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Tue, 20 Oct 2026 14:00:17 -0700 (PDT) Received: from localhost ([153.61.198.240]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ad813ee970sm909417a91.16.2026.10.20.14.00.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Oct 2026 14:00:16 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Tue, 20 Oct 2026 21:00:15 +0000 Message-Id: Cc: , , , , , , Subject: Re: [PATCH bpf-next 1/2] bpf: support 32-bit linear scalar evolution From: "Alexei Starovoitov" To: , , In-Reply-To: <77720df26bea4edfd16a92d307115ad152f9ab558df8848fd8e0d7cb31e9f5eb@mail.kernel.org> References: <20261020-scev-32bit-v1-1-838f34f9f0cd@gmail.com> <77720df26bea4edfd16a92d307115ad152f9ab558df8848fd8e0d7cb31e9f5eb@mail.kernel.org> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Tue, Oct 20, 2026 at 04:35 AM bot+bpf-ci@kernel.org wrote: >> + if (!scev_value_compatible(env, st, &initial_val, &bound_val)) >> + return false; > > For a pointer-vs-pointer JMP32 latch (allowed for privileged programs, since > check_cond_jmp_op() only rejects pointer comparisons when !allow_ptr_leaks), > can the computed max_header_count end up smaller than the real number of > iterations? bpf_widen_scev_regs() and bpf_clamp_scev_regs() then bound the > induction pointer's range with that count, and the memory access checks > inside the loop depend on it being a true upper bound. > > Would it make sense to return false here when latch->jmp32 is set and either > initial_val.ptr_reg or bound_val.ptr_reg is >= 0? zext32 latches cannot > involve pointers, because ALU32 on pointers is rejected. Yes. Seems like a real bug. r1 = map_value + 0, r2 = map_value + 56 l: r1 += 8; if w1 <= w2 goto l max_header_count is 8 and r1 is clamped to 0..56. If the low 32 bits of r2 are 0xfffffff8 then w1 wraps to 0 and the latch stays true, so r1 walks past the map value. pls fix in a followup.