bpf: Add btf enum64 support

Currently, BTF only supports upto 32bit enum value with BTF_KIND_ENUM.
But in kernel, some enum indeed has 64bit values, e.g.,
in uapi bpf.h, we have
  enum {
        BPF_F_INDEX_MASK                = 0xffffffffULL,
        BPF_F_CURRENT_CPU               = BPF_F_INDEX_MASK,
        BPF_F_CTXLEN_MASK               = (0xfffffULL << 32),
  };
In this case, BTF_KIND_ENUM will encode the value of BPF_F_CTXLEN_MASK
as 0, which certainly is incorrect.

This patch added a new btf kind, BTF_KIND_ENUM64, which permits
64bit value to cover the above use case. The BTF_KIND_ENUM64 has
the following three fields followed by the common type:
  struct bpf_enum64 {
    __u32 nume_off;
    __u32 val_lo32;
    __u32 val_hi32;
  };
Currently, btf type section has an alignment of 4 as all element types
are u32. Representing the value with __u64 will introduce a pad
for bpf_enum64 and may also introduce misalignment for the 64bit value.
Hence, two members of val_hi32 and val_lo32 are chosen to avoid these issues.

The kflag is also introduced for BTF_KIND_ENUM and BTF_KIND_ENUM64
to indicate whether the value is signed or unsigned. The kflag intends
to provide consistent output of BTF C fortmat with the original
source code. For example, the original BTF_KIND_ENUM bit value is 0xffffffff.
The format C has two choices, printing out 0xffffffff or -1 and current libbpf
prints out as unsigned value. But if the signedness is preserved in btf,
the value can be printed the same as the original source code.
The kflag value 0 means unsigned values, which is consistent to the default
by libbpf and should also cover most cases as well.

The new BTF_KIND_ENUM64 is intended to support the enum value represented as
64bit value. But it can represent all BTF_KIND_ENUM values as well.
The compiler ([1]) and pahole will generate BTF_KIND_ENUM64 only if the value has
to be represented with 64 bits.

In addition, a static inline function btf_kind_core_compat() is introduced which
will be used later when libbpf relo_core.c changed. Here the kernel shares the
same relo_core.c with libbpf.

  [1] https://reviews.llvm.org/D124641

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220607062600.3716578-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 129 insertions, 15 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 7bccaa4646e5..6c0d8480e15c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -309,6 +309,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_FLOAT]	= "FLOAT",
 	[BTF_KIND_DECL_TAG]	= "DECL_TAG",
 	[BTF_KIND_TYPE_TAG]	= "TYPE_TAG",
+	[BTF_KIND_ENUM64]	= "ENUM64",
 };
 
 const char *btf_type_str(const struct btf_type *t)
@@ -666,6 +667,7 @@ static bool btf_type_has_size(const struct btf_type *t)
 	case BTF_KIND_ENUM:
 	case BTF_KIND_DATASEC:
 	case BTF_KIND_FLOAT:
+	case BTF_KIND_ENUM64:
 		return true;
 	}
 
@@ -711,6 +713,11 @@ static const struct btf_decl_tag *btf_type_decl_tag(const struct btf_type *t)
 	return (const struct btf_decl_tag *)(t + 1);
 }
 
+static const struct btf_enum64 *btf_type_enum64(const struct btf_type *t)
+{
+	return (const struct btf_enum64 *)(t + 1);
+}
+
 static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
 {
 	return kind_ops[BTF_INFO_KIND(t->info)];
@@ -1019,6 +1026,7 @@ static const char *btf_show_name(struct btf_show *show)
 			parens = "{";
 		break;
 	case BTF_KIND_ENUM:
+	case BTF_KIND_ENUM64:
 		prefix = "enum";
 		break;
 	default:
@@ -1834,6 +1842,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		case BTF_KIND_UNION:
 		case BTF_KIND_ENUM:
 		case BTF_KIND_FLOAT:
+		case BTF_KIND_ENUM64:
 			size = type->size;
 			goto resolved;
 
@@ -3670,6 +3679,7 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 {
 	const struct btf_enum *enums = btf_type_enum(t);
 	struct btf *btf = env->btf;
+	const char *fmt_str;
 	u16 i, nr_enums;
 	u32 meta_needed;
 
@@ -3683,11 +3693,6 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 		return -EINVAL;
 	}
 
