static int bpf_core_patch_insn()

in third/libbpf/src/relo_core.c [919:1042]

• 108 lines of code
• 28 McCabe index (conditional complexity)

static int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
			       int insn_idx, const struct bpf_core_relo *relo,
			       int relo_idx, const struct bpf_core_relo_res *res)
{
	__u32 orig_val, new_val;
	__u8 class;

	class = BPF_CLASS(insn->code);

	if (res->poison) {
poison:
		/* poison second part of ldimm64 to avoid confusing error from
		 * verifier about "unknown opcode 00"
		 */
		if (is_ldimm64_insn(insn))
			bpf_core_poison_insn(prog_name, relo_idx, insn_idx + 1, insn + 1);
		bpf_core_poison_insn(prog_name, relo_idx, insn_idx, insn);
		return 0;
	}

	orig_val = res->orig_val;
	new_val = res->new_val;

	switch (class) {
	case BPF_ALU:
	case BPF_ALU64:
		if (BPF_SRC(insn->code) != BPF_K)
			return -EINVAL;
		if (res->validate && insn->imm != orig_val) {
			pr_warn("prog '%s': relo #%d: unexpected insn #%d (ALU/ALU64) value: got %u, exp %u -> %u\n",
				prog_name, relo_idx,
				insn_idx, insn->imm, orig_val, new_val);
			return -EINVAL;
		}
		orig_val = insn->imm;
		insn->imm = new_val;
		pr_debug("prog '%s': relo #%d: patched insn #%d (ALU/ALU64) imm %u -> %u\n",
			 prog_name, relo_idx, insn_idx,
			 orig_val, new_val);
		break;
	case BPF_LDX:
	case BPF_ST:
	case BPF_STX:
		if (res->validate && insn->off != orig_val) {
			pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDX/ST/STX) value: got %u, exp %u -> %u\n",
				prog_name, relo_idx, insn_idx, insn->off, orig_val, new_val);
			return -EINVAL;
		}
		if (new_val > SHRT_MAX) {
			pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) value too big: %u\n",
				prog_name, relo_idx, insn_idx, new_val);
			return -ERANGE;
		}
		if (res->fail_memsz_adjust) {
			pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) accesses field incorrectly. "
				"Make sure you are accessing pointers, unsigned integers, or fields of matching type and size.\n",
				prog_name, relo_idx, insn_idx);
			goto poison;
		}

		orig_val = insn->off;
		insn->off = new_val;
		pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) off %u -> %u\n",
			 prog_name, relo_idx, insn_idx, orig_val, new_val);

		if (res->new_sz != res->orig_sz) {
			int insn_bytes_sz, insn_bpf_sz;

			insn_bytes_sz = insn_bpf_size_to_bytes(insn);
			if (insn_bytes_sz != res->orig_sz) {
				pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) unexpected mem size: got %d, exp %u\n",
					prog_name, relo_idx, insn_idx, insn_bytes_sz, res->orig_sz);
				return -EINVAL;
			}

			insn_bpf_sz = insn_bytes_to_bpf_size(res->new_sz);
			if (insn_bpf_sz < 0) {
				pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) invalid new mem size: %u\n",
					prog_name, relo_idx, insn_idx, res->new_sz);
				return -EINVAL;
			}

			insn->code = BPF_MODE(insn->code) | insn_bpf_sz | BPF_CLASS(insn->code);
			pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) mem_sz %u -> %u\n",
				 prog_name, relo_idx, insn_idx, res->orig_sz, res->new_sz);
		}
		break;
	case BPF_LD: {
		__u64 imm;

		if (!is_ldimm64_insn(insn) ||
		    insn[0].src_reg != 0 || insn[0].off != 0 ||
		    insn[1].code != 0 || insn[1].dst_reg != 0 ||
		    insn[1].src_reg != 0 || insn[1].off != 0) {
			pr_warn("prog '%s': relo #%d: insn #%d (LDIMM64) has unexpected form\n",
				prog_name, relo_idx, insn_idx);
			return -EINVAL;
		}

		imm = insn[0].imm + ((__u64)insn[1].imm << 32);
		if (res->validate && imm != orig_val) {
			pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %u -> %u\n",
				prog_name, relo_idx,
				insn_idx, (unsigned long long)imm,
				orig_val, new_val);
			return -EINVAL;
		}

		insn[0].imm = new_val;
		insn[1].imm = 0; /* currently only 32-bit values are supported */
		pr_debug("prog '%s': relo #%d: patched insn #%d (LDIMM64) imm64 %llu -> %u\n",
			 prog_name, relo_idx, insn_idx,
			 (unsigned long long)imm, new_val);
		break;
	}
	default:
		pr_warn("prog '%s': relo #%d: trying to relocate unrecognized insn #%d, code:0x%x, src:0x%x, dst:0x%x, off:0x%x, imm:0x%x\n",
			prog_name, relo_idx, insn_idx, insn->code,
			insn->src_reg, insn->dst_reg, insn->off, insn->imm);
		return -EINVAL;
	}

	return 0;
}