bpf: Add BTF_KIND_FLOAT support

On the kernel side, introduce a new btf_kind_operations. It is
similar to that of BTF_KIND_INT, however, it does not need to
handle encodings and bit offsets. Do not implement printing, since
the kernel does not know how to format floating-point values.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210226202256.116518-7-iii@linux.ibm.com

kernel/bpf/btf.c

@@ -173,7 +173,7 @@
 #define BITS_ROUNDUP_BYTES(bits) \
 	(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
 
-#define BTF_INFO_MASK 0x8f00ffff
+#define BTF_INFO_MASK 0x9f00ffff
 #define BTF_INT_MASK 0x0fffffff
 #define BTF_TYPE_ID_VALID(type_id) ((type_id) <= BTF_MAX_TYPE)
 #define BTF_STR_OFFSET_VALID(name_off) ((name_off) <= BTF_MAX_NAME_OFFSET)
@@ -280,6 +280,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_FUNC_PROTO]	= "FUNC_PROTO",
 	[BTF_KIND_VAR]		= "VAR",
 	[BTF_KIND_DATASEC]	= "DATASEC",
+	[BTF_KIND_FLOAT]	= "FLOAT",
 };
 
 static const char *btf_type_str(const struct btf_type *t)
@@ -574,6 +575,7 @@ static bool btf_type_has_size(const struct btf_type *t)
 	case BTF_KIND_UNION:
 	case BTF_KIND_ENUM:
 	case BTF_KIND_DATASEC:
+	case BTF_KIND_FLOAT:
 		return true;
 	}
 
@@ -1704,6 +1706,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		case BTF_KIND_STRUCT:
 		case BTF_KIND_UNION:
 		case BTF_KIND_ENUM:
+		case BTF_KIND_FLOAT:
 			size = type->size;
 			goto resolved;
 
@@ -1849,7 +1852,7 @@ static int btf_df_check_kflag_member(struct btf_verifier_env *env,
 	return -EINVAL;
 }
 
-/* Used for ptr, array and struct/union type members.
+/* Used for ptr, array struct/union and float type members.
  * int, enum and modifier types have their specific callback functions.
  */
 static int btf_generic_check_kflag_member(struct btf_verifier_env *env,
@@ -3675,6 +3678,81 @@ static const struct btf_kind_operations datasec_ops = {
 	.show			= btf_datasec_show,
 };
 
+static s32 btf_float_check_meta(struct btf_verifier_env *env,
+				const struct btf_type *t,
+				u32 meta_left)
+{
+	if (btf_type_vlen(t)) {
+		btf_verifier_log_type(env, t, "vlen != 0");
+		return -EINVAL;
+	}
+
+	if (btf_type_kflag(t)) {
+		btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");
+		return -EINVAL;
+	}
+
+	if (t->size != 2 && t->size != 4 && t->size != 8 && t->size != 12 &&
+	    t->size != 16) {
+		btf_verifier_log_type(env, t, "Invalid type_size");
+		return -EINVAL;
+	}
+
+	btf_verifier_log_type(env, t, NULL);
+
+	return 0;
+}
+
+static int btf_float_check_member(struct btf_verifier_env *env,
+				  const struct btf_type *struct_type,
+				  const struct btf_member *member,
+				  const struct btf_type *member_type)
+{
+	u64 start_offset_bytes;
+	u64 end_offset_bytes;
+	u64 misalign_bits;
+	u64 align_bytes;
+	u64 align_bits;
+
+	/* Different architectures have different alignment requirements, so
+	 * here we check only for the reasonable minimum. This way we ensure
+	 * that types after CO-RE can pass the kernel BTF verifier.
+	 */
+	align_bytes = min_t(u64, sizeof(void *), member_type->size);
+	align_bits = align_bytes * BITS_PER_BYTE;
+	div64_u64_rem(member->offset, align_bits, &misalign_bits);
+	if (misalign_bits) {
+		btf_verifier_log_member(env, struct_type, member,
+					"Member is not properly aligned");
+		return -EINVAL;
+	}
+
+	start_offset_bytes = member->offset / BITS_PER_BYTE;
+	end_offset_bytes = start_offset_bytes + member_type->size;
+	if (end_offset_bytes > struct_type->size) {
+		btf_verifier_log_member(env, struct_type, member,
+					"Member exceeds struct_size");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void btf_float_log(struct btf_verifier_env *env,
+			  const struct btf_type *t)
+{
+	btf_verifier_log(env, "size=%u", t->size);
+}
+
+static const struct btf_kind_operations float_ops = {
+	.check_meta = btf_float_check_meta,
+	.resolve = btf_df_resolve,
+	.check_member = btf_float_check_member,
+	.check_kflag_member = btf_generic_check_kflag_member,
+	.log_details = btf_float_log,
+	.show = btf_df_show,
+};
+
 static int btf_func_proto_check(struct btf_verifier_env *env,
 				const struct btf_type *t)
 {
@@ -3808,6 +3886,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
 	[BTF_KIND_FUNC_PROTO] = &func_proto_ops,
 	[BTF_KIND_VAR] = &var_ops,
 	[BTF_KIND_DATASEC] = &datasec_ops,
+	[BTF_KIND_FLOAT] = &float_ops,
 };
 
 static s32 btf_check_meta(struct btf_verifier_env *env,