-	if (btf_type_kflag(t)) {
-		btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");
-		return -EINVAL;
-	}
-
 	if (t->size > 8 || !is_power_of_2(t->size)) {
 		btf_verifier_log_type(env, t, "Unexpected size");
 		return -EINVAL;
@@ -3718,7 +3723,8 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 
 		if (env->log.level == BPF_LOG_KERNEL)
 			continue;
-		btf_verifier_log(env, "\t%s val=%d\n",
+		fmt_str = btf_type_kflag(t) ? "\t%s val=%d\n" : "\t%s val=%u\n";
+		btf_verifier_log(env, fmt_str,
 				 __btf_name_by_offset(btf, enums[i].name_off),
 				 enums[i].val);
 	}
@@ -3759,7 +3765,10 @@ static void btf_enum_show(const struct btf *btf, const struct btf_type *t,
 		return;
 	}
 
-	btf_show_type_value(show, "%d", v);
+	if (btf_type_kflag(t))
+		btf_show_type_value(show, "%d", v);
+	else
+		btf_show_type_value(show, "%u", v);
 	btf_show_end_type(show);
 }
 
@@ -3772,6 +3781,109 @@ static struct btf_kind_operations enum_ops = {
 	.show = btf_enum_show,
 };
 
+static s32 btf_enum64_check_meta(struct btf_verifier_env *env,
+				 const struct btf_type *t,
+				 u32 meta_left)
+{
+	const struct btf_enum64 *enums = btf_type_enum64(t);
+	struct btf *btf = env->btf;
+	const char *fmt_str;
+	u16 i, nr_enums;
+	u32 meta_needed;
+
+	nr_enums = btf_type_vlen(t);
+	meta_needed = nr_enums * sizeof(*enums);
+
+	if (meta_left < meta_needed) {
+		btf_verifier_log_basic(env, t,
+				       "meta_left:%u meta_needed:%u",
+				       meta_left, meta_needed);
+		return -EINVAL;
+	}
+
+	if (t->size > 8 || !is_power_of_2(t->size)) {
+		btf_verifier_log_type(env, t, "Unexpected size");
+		return -EINVAL;
+	}
+
+	/* enum type either no name or a valid one */
+	if (t->name_off &&
+	    !btf_name_valid_identifier(env->btf, t->name_off)) {
+		btf_verifier_log_type(env, t, "Invalid name");
+		return -EINVAL;
+	}
+
+	btf_verifier_log_type(env, t, NULL);
+
+	for (i = 0; i < nr_enums; i++) {
+		if (!btf_name_offset_valid(btf, enums[i].name_off)) {
+			btf_verifier_log(env, "\tInvalid name_offset:%u",
+					 enums[i].name_off);
+			return -EINVAL;
+		}
+
+		/* enum member must have a valid name */
+		if (!enums[i].name_off ||
+		    !btf_name_valid_identifier(btf, enums[i].name_off)) {
+			btf_verifier_log_type(env, t, "Invalid name");
+			return -EINVAL;
+		}
+
+		if (env->log.level == BPF_LOG_KERNEL)
+			continue;
+
+		fmt_str = btf_type_kflag(t) ? "\t%s val=%lld\n" : "\t%s val=%llu\n";
+		btf_verifier_log(env, fmt_str,
+				 __btf_name_by_offset(btf, enums[i].name_off),
+				 btf_enum64_value(enums + i));
+	}
+
+	return meta_needed;
+}
+
+static void btf_enum64_show(const struct btf *btf, const struct btf_type *t,
+			    u32 type_id, void *data, u8 bits_offset,
+			    struct btf_show *show)
+{
+	const struct btf_enum64 *enums = btf_type_enum64(t);
+	u32 i, nr_enums = btf_type_vlen(t);
+	void *safe_data;
+	s64 v;
+
+	safe_data = btf_show_start_type(show, t, type_id, data);
+	if (!safe_data)
+		return;
+
+	v = *(u64 *)safe_data;
+
+	for (i = 0; i < nr_enums; i++) {
+		if (v != btf_enum64_value(enums + i))
+			continue;
+
+		btf_show_type_value(show, "%s",
+				    __btf_name_by_offset(btf,
+							 enums[i].name_off));
+
+		btf_show_end_type(show);
+		return;
+	}
+
+	if (btf_type_kflag(t))
+		btf_show_type_value(show, "%lld", v);
+	else
+		btf_show_type_value(show, "%llu", v);
+	btf_show_end_type(show);
+}
+
+static struct btf_kind_operations enum64_ops = {
+	.check_meta = btf_enum64_check_meta,
+	.resolve = btf_df_resolve,
+	.check_member = btf_enum_check_member,
+	.check_kflag_member = btf_enum_check_kflag_member,
+	.log_details = btf_enum_log,
+	.show = btf_enum64_show,
+};
+
 static s32 btf_func_proto_check_meta(struct btf_verifier_env *env,
 				     const struct btf_type *t,
 				     u32 meta_left)
@@ -4438,6 +4550,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
 	[BTF_KIND_FLOAT] = &float_ops,
 	[BTF_KIND_DECL_TAG] = &decl_tag_ops,
 	[BTF_KIND_TYPE_TAG] = &modifier_ops,
+	[BTF_KIND_ENUM64] = &enum64_ops,
 };
 
