static int bpf_jit_blind_insn()

in lcc/glcc/lib/ebpf/core.c [653:760]

• 98 lines of code
• 46 McCabe index (conditional complexity)

static int bpf_jit_blind_insn(const struct bpf_insn *from,
			      const struct bpf_insn *aux,
			      struct bpf_insn *to_buff)
{
	struct bpf_insn *to = to_buff;
	u32 imm_rnd = get_random_int();
	s16 off;

	BUILD_BUG_ON(BPF_REG_AX  + 1 != MAX_BPF_JIT_REG);
	BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG);

	if (from->imm == 0 &&
	    (from->code == (BPF_ALU   | BPF_MOV | BPF_K) ||
	     from->code == (BPF_ALU64 | BPF_MOV | BPF_K))) {
		*to++ = BPF_ALU64_REG(BPF_XOR, from->dst_reg, from->dst_reg);
		goto out;
	}

	switch (from->code) {
	case BPF_ALU | BPF_ADD | BPF_K:
	case BPF_ALU | BPF_SUB | BPF_K:
	case BPF_ALU | BPF_AND | BPF_K:
	case BPF_ALU | BPF_OR  | BPF_K:
	case BPF_ALU | BPF_XOR | BPF_K:
	case BPF_ALU | BPF_MUL | BPF_K:
	case BPF_ALU | BPF_MOV | BPF_K:
	case BPF_ALU | BPF_DIV | BPF_K:
	case BPF_ALU | BPF_MOD | BPF_K:
		*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX);
		break;

	case BPF_ALU64 | BPF_ADD | BPF_K:
	case BPF_ALU64 | BPF_SUB | BPF_K:
	case BPF_ALU64 | BPF_AND | BPF_K:
	case BPF_ALU64 | BPF_OR  | BPF_K:
	case BPF_ALU64 | BPF_XOR | BPF_K:
	case BPF_ALU64 | BPF_MUL | BPF_K:
	case BPF_ALU64 | BPF_MOV | BPF_K:
	case BPF_ALU64 | BPF_DIV | BPF_K:
	case BPF_ALU64 | BPF_MOD | BPF_K:
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_ALU64_REG(from->code, from->dst_reg, BPF_REG_AX);
		break;

	case BPF_JMP | BPF_JEQ  | BPF_K:
	case BPF_JMP | BPF_JNE  | BPF_K:
	case BPF_JMP | BPF_JGT  | BPF_K:
	case BPF_JMP | BPF_JLT  | BPF_K:
	case BPF_JMP | BPF_JGE  | BPF_K:
	case BPF_JMP | BPF_JLE  | BPF_K:
	case BPF_JMP | BPF_JSGT | BPF_K:
	case BPF_JMP | BPF_JSLT | BPF_K:
	case BPF_JMP | BPF_JSGE | BPF_K:
	case BPF_JMP | BPF_JSLE | BPF_K:
	case BPF_JMP | BPF_JSET | BPF_K:
		/* Accommodate for extra offset in case of a backjump. */
		off = from->off;
		if (off < 0)
			off -= 2;
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_JMP_REG(from->code, from->dst_reg, BPF_REG_AX, off);
		break;

	case BPF_LD | BPF_ABS | BPF_W:
	case BPF_LD | BPF_ABS | BPF_H:
	case BPF_LD | BPF_ABS | BPF_B:
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_LD_IND(from->code, BPF_REG_AX, 0);
		break;

	case BPF_LD | BPF_IND | BPF_W:
	case BPF_LD | BPF_IND | BPF_H:
	case BPF_LD | BPF_IND | BPF_B:
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_ALU32_REG(BPF_ADD, BPF_REG_AX, from->src_reg);
		*to++ = BPF_LD_IND(from->code, BPF_REG_AX, 0);
		break;

	case BPF_LD | BPF_IMM | BPF_DW:
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[1].imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_ALU64_IMM(BPF_LSH, BPF_REG_AX, 32);
		*to++ = BPF_ALU64_REG(BPF_MOV, aux[0].dst_reg, BPF_REG_AX);
		break;
	case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */
		*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm);
		*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_ALU64_REG(BPF_OR,  aux[0].dst_reg, BPF_REG_AX);
		break;

	case BPF_ST | BPF_MEM | BPF_DW:
	case BPF_ST | BPF_MEM | BPF_W:
	case BPF_ST | BPF_MEM | BPF_H:
	case BPF_ST | BPF_MEM | BPF_B:
		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
		*to++ = BPF_STX_MEM(from->code, from->dst_reg, BPF_REG_AX, from->off);
		break;
	}
out:
	return to - to_buff;
}