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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id ov8-20020a170906fc0800b009b947f81c4asm1149630ejb.155.2023.10.31.08.38.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Oct 2023 08:38:30 -0700 (PDT) Message-ID: <8a9da941cc2aefba27da706e4e9b2d11aedfc86f.camel@gmail.com> Subject: Re: [PATCH v5 bpf-next 14/23] bpf: generalize is_branch_taken to handle all conditional jumps in one place From: Eduard Zingerman To: Andrii Nakryiko , bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org Cc: kernel-team@meta.com Date: Tue, 31 Oct 2023 17:38:29 +0200 In-Reply-To: <20231027181346.4019398-15-andrii@kernel.org> References: <20231027181346.4019398-1-andrii@kernel.org> <20231027181346.4019398-15-andrii@kernel.org> 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 Fri, 2023-10-27 at 11:13 -0700, Andrii Nakryiko wrote: > > Make is_branch_taken() a single entry point for branch pruning decision > > making, handling both pointer vs pointer, pointer vs scalar, and scalar > > vs scalar cases in one place. This also nicely cleans up check_cond_jmp= _op(). > >=20 > > Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman > > --- > > kernel/bpf/verifier.c | 49 ++++++++++++++++++++++--------------------- > > 1 file changed, 25 insertions(+), 24 deletions(-) > >=20 > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 25b5234ebda3..fedd6d0e76e5 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -14169,6 +14169,19 @@ static void find_good_pkt_pointers(struct bpf_= verifier_state *vstate, > > })); > > } > > =20 > > +/* check if register is a constant scalar value */ > > +static bool is_reg_const(struct bpf_reg_state *reg, bool subreg32) > > +{ > > + return reg->type =3D=3D SCALAR_VALUE && > > + tnum_is_const(subreg32 ? tnum_subreg(reg->var_off) : reg->var_= off); > > +} > > + > > +/* assuming is_reg_const() is true, return constant value of a registe= r */ > > +static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32) > > +{ > > + return subreg32 ? tnum_subreg(reg->var_off).value : reg->var_off.valu= e; > > +} > > + > > /* > > * , currently assuming reg2 is a constant > > */ > > @@ -14410,12 +14423,20 @@ static int is_pkt_ptr_branch_taken(struct bpf= _reg_state *dst_reg, > > static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_= state *reg2, > > u8 opcode, bool is_jmp32) > > { > > - struct tnum reg2_tnum =3D is_jmp32 ? tnum_subreg(reg2->var_off) : reg= 2->var_off; > > u64 val; > > =20 > > - if (!tnum_is_const(reg2_tnum)) > > + if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && != is_jmp32) > > + return is_pkt_ptr_branch_taken(reg1, reg2, opcode); > > + > > + /* try to make sure reg2 is a constant SCALAR_VALUE */ > > + if (!is_reg_const(reg2, is_jmp32)) { > > + opcode =3D flip_opcode(opcode); > > + swap(reg1, reg2); > > + } > > + /* for now we expect reg2 to be a constant to make any useful decisio= ns */ > > + if (!is_reg_const(reg2, is_jmp32)) > > return -1; > > - val =3D reg2_tnum.value; > > + val =3D reg_const_value(reg2, is_jmp32); > > =20 > > if (__is_pointer_value(false, reg1)) { > > if (!reg_not_null(reg1)) > > @@ -14896,27 +14917,7 @@ static int check_cond_jmp_op(struct bpf_verifi= er_env *env, > > } > > =20 > > is_jmp32 =3D BPF_CLASS(insn->code) =3D=3D BPF_JMP32; > > - > > - if (BPF_SRC(insn->code) =3D=3D BPF_K) { > > - pred =3D is_branch_taken(dst_reg, src_reg, opcode, is_jmp32); > > - } else if (src_reg->type =3D=3D SCALAR_VALUE && > > - is_jmp32 && tnum_is_const(tnum_subreg(src_reg->var_off))) { > > - pred =3D is_branch_taken(dst_reg, src_reg, opcode, is_jmp32); > > - } else if (src_reg->type =3D=3D SCALAR_VALUE && > > - !is_jmp32 && tnum_is_const(src_reg->var_off)) { > > - pred =3D is_branch_taken(dst_reg, src_reg, opcode, is_jmp32); > > - } else if (dst_reg->type =3D=3D SCALAR_VALUE && > > - is_jmp32 && tnum_is_const(tnum_subreg(dst_reg->var_off))) { > > - pred =3D is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_j= mp32); > > - } else if (dst_reg->type =3D=3D SCALAR_VALUE && > > - !is_jmp32 && tnum_is_const(dst_reg->var_off)) { > > - pred =3D is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_j= mp32); > > - } else if (reg_is_pkt_pointer_any(dst_reg) && > > - reg_is_pkt_pointer_any(src_reg) && > > - !is_jmp32) { > > - pred =3D is_pkt_ptr_branch_taken(dst_reg, src_reg, opcode); > > - } > > - > > + pred =3D is_branch_taken(dst_reg, src_reg, opcode, is_jmp32); > > if (pred >=3D 0) { > > /* If we get here with a dst_reg pointer type it is because > > * above is_branch_taken() special cased the 0 comparison.