 static s32 btf_check_meta(struct btf_verifier_env *env,
@@ -5299,7 +5412,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 	/* skip modifiers */
 	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
-	if (btf_type_is_small_int(t) || btf_type_is_enum(t))
+	if (btf_type_is_small_int(t) || btf_is_any_enum(t))
 		/* accessing a scalar */
 		return true;
 	if (!btf_type_is_ptr(t)) {
@@ -5763,7 +5876,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
 	if (btf_type_is_ptr(t))
 		/* kernel size of pointer. Not BPF's size of pointer*/
 		return sizeof(void *);
-	if (btf_type_is_int(t) || btf_type_is_enum(t))
+	if (btf_type_is_int(t) || btf_is_any_enum(t))
 		return t->size;
 	*bad_type = t;
 	return -EINVAL;
@@ -5911,7 +6024,7 @@ static int btf_check_func_type_match(struct bpf_verifier_log *log,
 		 * to context only. And only global functions can be replaced.
 		 * Hence type check only those types.
 		 */
-		if (btf_type_is_int(t1) || btf_type_is_enum(t1))
+		if (btf_type_is_int(t1) || btf_is_any_enum(t1))
 			continue;
 		if (!btf_type_is_ptr(t1)) {
 			bpf_log(log,
@@ -6408,7 +6521,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
 	t = btf_type_by_id(btf, t->type);
 	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
-	if (!btf_type_is_int(t) && !btf_type_is_enum(t)) {
+	if (!btf_type_is_int(t) && !btf_is_any_enum(t)) {
 		bpf_log(log,
 			"Global function %s() doesn't return scalar. Only those are supported.\n",
 			tname);
@@ -6423,7 +6536,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
 		t = btf_type_by_id(btf, args[i].type);
 		while (btf_type_is_modifier(t))
 			t = btf_type_by_id(btf, t->type);
-		if (btf_type_is_int(t) || btf_type_is_enum(t)) {
+		if (btf_type_is_int(t) || btf_is_any_enum(t)) {
 			reg->type = SCALAR_VALUE;
 			continue;
 		}
@@ -7335,6 +7448,7 @@ recur:
 	case BTF_KIND_UNION:
 	case BTF_KIND_ENUM:
 	case BTF_KIND_FWD:
+	case BTF_KIND_ENUM64:
 		return 1;
 	case BTF_KIND_INT:
 		/* just reject deprecated bitfield-like integers; all other
@@ -7387,10 +7501,10 @@ recur:
  * field-based relocations. This function assumes that root types were already
  * checked for name match. Beyond that initial root-level name check, names
  * are completely ignored. Compatibility rules are as follows:
- *   - any two STRUCTs/UNIONs/FWDs/ENUMs/INTs are considered compatible, but
+ *   - any two STRUCTs/UNIONs/FWDs/ENUMs/INTs/ENUM64s are considered compatible, but
  *     kind should match for local and target types (i.e., STRUCT is not
  *     compatible with UNION);
- *   - for ENUMs, the size is ignored;
+ *   - for ENUMs/ENUM64s, the size is ignored;
  *   - for INT, size and signedness are ignored;
  *   - for ARRAY, dimensionality is ignored, element types are checked for
  *     compatibility recursively;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index aedac2ac02b9..2d2872682278 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10901,7 +10901,7 @@ static int check_btf_func(struct bpf_verifier_env *env,
 			goto err_free;
 		ret_type = btf_type_skip_modifiers(btf, func_proto->type, NULL);
 		scalar_return =
-			btf_type_is_small_int(ret_type) || btf_type_is_enum(ret_type);
+			btf_type_is_small_int(ret_type) || btf_is_any_enum(ret_type);
 		if (i && !scalar_return && env->subprog_info[i].has_ld_abs) {
 			verbose(env, "LD_ABS is only allowed in functions that return 'int'.\n");
 			goto err_free;