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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id cf13-20020a056512280d00b0050e7b274362sm505179lfb.99.2024.01.09.17.07.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jan 2024 17:07:57 -0800 (PST) Message-ID: <0055d2a9f2fdbbcb524252e103440c387d3b5f3d.camel@gmail.com> Subject: Re: [PATCH bpf-next 2/3] bpf: infer packet range for 'if pkt ==/!= pkt_end' comparisons From: Eduard Zingerman To: Yonghong Song , bpf@vger.kernel.org, ast@kernel.org Cc: andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, zenczykowski@gmail.com Date: Wed, 10 Jan 2024 03:07:56 +0200 In-Reply-To: References: <20240108132802.6103-1-eddyz87@gmail.com> <20240108132802.6103-3-eddyz87@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 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, 2024-01-09 at 09:26 -0800, Yonghong Song wrote: [...] >=20 > What will happen if there are multiple BPF_JEQ/BPF_JNE? I made a change t= o one of tests > in patch 3: >=20 > +SEC("tc") > +__success __log_level(2) > +__msg("if r3 !=3D r2 goto pc+3 ; R2_w=3Dpkt_end() R3_w=3Dpkt(off= =3D8,r=3D0xffffffffffffffff)") > +__naked void data_plus_const_neq_pkt_end(void) > +{ > + asm volatile (" \ > + r9 =3D r1; \ > + r1 =3D *(u32*)(r9 + %[__sk_buff_data]); \ > + r2 =3D *(u32*)(r9 + %[__sk_buff_data_end]); \ > + r3 =3D r1; \ > + r3 +=3D 8; \ > + if r3 !=3D r2 goto 1f; \ > + r3 +=3D 8; \ > + if r3 !=3D r2 goto 1f; \ > + r1 =3D *(u64 *)(r1 + 0); \ > +1: \ > + r0 =3D 0; \ > + exit; \ > +" : > + : __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), > + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data= _end)) > + : __clobber_all); > +} >=20 >=20 > The verifier output: > func#0 @0 > Global function data_plus_const_neq_pkt_end() doesn't return scalar. Only= those are supported. > 0: R1=3Dctx() R10=3Dfp0 > ; asm volatile (" \ > 0: (bf) r9 =3D r1 ; R1=3Dctx() R9_w=3Dctx() > 1: (61) r1 =3D *(u32 *)(r9 +76) ; R1_w=3Dpkt(r=3D0) R9_w=3Dctx() > 2: (61) r2 =3D *(u32 *)(r9 +80) ; R2_w=3Dpkt_end() R9_w=3Dctx() > 3: (bf) r3 =3D r1 ; R1_w=3Dpkt(r=3D0) R3_w=3Dpkt(r= =3D0) > 4: (07) r3 +=3D 8 ; R3_w=3Dpkt(off=3D8,r=3D0) > 5: (5d) if r3 !=3D r2 goto pc+3 ; R2_w=3Dpkt_end() R3_w=3Dpkt(off= =3D8,r=3D0xffffffffffffffff) > 6: (07) r3 +=3D 8 ; R3_w=3Dpkt(off=3D16,r=3D0xfffff= fffffffffff) > 7: (5d) if r3 !=3D r2 goto pc+1 ; R2_w=3Dpkt_end() R3_w=3Dpkt(off= =3D16,r=3D0xffffffffffffffff) > 8: (79) r1 =3D *(u64 *)(r1 +0) ; R1=3Dscalar() > 9: (b7) r0 =3D 0 ; R0_w=3D0 > 10: (95) exit >=20 > from 7 to 9: safe >=20 > from 5 to 9: safe > processed 13 insns (limit 1000000) max_states_per_insn 0 total_states 1 p= eak_states 1 mark_read 0 >=20 > insn 5, for this_branch (straight one), r3 range will be 8 and assuming p= kt_end is 8. > insn 7, r3 range becomes 18 and then we assume pkt_end is 16. >=20 > I guess we should handle this case. For branch 5 and 7, it cannot be that= both will be true. This is an interesting case. reg->range is set to AT_PKT_END or BEYOND_PKT_END only in try_match_pkt_pointers() (in mark_pkt_end() call). And this range mark appears not to be reset by +=3D operation (which might add a negative number as well). So, once r3 is marked AT_PKT_END it would remain so even after r3 +=3D 8, which is obviously not true. Not sure what to do yet.