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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id fw22-20020a170907501600b00a26b44ac54dsm10784083ejc.68.2024.01.02.11.24.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jan 2024 11:24:00 -0800 (PST) Message-ID: <85731a963139eb226b76069a5422ecbac063dd74.camel@gmail.com> Subject: Re: Funky verifier packet range error (> check works, != does not). From: Eduard Zingerman To: Maciej =?UTF-8?Q?=C5=BBenczykowski?= Cc: BPF Mailing List , Alexei Starovoitov Date: Tue, 02 Jan 2024 21:23:59 +0200 In-Reply-To: References: <1b75e54f235a7cb510768ca8142f15171024dd78.camel@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=mQGNBGKNNQEBDACwcUNXZOGTzn4rr7Sd18SA5Wv0Wna/ONE0ZwZEx+sIjyGrPOIhR14/DsOr3ZJer9UJ/WAJwbxOBj6E5Y2iF7grehljNbLr/jMjzPJ+hJpfOEAb5xjCB8xIqDoric1WRcCaRB+tDSk7jcsIIiMish0diTK3qTdu4MB6i/sh4aeFs2nifkNi3LdBuk8Xnk+RJHRoKFJ+C+EoSmQPuDQIRaF9N2m4yO0eG36N8jLwvUXnZzGvHkphoQ9ztbRJp58oh6xT7uH62m98OHbsVgzYKvHyBu/IU2ku5kVG9pLrFp25xfD4YdlMMkJH6l+jk+cpY0cvMTS1b6/g+1fyPM+uzD8Wy+9LtZ4PHwLZX+t4ONb/48i5AKq/jSsb5HWdciLuKEwlMyFAihZamZpEj+9n91NLPX4n7XeThXHaEvaeVVl4hfW/1Qsao7l1YjU/NCHuLaDeH4U1P59bagjwo9d1n5/PESeuD4QJFNqW+zkmE4tmyTZ6bPV6T5xdDRHeiITGc00AEQEAAbQkRWR1YXJkIFppbmdlcm1hbiA8ZWRkeXo4N0BnbWFpbC5jb20+iQHUBBMBCgA+FiEEx+6LrjApQyqnXCYELgxleklgRAkFAmKNNQECGwMFCQPCZwAFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AACgkQLgxleklgRAlWZAv/cJ5v3zlEyP0/jMKQBqbVCCHTirPEw+nqxbkeSO6r2FUds0NnGA9a6NPOpBH+qW7a6+n6q3sIbvH7jlss4pzLI7LYlDC6z+egTv7KR5X1xFrY1uR5UGs1beAjnzYeV2hK4yqRUfygsT0Wk5e4FiNBv4+DUZ8r0cNDkO6swJxU55DO21mcteC147+4aDoHZ40R0tsAu+brDGSSoOPpb0RWVsEf9XOBJqWWA+T7mluw nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.2 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-01-02 at 10:30 -0800, Maciej =C5=BBenczykowski wrote: [...] >=20 > The check is: > if (data + 98 !=3D data_end) return; > so now (after this check) you *know* that 'data + 98 =3D=3D data_end' and > thus you know there are *exactly* 98 valid bytes. Apologies, you are correct. So you want to have something along the following lines: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a376eb609c41..6ddb34d5b9aa 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14712,6 +14712,28 @@ static bool try_match_pkt_pointers(const struct bp= f_insn *insn, return false; } break; + case BPF_JEQ: + case BPF_JNE: + if ((dst_reg->type =3D=3D PTR_TO_PACKET && + src_reg->type =3D=3D PTR_TO_PACKET_END) || + (dst_reg->type =3D=3D PTR_TO_PACKET_META && + reg_is_init_pkt_pointer(src_reg, PTR_TO_PACKET)) || + (dst_reg->type =3D=3D PTR_TO_PACKET_END && + src_reg->type =3D=3D PTR_TO_PACKET) || + (reg_is_init_pkt_pointer(dst_reg, PTR_TO_PACKET) && + src_reg->type =3D=3D PTR_TO_PACKET_META)) { + /* pkt_data' !=3D pkt_end, pkt_meta' !=3D pkt_data, + * pkt_end !=3D pkt_data', pkt_data !=3D pkt_meta' + */ + struct bpf_verifier_state *eq_branch; + + eq_branch =3D BPF_OP(insn->code) =3D=3D BPF_JEQ ? o= ther_branch : this_branch; + find_good_pkt_pointers(eq_branch, dst_reg, dst_reg-= >type, true); + mark_pkt_end(eq_branch, insn->dst_reg, false); + } else { + return false; + } + break; case BPF_JGE: if ((dst_reg->type =3D=3D PTR_TO_PACKET && src_reg->type =3D=3D PTR_TO_PACKET_END) || Right? This passes the following test case: SEC("tc") __success __naked void data_plus_const_eq_pkt_end(void) { asm volatile (" \n\ r9 =3D r1; \n\ r1 =3D *(u32*)(r9 + %[__sk_buff_data]); \n\ r2 =3D *(u32*)(r9 + %[__sk_buff_data_end]); \n\ r3 =3D r1; \n\ r3 +=3D 8; \n\ if r3 !=3D r2 goto 1f; \n\ r1 =3D *(u64 *)(r1 + 0); \n\ 1: \n\ r0 =3D 0; \n\ exit; \n\ " : : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_e= nd)) : __clobber_all); } And it's variations for EQ/NEQ, positive/negative.