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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id cm7-20020a170907938700b009ddf38056f8sm16965ejc.118.2023.11.03.09.47.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Nov 2023 09:47:31 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next 02/13] bpf: generalize is_scalar_branch_taken() logic 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: Fri, 03 Nov 2023 18:47:29 +0200 In-Reply-To: <20231103000822.2509815-3-andrii@kernel.org> References: <20231103000822.2509815-1-andrii@kernel.org> <20231103000822.2509815-3-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 Thu, 2023-11-02 at 17:08 -0700, Andrii Nakryiko wrote: > Generalize is_branch_taken logic for SCALAR_VALUE register to handle > cases when both registers are not constants. Previously supported > vs cases are a natural subset of more generic > vs set of cases. >=20 > Generalized logic relies on straightforward segment intersection checks. >=20 > Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman (With the same nitpick that '<' cases could be converted to '>' cases). > --- > kernel/bpf/verifier.c | 103 ++++++++++++++++++++++++++---------------- > 1 file changed, 63 insertions(+), 40 deletions(-) >=20 > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 52934080042c..2627461164ed 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -14187,82 +14187,104 @@ static int is_scalar_branch_taken(struct bpf_r= eg_state *reg1, struct bpf_reg_sta > u8 opcode, bool is_jmp32) > { > struct tnum t1 =3D is_jmp32 ? tnum_subreg(reg1->var_off) : reg1->var_of= f; > + struct tnum t2 =3D is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_of= f; > u64 umin1 =3D is_jmp32 ? (u64)reg1->u32_min_value : reg1->umin_value; > u64 umax1 =3D is_jmp32 ? (u64)reg1->u32_max_value : reg1->umax_value; > s64 smin1 =3D is_jmp32 ? (s64)reg1->s32_min_value : reg1->smin_value; > s64 smax1 =3D is_jmp32 ? (s64)reg1->s32_max_value : reg1->smax_value; > - u64 uval =3D is_jmp32 ? (u32)tnum_subreg(reg2->var_off).value : reg2->v= ar_off.value; > - s64 sval =3D is_jmp32 ? (s32)uval : (s64)uval; > + u64 umin2 =3D is_jmp32 ? (u64)reg2->u32_min_value : reg2->umin_value; > + u64 umax2 =3D is_jmp32 ? (u64)reg2->u32_max_value : reg2->umax_value; > + s64 smin2 =3D is_jmp32 ? (s64)reg2->s32_min_value : reg2->smin_value; > + s64 smax2 =3D is_jmp32 ? (s64)reg2->s32_max_value : reg2->smax_value; > =20 > switch (opcode) { > case BPF_JEQ: > - if (tnum_is_const(t1)) > - return !!tnum_equals_const(t1, uval); > - else if (uval < umin1 || uval > umax1) > + /* constants, umin/umax and smin/smax checks would be > + * redundant in this case because they all should match > + */ > + if (tnum_is_const(t1) && tnum_is_const(t2)) > + return t1.value =3D=3D t2.value; > + /* const ranges */ > + if (umin1 =3D=3D umax1 && umin2 =3D=3D umax2) > + return umin1 =3D=3D umin2; > + if (smin1 =3D=3D smax1 && smin2 =3D=3D smax2) > + return smin1 =3D=3D smin2; > + /* non-overlapping ranges */ > + if (umin1 > umax2 || umax1 < umin2) > return 0; > - else if (sval < smin1 || sval > smax1) > + if (smin1 > smax2 || smax1 < smin2) > return 0; > break; > case BPF_JNE: > - if (tnum_is_const(t1)) > - return !tnum_equals_const(t1, uval); > - else if (uval < umin1 || uval > umax1) > + /* constants, umin/umax and smin/smax checks would be > + * redundant in this case because they all should match > + */ > + if (tnum_is_const(t1) && tnum_is_const(t2)) > + return t1.value !