; > + stype =3D state->stack[spi].slot_type; > + > + /* First handle precisely tracked STACK_ZERO */ > + for (i =3D off; i >=3D 0 && stype[i] =3D=3D STACK_ZERO; i--) > + zero_size++; > + if (zero_size >=3D key_size) > + return 0; > + > + /* Check that stack contains a scalar spill of expected size */ > + if (!is_spilled_scalar_reg(&state->stack[spi])) > + return -EOPNOTSUPP; > + for (i =3D off; i >=3D 0 && stype[i] =3D=3D STACK_SPILL; i--) > + spill_size++; > + if (spill_size !=3D key_size) > + return -EOPNOTSUPP; > + > + reg =3D &state->stack[spi].spilled_ptr; > + if (!tnum_is_const(reg->var_off)) > + /* Stack value not statically known */ > + return -EOPNOTSUPP; > + > + /* We are relying on a constant value. So mark as precise > + * to prevent pruning on it. > + */ > + bt_set_frame_slot(&env->bt, env->cur_state->curframe, spi); I think env->cur_state->curframe is not always correct here. It should be key->frameno, as key might point a few stack frames up. > + err =3D mark_chain_precision_batch(env); > + if (err < 0) > + return err; > + > + return reg->var_off.value; > +} > + > static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > struct bpf_call_arg_meta *meta, > const struct bpf_func_proto *fn, [...]