mirror of https://gitee.com/openkylin/linux.git
bpf: improve verifier branch analysis
pathological bpf programs may try to force verifier to explode in
the number of branch states:
20: (d5) if r1 s<= 0x24000028 goto pc+0
21: (b5) if r0 <= 0xe1fa20 goto pc+2
22: (d5) if r1 s<= 0x7e goto pc+0
23: (b5) if r0 <= 0xe880e000 goto pc+0
24: (c5) if r0 s< 0x2100ecf4 goto pc+0
25: (d5) if r1 s<= 0xe880e000 goto pc+1
26: (c5) if r0 s< 0xf4041810 goto pc+0
27: (d5) if r1 s<= 0x1e007e goto pc+0
28: (b5) if r0 <= 0xe86be000 goto pc+0
29: (07) r0 += 16614
30: (c5) if r0 s< 0x6d0020da goto pc+0
31: (35) if r0 >= 0x2100ecf4 goto pc+0
Teach verifier to recognize always taken and always not taken branches.
This analysis is already done for == and != comparison.
Expand it to all other branches.
It also helps real bpf programs to be verified faster:
before after
bpf_lb-DLB_L3.o 2003 1940
bpf_lb-DLB_L4.o 3173 3089
bpf_lb-DUNKNOWN.o 1080 1065
bpf_lxc-DDROP_ALL.o 29584 28052
bpf_lxc-DUNKNOWN.o 36916 35487
bpf_netdev.o 11188 10864
bpf_overlay.o 6679 6643
bpf_lcx_jit.o 39555 38437
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Alexei Starovoitov
Daniel Borkmann
parent
c3494801cd
commit
4f7b3e8258
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@ -3751,6 +3751,79 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
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}
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}
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/* compute branch direction of the expression "if (reg opcode val) goto target;"
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* and return:
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* 1 - branch will be taken and "goto target" will be executed
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* 0 - branch will not be taken and fall-through to next insn
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* -1 - unknown. Example: "if (reg < 5)" is unknown when register value range [0,10]
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*/
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static int is_branch_taken(struct bpf_reg_state *reg, u64 val, u8 opcode)
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{
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if (__is_pointer_value(false, reg))
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return -1;
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switch (opcode) {
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case BPF_JEQ:
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if (tnum_is_const(reg->var_off))
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return !!tnum_equals_const(reg->var_off, val);
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break;
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case BPF_JNE:
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if (tnum_is_const(reg->var_off))
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return !tnum_equals_const(reg->var_off, val);
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break;
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case BPF_JGT:
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if (reg->umin_value > val)
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return 1;
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else if (reg->umax_value <= val)
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return 0;
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break;
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case BPF_JSGT:
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if (reg->smin_value > (s64)val)
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return 1;
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else if (reg->smax_value < (s64)val)
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return 0;
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break;
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case BPF_JLT:
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if (reg->umax_value < val)
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return 1;
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else if (reg->umin_value >= val)
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return 0;
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break;
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case BPF_JSLT:
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if (reg->smax_value < (s64)val)
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return 1;
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else if (reg->smin_value >= (s64)val)
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return 0;
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break;
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case BPF_JGE:
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if (reg->umin_value >= val)
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return 1;
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else if (reg->umax_value < val)
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return 0;
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break;
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case BPF_JSGE:
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if (reg->smin_value >= (s64)val)
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return 1;
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else if (reg->smax_value < (s64)val)
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return 0;
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break;
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case BPF_JLE:
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if (reg->umax_value <= val)
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return 1;
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else if (reg->umin_value > val)
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return 0;
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break;
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case BPF_JSLE:
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if (reg->smax_value <= (s64)val)
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return 1;
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else if (reg->smin_value > (s64)val)
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return 0;
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break;
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}
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return -1;
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}
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/* Adjusts the register min/max values in the case that the dst_reg is the
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* variable register that we are working on, and src_reg is a constant or we're
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* simply doing a BPF_K check.
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@ -4152,21 +4225,15 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
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dst_reg = ®s[insn->dst_reg];
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/* detect if R == 0 where R was initialized to zero earlier */
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if (BPF_SRC(insn->code) == BPF_K &&
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(opcode == BPF_JEQ || opcode == BPF_JNE) &&
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dst_reg->type == SCALAR_VALUE &&
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tnum_is_const(dst_reg->var_off)) {
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if ((opcode == BPF_JEQ && dst_reg->var_off.value == insn->imm) ||
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(opcode == BPF_JNE && dst_reg->var_off.value != insn->imm)) {
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/* if (imm == imm) goto pc+off;
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* only follow the goto, ignore fall-through
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*/
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if (BPF_SRC(insn->code) == BPF_K) {
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int pred = is_branch_taken(dst_reg, insn->imm, opcode);
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if (pred == 1) {
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/* only follow the goto, ignore fall-through */
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*insn_idx += insn->off;
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return 0;
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} else {
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/* if (imm != imm) goto pc+off;
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* only follow fall-through branch, since
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} else if (pred == 0) {
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/* only follow fall-through branch, since
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* that's where the program will go
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*/
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return 0;
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@ -8576,7 +8576,7 @@ static struct bpf_test tests[] = {
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BPF_JMP_IMM(BPF_JA, 0, 0, -7),
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},
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.fixup_map_hash_8b = { 4 },
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.errstr = "R0 invalid mem access 'inv'",
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.errstr = "unbounded min value",
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.result = REJECT,
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},
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{
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@ -10547,7 +10547,7 @@ static struct bpf_test tests[] = {
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"check deducing bounds from const, 5",
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.insns = {
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BPF_MOV64_IMM(BPF_REG_0, 0),
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BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
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BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 1),
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BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
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BPF_EXIT_INSN(),
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},
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