bpf: btf: Remove unused bits from uapi/linux/btf.h

This patch does the followings:
1. Limit BTF_MAX_TYPES and BTF_MAX_NAME_OFFSET to 64k.  We can
   raise it later.

2. Remove the BTF_TYPE_PARENT and BTF_STR_TBL_ELF_ID.  They are
   currently encoded at the highest bit of a u32.
   It is because the current use case does not require supporting
   parent type (i.e type_id referring to a type in another BTF file).
   It also does not support referring to a string in ELF.

   The BTF_TYPE_PARENT and BTF_STR_TBL_ELF_ID checks are replaced
   by BTF_TYPE_ID_CHECK and BTF_STR_OFFSET_CHECK which are
   defined in btf.c instead of uapi/linux/btf.h.

3. Limit the BTF_INFO_KIND from 5 bits to 4 bits which is enough.
   There is unused bits headroom if we ever needed it later.

4. The root bit in BTF_INFO is also removed because it is not
   used in the current use case.

5. Remove BTF_INT_VARARGS since func type is not supported now.
   The BTF_INT_ENCODING is limited to 4 bits instead of 8 bits.

The above can be added back later because the verifier
ensures the unused bits are zeros.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index 4fa4797..0b5ddbe 100644 (file)
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -22,28 +22,19 @@ struct btf_header {
 };
 
 /* Max # of type identifier */
-#define BTF_MAX_TYPE   0x7fffffff
+#define BTF_MAX_TYPE   0x0000ffff
 /* Max offset into the string section */
-#define BTF_MAX_NAME_OFFSET    0x7fffffff
+#define BTF_MAX_NAME_OFFSET    0x0000ffff
 /* Max # of struct/union/enum members or func args */
 #define BTF_MAX_VLEN   0xffff
 
-/* The type id is referring to a parent BTF */
-#define BTF_TYPE_PARENT(id)    (((id) >> 31) & 0x1)
-#define BTF_TYPE_ID(id)                ((id) & BTF_MAX_TYPE)
-
-/* String is in the ELF string section */
-#define BTF_STR_TBL_ELF_ID(ref)        (((ref) >> 31) & 0x1)
-#define BTF_STR_OFFSET(ref)    ((ref) & BTF_MAX_NAME_OFFSET)
-
 struct btf_type {
        __u32 name_off;
        /* "info" bits arrangement
         * bits  0-15: vlen (e.g. # of struct's members)
         * bits 16-23: unused
-        * bits 24-28: kind (e.g. int, ptr, array...etc)
-        * bits 29-30: unused
-        * bits    31: root
+        * bits 24-27: kind (e.g. int, ptr, array...etc)
+        * bits 28-31: unused
         */
        __u32 info;
        /* "size" is used by INT, ENUM, STRUCT and UNION.
@@ -58,8 +49,7 @@ struct btf_type {
        };
 };
 
-#define BTF_INFO_KIND(info)    (((info) >> 24) & 0x1f)
-#define BTF_INFO_ISROOT(info)  (!!(((info) >> 24) & 0x80))
+#define BTF_INFO_KIND(info)    (((info) >> 24) & 0x0f)
 #define BTF_INFO_VLEN(info)    ((info) & 0xffff)
 
 #define BTF_KIND_UNKN          0       /* Unknown      */
@@ -84,15 +74,14 @@ struct btf_type {
 /* BTF_KIND_INT is followed by a u32 and the following
  * is the 32 bits arrangement:
  */
-#define BTF_INT_ENCODING(VAL)  (((VAL) & 0xff000000) >> 24)
+#define BTF_INT_ENCODING(VAL)  (((VAL) & 0x0f000000) >> 24)
 #define BTF_INT_OFFSET(VAL)    (((VAL  & 0x00ff0000)) >> 16)
 #define BTF_INT_BITS(VAL)      ((VAL)  & 0x0000ffff)
 
 /* Attributes stored in the BTF_INT_ENCODING */
-#define BTF_INT_SIGNED 0x1
-#define BTF_INT_CHAR   0x2
-#define BTF_INT_BOOL   0x4
-#define BTF_INT_VARARGS        0x8
+#define BTF_INT_SIGNED (1 << 0)
+#define BTF_INT_CHAR   (1 << 1)
+#define BTF_INT_BOOL   (1 << 2)
 
 /* BTF_KIND_ENUM is followed by multiple "struct btf_enum".
  * The exact number of btf_enum is stored in the vlen (of the

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index e388a65..9cbeabb 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -163,13 +163,16 @@
 #define BITS_ROUNDUP_BYTES(bits) \
        (BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
 
+#define BTF_INFO_MASK 0x0f00ffff
+#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)
+
 /* 16MB for 64k structs and each has 16 members and
  * a few MB spaces for the string section.
  * The hard limit is S32_MAX.
  */
 #define BTF_MAX_SIZE (16 * 1024 * 1024)
-/* 64k. We can raise it later. The hard limit is S32_MAX. */
-#define BTF_MAX_NR_TYPES 65535
 