=3D t2.value; > + /* non-overlapping ranges */ > + if (umin1 > umax2 || umax1 < umin2) > return 1; > - else if (sval < smin1 || sval > smax1) > + if (smin1 > smax2 || smax1 < smin2) > return 1; > break; > case BPF_JSET: > - if ((~t1.mask & t1.value) & uval) > + if (!is_reg_const(reg2, is_jmp32)) { > + swap(reg1, reg2); > + swap(t1, t2); > + } > + if (!is_reg_const(reg2, is_jmp32)) > + return -1; > + if ((~t1.mask & t1.value) & t2.value) > return 1; > - if (!((t1.mask | t1.value) & uval)) > + if (!((t1.mask | t1.value) & t2.value)) > return 0; > break; > case BPF_JGT: > - if (umin1 > uval ) > + if (umin1 > umax2) > return 1; > - else if (umax1 <=3D uval) > + else if (umax1 <=3D umin2) > return 0; > break; > case BPF_JSGT: > - if (smin1 > sval) > + if (smin1 > smax2) > return 1; > - else if (smax1 <=3D sval) > + else if (smax1 <=3D smin2) > return 0; > break; > case BPF_JLT: > - if (umax1 < uval) > + if (umax1 < umin2) > return 1; > - else if (umin1 >=3D uval) > + else if (umin1 >=3D umax2) > return 0; > break; > case BPF_JSLT: > - if (smax1 < sval) > + if (smax1 < smin2) > return 1; > - else if (smin1 >=3D sval) > + else if (smin1 >=3D smax2) > return 0; > break; > case BPF_JGE: > - if (umin1 >=3D uval) > + if (umin1 >=3D umax2) > return 1; > - else if (umax1 < uval) > + else if (umax1 < umin2) > return 0; > break; > case BPF_JSGE: > - if (smin1 >=3D sval) > + if (smin1 >=3D smax2) > return 1; > - else if (smax1 < sval) > + else if (smax1 < smin2) > return 0; > break; > case BPF_JLE: > - if (umax1 <=3D uval) > + if (umax1 <=3D umin2) > return 1; > - else if (umin1 > uval) > + else if (umin1 > umax2) > return 0; > break; > case BPF_JSLE: > - if (smax1 <=3D sval) > + if (smax1 <=3D smin2) > return 1; > - else if (smin1 > sval) > + else if (smin1 > smax2) > return 0; > break; > } > @@ -14341,28 +14363,28 @@ static int is_pkt_ptr_branch_taken(struct bpf_r= eg_state *dst_reg, > static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_st= ate *reg2, > u8 opcode, bool is_jmp32) > { > - u64 val; > - > if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is= _jmp32) > return is_pkt_ptr_branch_taken(reg1, reg2, opcode); > =20 > - /* 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 decisions= */ > - if (!is_reg_const(reg2, is_jmp32)) > - return -1; > - val =3D reg_const_value(reg2, is_jmp32); > + if (__is_pointer_value(false, reg1) || __is_pointer_value(false, reg2))= { > + u64 val; > + > + /* arrange that reg2 is a scalar, and reg1 is a pointer */ > + if (!is_reg_const(reg2, is_jmp32)) { > + opcode =3D flip_opcode(opcode); > + swap(reg1, reg2); > + } > + /* and ensure that reg2 is a constant */ > + if (!is_reg_const(reg2, is_jmp32)) > + return -1; > =20 > - if (__is_pointer_value(false, reg1)) { > if (!reg_not_null(reg1)) > return -1; > =20 > /* If pointer is valid tests against zero will fail so we can > * use this to direct branch taken. > */ > + val =3D reg_const_value(reg2, is_jmp32); > if (val !=3D 0) > return -1; > =20 > @@ -14376,6 +14398,7 @@ static int is_branch_taken(struct bpf_reg_state *= reg1, struct bpf_reg_state *reg > } > } > =20 > + /* now deal with two scalars, but not necessarily constants */ > return is_scalar_branch_taken(reg1, reg2, opcode, is_jmp32); > } > =20