libbpf: Factor out symtab and relos sanity checks

Factor out logic for sanity checking SHT_SYMTAB and SHT_REL sections into
separate sections. They are already quite extensive and are suffering from too
deep indentation. Subsequent changes will extend SYMTAB sanity checking
further, so it's better to factor each into a separate function.

No functional changes are intended.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-8-andrii@kernel.org

tools/lib/bpf/linker.c

@@ -131,6 +131,8 @@ static int init_output_elf(struct bpf_linker *linker, const char *file);
 
 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, struct src_obj *obj);
 static int linker_sanity_check_elf(struct src_obj *obj);
+static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
+static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
 static int linker_sanity_check_btf(struct src_obj *obj);
 static int linker_sanity_check_btf_ext(struct src_obj *obj);
 static int linker_fixup_btf(struct src_obj *obj);
@@ -663,8 +665,8 @@ static bool is_pow_of_2(size_t x)
 
 static int linker_sanity_check_elf(struct src_obj *obj)
 {
-	struct src_sec *sec, *link_sec;
+	struct src_sec *sec;
-	int i, j, n;
+	int i, err;
 
 	if (!obj->symtab_sec_idx) {
 		pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
@@ -692,8 +694,43 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 			return -EINVAL;
 
 		switch (sec->shdr->sh_type) {
-		case SHT_SYMTAB: {
+		case SHT_SYMTAB:
+			err = linker_sanity_check_elf_symtab(obj, sec);
+			if (err)
+				return err;
+			break;
+		case SHT_STRTAB:
+			break;
+		case SHT_PROGBITS:
+			if (sec->shdr->sh_flags & SHF_EXECINSTR) {
+				if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
+					return -EINVAL;
+			}
+			break;
+		case SHT_NOBITS:
+			break;
+		case SHT_REL:
+			err = linker_sanity_check_elf_relos(obj, sec);
+			if (err)
+				return err;
+			break;
+		case SHT_LLVM_ADDRSIG:
+			break;
+		default:
+			pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
+				sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
+{
+	struct src_sec *link_sec;
 	Elf64_Sym *sym;
+	int i, n;
 
 	if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
 		return -EINVAL;
@@ -714,34 +751,29 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 
 	n = sec->shdr->sh_size / sec->shdr->sh_entsize;
 	sym = sec->data->d_buf;
-			for (j = 0; j < n; j++, sym++) {
+	for (i = 0; i < n; i++, sym++) {
 		if (sym->st_shndx
 		    && sym->st_shndx < SHN_LORESERVE
 		    && sym->st_shndx >= obj->sec_cnt) {
 			pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
-						j, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
+				i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
 			return -EINVAL;
 		}
 		if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
 			if (sym->st_value != 0)
 				return -EINVAL;
+			continue;
 		}
 	}
-			break;
+
-		}
+	return 0;
-		case SHT_STRTAB:
+}
-			break;
+
-		case SHT_PROGBITS:
+static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
-			if (sec->shdr->sh_flags & SHF_EXECINSTR) {
+{
-				if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
+	struct src_sec *link_sec, *sym_sec;
-					return -EINVAL;
-			}
-			break;
-		case SHT_NOBITS:
-			break;
-		case SHT_REL: {
 	Elf64_Rel *relo;
-			struct src_sec *sym_sec;
+	int i, n;
 
 	if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
 		return -EINVAL;
@@ -773,11 +805,10 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 
 	/* don't further validate relocations for ignored sections */
 	if (link_sec->skipped)
-				break;
+		return 0;
 
 	/* relocatable section is data or instructions */
-			if (link_sec->shdr->sh_type != SHT_PROGBITS
+	if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
-			    && link_sec->shdr->sh_type != SHT_NOBITS) {
 		pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
 			sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
 		return -EINVAL;
@@ -787,40 +818,30 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 	n = sec->shdr->sh_size / sec->shdr->sh_entsize;
 	relo = sec->data->d_buf;
 	sym_sec = &obj->secs[obj->symtab_sec_idx];
-			for (j = 0; j < n; j++, relo++) {
+	for (i = 0; i < n; i++, relo++) {
 		size_t sym_idx = ELF64_R_SYM(relo->r_info);
 		size_t sym_type = ELF64_R_TYPE(relo->r_info);
 
 		if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32) {
 			pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
-						j, sec->sec_idx, sym_type, obj->filename);
+				i, sec->sec_idx, sym_type, obj->filename);
 			return -EINVAL;
 		}
 
 		if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
 			pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
-						j, sec->sec_idx, sym_idx, obj->filename);
+				i, sec->sec_idx, sym_idx, obj->filename);
 			return -EINVAL;
 		}
 
 		if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
 			if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
 				pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
-							j, sec->sec_idx, sym_idx, obj->filename);
+					i, sec->sec_idx, sym_idx, obj->filename);
 				return -EINVAL;
 			}
 		}
 	}
-			break;
-		}
-		case SHT_LLVM_ADDRSIG:
-			break;
-		default:
-			pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
-				sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
-			return -EINVAL;
-		}
-	}
 
 	return 0;
 }