 #define for_each_member(i, struct_type, member)                        \
        for (i = 0, member = btf_type_member(struct_type);      \
@@ -383,8 +386,6 @@ static const char *btf_int_encoding_str(u8 encoding)
                return "CHAR";
        else if (encoding == BTF_INT_BOOL)
                return "BOOL";
-       else if (encoding == BTF_INT_VARARGS)
-               return "VARARGS";
        else
                return "UNKN";
 }
@@ -421,16 +422,16 @@ static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
 
 static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
 {
-       return !BTF_STR_TBL_ELF_ID(offset) &&
-               BTF_STR_OFFSET(offset) < btf->hdr.str_len;
+       return BTF_STR_OFFSET_VALID(offset) &&
+               offset < btf->hdr.str_len;
 }
 
 static const char *btf_name_by_offset(const struct btf *btf, u32 offset)
 {
-       if (!BTF_STR_OFFSET(offset))
+       if (!offset)
                return "(anon)";
-       else if (BTF_STR_OFFSET(offset) < btf->hdr.str_len)
-               return &btf->strings[BTF_STR_OFFSET(offset)];
+       else if (offset < btf->hdr.str_len)
+               return &btf->strings[offset];
        else
                return "(invalid-name-offset)";
 }
@@ -598,13 +599,13 @@ static int btf_add_type(struct btf_verifier_env *env, struct btf_type *t)
                struct btf_type **new_types;
                u32 expand_by, new_size;
 
-               if (btf->types_size == BTF_MAX_NR_TYPES) {
+               if (btf->types_size == BTF_MAX_TYPE) {
                        btf_verifier_log(env, "Exceeded max num of types");
                        return -E2BIG;
                }
 
                expand_by = max_t(u32, btf->types_size >> 2, 16);
-               new_size = min_t(u32, BTF_MAX_NR_TYPES,
+               new_size = min_t(u32, BTF_MAX_TYPE,
                                 btf->types_size + expand_by);
 
                new_types = kvzalloc(new_size * sizeof(*new_types),
@@ -934,6 +935,12 @@ static s32 btf_int_check_meta(struct btf_verifier_env *env,
        }
 
        int_data = btf_type_int(t);
+       if (int_data & ~BTF_INT_MASK) {
+               btf_verifier_log_basic(env, t, "Invalid int_data:%x",
+                                      int_data);
+               return -EINVAL;
+       }
+
        nr_bits = BTF_INT_BITS(int_data) + BTF_INT_OFFSET(int_data);
 
        if (nr_bits > BITS_PER_U64) {
@@ -947,12 +954,17 @@ static s32 btf_int_check_meta(struct btf_verifier_env *env,
                return -EINVAL;
        }
 
+       /*
+        * Only one of the encoding bits is allowed and it
+        * should be sufficient for the pretty print purpose (i.e. decoding).
+        * Multiple bits can be allowed later if it is found
+        * to be insufficient.
+        */
        encoding = BTF_INT_ENCODING(int_data);
        if (encoding &&
            encoding != BTF_INT_SIGNED &&
            encoding != BTF_INT_CHAR &&
-           encoding != BTF_INT_BOOL &&
-           encoding != BTF_INT_VARARGS) {
+           encoding != BTF_INT_BOOL) {
                btf_verifier_log_type(env, t, "Unsupported encoding");
                return -ENOTSUPP;
        }
@@ -1126,7 +1138,7 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env,
                return -EINVAL;
        }
 
-       if (BTF_TYPE_PARENT(t->type)) {
+       if (!BTF_TYPE_ID_VALID(t->type)) {
                btf_verifier_log_type(env, t, "Invalid type_id");
                return -EINVAL;
        }
@@ -1333,12 +1345,12 @@ static s32 btf_array_check_meta(struct btf_verifier_env *env,
        /* Array elem type and index type cannot be in type void,
         * so !array->type and !array->index_type are not allowed.
         */
-       if (!array->type || BTF_TYPE_PARENT(array->type)) {
+       if (!array->type || !BTF_TYPE_ID_VALID(array->type)) {
                btf_verifier_log_type(env, t, "Invalid elem");
                return -EINVAL;
        }
 
-       if (!array->index_type || BTF_TYPE_PARENT(array->index_type)) {
+       if (!array->index_type || !BTF_TYPE_ID_VALID(array->index_type)) {
                btf_verifier_log_type(env, t, "Invalid index");
                return -EINVAL;
        }
@@ -1507,7 +1519,7 @@ static s32 btf_struct_check_meta(struct btf_verifier_env *env,
                }
 
                /* A member cannot be in type void */
-               if (!member->type || BTF_TYPE_PARENT(member->type)) {
+               if (!member->type || !BTF_TYPE_ID_VALID(member->type)) {
                        btf_verifier_log_member(env, t, member,
                                                "Invalid type_id");
                        return -EINVAL;
@@ -1760,6 +1772,12 @@ static s32 btf_check_meta(struct btf_verifier_env *env,
        }
        meta_left -= sizeof(*t);
 
+       if (t->info & ~BTF_INFO_MASK) {
+               btf_verifier_log(env, "[%u] Invalid btf_info:%x",
+                                env->log_type_id, t->info);
+               return -EINVAL;
+       }
+
        if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX ||
            BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
                btf_verifier_log(env, "[%u] Invalid kind:%u",