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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id x15-20020a1709065acf00b0099bcf9c2ec6sm6059183ejs.75.2023.10.30.07.28.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Oct 2023 07:28:21 -0700 (PDT) Message-ID: <0ee068765d5992f4907a6d3320d4c7c5b9e6e4ba.camel@gmail.com> Subject: Re: [RFC bpf 1/2] bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END From: Eduard Zingerman To: Shung-Hsi Yu , bpf@vger.kernel.org Cc: Daniel Borkmann , Andrii Nakryiko , Alexei Starovoitov , Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , stable@vger.kernel.org, Mohamed Mahmoud , Tao Lyu Date: Mon, 30 Oct 2023 16:28:19 +0200 In-Reply-To: <20231030132145.20867-2-shung-hsi.yu@suse.com> References: <20231030132145.20867-1-shung-hsi.yu@suse.com> <20231030132145.20867-2-shung-hsi.yu@suse.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 3.50.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2023-10-30 at 21:21 +0800, Shung-Hsi Yu wrote: > BPF_END and BPF_NEG has a different specification for the source bit in > the opcode compared to other ALU/ALU64 instructions, and is either > reserved or use to specify the byte swap endianness. In both cases the > source bit does not encode source operand location, and src_reg is a > reserved field. >=20 > backtrack_insn() currently does not differentiate BPF_END and BPF_NEG > from other ALU/ALU64 instructions, which leads to r0 being incorrectly > marked as precise when processing BPF_ALU | BPF_TO_BE | BPF_END > instructions. This commit teaches backtrack_insn() to correctly mark > precision for such case. >=20 > While precise tracking of BPF_NEG and other BPF_END instructions are > correct and does not need fixing because their source bit are unset and > thus treated as the BPF_K case, this commit opt to process all BPF_NEG > and BPF_END instructions within the same if-clause so it better aligns > with current convention used in the verifier (e.g. check_alu_op). >=20 > Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking") > Cc: stable@vger.kernel.org > Reported-by: Mohamed Mahmoud > Tested-by: Toke H=C3=B8iland-J=C3=B8rgensen > Tested-by: Tao Lyu > Signed-off-by: Shung-Hsi Yu Acked-by: Eduard Zingerman > --- > kernel/bpf/verifier.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) >=20 > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 873ade146f3d..646dc49263fd 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -3426,7 +3426,12 @@ static int backtrack_insn(struct bpf_verifier_env = *env, int idx, int subseq_idx, > if (class =3D=3D BPF_ALU || class =3D=3D BPF_ALU64) { > if (!bt_is_reg_set(bt, dreg)) > return 0; > - if (opcode =3D=3D BPF_MOV) { > + if (opcode =3D=3D BPF_END || opcode =3D=3D BPF_NEG) { > + /* sreg is reserved and unused > + * dreg still need precision before this insn > + */ > + return 0; > + } else if (opcode =3D=3D BPF_MOV) { > if (BPF_SRC(insn->code) =3D=3D BPF_X) { > /* dreg =3D sreg or dreg =3D (s8, s16, s32)sreg > * dreg needs precision after this insn