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([2604:3d08:9880:5900:ad05:9ec6:fc65:cf63]) by smtp.gmail.com with ESMTPSA id i2-20020a170902c94200b001e27c404922sm2038316pla.130.2024.04.18.15.37.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Apr 2024 15:37:06 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v2 1/5] bpf/verifier: refactor checks for range computation From: Eduard Zingerman To: Cupertino Miranda , bpf@vger.kernel.org Cc: Yonghong Song , Alexei Starovoitov , David Faust , Elena Zannoni Date: Thu, 18 Apr 2024 15:37:05 -0700 In-Reply-To: <20240417122341.331524-2-cupertino.miranda@oracle.com> References: <20240417122341.331524-1-cupertino.miranda@oracle.com> <20240417122341.331524-2-cupertino.miranda@oracle.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.44.4-0ubuntu2 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2024-04-17 at 13:23 +0100, Cupertino Miranda wrote: [...] > @@ -13406,53 +13490,19 @@ static int adjust_scalar_min_max_vals(struct bp= f_verifier_env *env, [...] > - if (!src_known && > - opcode !=3D BPF_ADD && opcode !=3D BPF_SUB && opcode !=3D BPF_AND) = { > + int is_safe =3D is_safe_to_compute_dst_reg_range(insn, src_reg); > + switch (is_safe) { > + case UNCOMPUTABLE_RANGE: > __mark_reg_unknown(env, dst_reg); > return 0; > + case UNDEFINED_BEHAVIOUR: > + mark_reg_unknown(env, regs, insn->dst_reg); > + return 0; > + default: > + break; > } Nit: I know that the division between __mark_reg_unknown() and mark_reg_unknown() was asked for directly, but tbh I don't think that it adds any value here, here is how mark_reg_unknown() is implemented: static void mark_reg_unknown(struct bpf_verifier_env *env, struct bpf_reg_state *regs, u32 regno) { if (WARN_ON(regno >=3D MAX_BPF_REG)) { ... mark all regs not init ... return; } __mark_reg_unknown(env, regs + regno); } The 'regno >=3D MAX_BPF_REG' does not apply here, because adjust_scalar_min_max_vals() is only called from the following stack: - check_alu_op - adjust_reg_min_max_vals - adjust_scalar_min_max_vals The check_alu_op() does check_reg_arg() which verifies that both src and dst register numbers are within bounds. I suggest to replace the enum with as boolean value. Miranda, Yonhong, what do you think? [...]