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Fri, 24 Oct 2025 09:21:14 -0700 (PDT) Message-ID: <0d98a2c754884e94c3367209680c071a8df4279d.camel@gmail.com> Subject: Re: [PATCH bpf-next 1/2] bpf: Skip bounds adjustment for conditional jumps on same register From: Eduard Zingerman To: KaFai Wan , Alexei Starovoitov Cc: Yonghong Song , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Song Liu , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Paul Chaignon , Matan Shachnai , Luis Gerhorst , colin.i.king@gmail.com, Harishankar Vishwanathan , bpf , LKML , "open list:KERNEL SELFTEST FRAMEWORK" , Kaiyan Mei , Yinhao Hu Date: Fri, 24 Oct 2025 09:21:11 -0700 In-Reply-To: References: <20251022164457.1203756-1-kafai.wan@linux.dev> <20251022164457.1203756-2-kafai.wan@linux.dev> <39af9321-fb9b-4cee-84f1-77248a375e85@linux.dev> <1d03174dfe2a7eab1166596c85a6b586a660dffc.camel@gmail.com> <0d267da41178f3ac4669621516888a06d6aa5665.camel@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-10-25 at 00:13 +0800, KaFai Wan wrote: [...] > For non-scalar cases we only allow pointer comparison on pkt_ptr, this ch= eck is before > is_branch_taken() >=20 > src_reg =3D ®s[insn->src_reg]; > if (!(reg_is_pkt_pointer_any(dst_reg) && reg_is_pkt_pointer_any(src_reg)= ) && > is_pointer_value(env, insn->src_reg)) { > verbose(env, "R%d pointer comparison prohibited\n", > insn->src_reg); > return -EACCES; > }=20 >=20 > and in the end of check_cond_jmp_op() (after is_branch_taken()), we check= ed again >=20 > } else if (!try_match_pkt_pointers(insn, dst_reg, ®s[insn->src_reg], > this_branch, other_branch) && > is_pointer_value(env, insn->dst_reg)) { > verbose(env, "R%d pointer comparison prohibited\n", > insn->dst_reg); > return -EACCES; > } >=20 > this time we=C2=A0check if it is valid comparison on pkt_ptr in try_match= _pkt_pointers().=C2=A0 >=20 > Currently we just allow 4 opcode (BPF_JGT, BPF_JLT, BPF_JGE, BPF_JLE) on = pkt_ptr, and with > conditions. But we bypass these prohibits in privileged mode (is_pointer_= value() always=C2=A0 > return false in privileged mode). >=20 > So the logic skip these prohibits for pkt_ptr in unprivileged mode. Well, yes, but do you really need to do forbid `if r0 > r0 goto ...` in unp= riv?