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bpf: btf: Check members of struct/union
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This patch checks a few things of struct's members:

1) It has a valid size (e.g. a "const void" is invalid)
2) A member's size (+ its member's offset) does not exceed
   the containing struct's size.
3) The member's offset satisfies the alignment requirement

The above can only be done after the needs_resolve member's type
is resolved.  Hence, the above is done together in
btf_struct_resolve().

Each possible member's type (e.g. int, enum, modifier...) implements
the check_member() ops which will be called from btf_struct_resolve().

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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Martin KaFai Lau authored and Daniel Borkmann committed Apr 19, 2018
1 parent eb3f595 commit 179cde8
Showing 1 changed file with 205 additions and 0 deletions.
205 changes: 205 additions & 0 deletions kernel/bpf/btf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -250,6 +250,10 @@ struct btf_kind_operations {
u32 meta_left);
int (*resolve)(struct btf_verifier_env *env,
const struct resolve_vertex *v);
int (*check_member)(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type);
void (*log_details)(struct btf_verifier_env *env,
const struct btf_type *t);
};
Expand Down Expand Up @@ -760,13 +764,61 @@ const struct btf_type *btf_type_id_size(const struct btf *btf,
return size_type;
}

static int btf_df_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
btf_verifier_log_basic(env, struct_type,
"Unsupported check_member");
return -EINVAL;
}

static int btf_df_resolve(struct btf_verifier_env *env,
const struct resolve_vertex *v)
{
btf_verifier_log_basic(env, v->t, "Unsupported resolve");
return -EINVAL;
}

static int btf_int_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
u32 int_data = btf_type_int(member_type);
u32 struct_bits_off = member->offset;
u32 struct_size = struct_type->size;
u32 nr_copy_bits;
u32 bytes_offset;

if (U32_MAX - struct_bits_off < BTF_INT_OFFSET(int_data)) {
btf_verifier_log_member(env, struct_type, member,
"bits_offset exceeds U32_MAX");
return -EINVAL;
}

struct_bits_off += BTF_INT_OFFSET(int_data);
bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);
nr_copy_bits = BTF_INT_BITS(int_data) +
BITS_PER_BYTE_MASKED(struct_bits_off);

if (nr_copy_bits > BITS_PER_U64) {
btf_verifier_log_member(env, struct_type, member,
"nr_copy_bits exceeds 64");
return -EINVAL;
}

if (struct_size < bytes_offset ||
struct_size - bytes_offset < BITS_ROUNDUP_BYTES(nr_copy_bits)) {
btf_verifier_log_member(env, struct_type, member,
"Member exceeds struct_size");
return -EINVAL;
}

return 0;
}

static s32 btf_int_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
Expand Down Expand Up @@ -830,9 +882,61 @@ static void btf_int_log(struct btf_verifier_env *env,
static const struct btf_kind_operations int_ops = {
.check_meta = btf_int_check_meta,
.resolve = btf_df_resolve,
.check_member = btf_int_check_member,
.log_details = btf_int_log,
};

static int btf_modifier_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
const struct btf_type *resolved_type;
u32 resolved_type_id = member->type;
struct btf_member resolved_member;
struct btf *btf = env->btf;

resolved_type = btf_type_id_size(btf, &resolved_type_id, NULL);
if (!resolved_type) {
btf_verifier_log_member(env, struct_type, member,
"Invalid member");
return -EINVAL;
}

resolved_member = *member;
resolved_member.type = resolved_type_id;

return btf_type_ops(resolved_type)->check_member(env, struct_type,
&resolved_member,
resolved_type);
}

static int btf_ptr_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
u32 struct_size, struct_bits_off, bytes_offset;

struct_size = struct_type->size;
struct_bits_off = member->offset;
bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);

if (BITS_PER_BYTE_MASKED(struct_bits_off)) {
btf_verifier_log_member(env, struct_type, member,
"Member is not byte aligned");
return -EINVAL;
}

if (struct_size - bytes_offset < sizeof(void *)) {
btf_verifier_log_member(env, struct_type, member,
"Member exceeds struct_size");
return -EINVAL;
}

return 0;
}

static int btf_ref_type_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
Expand Down Expand Up @@ -959,21 +1063,53 @@ static void btf_ref_type_log(struct btf_verifier_env *env,
static struct btf_kind_operations modifier_ops = {
.check_meta = btf_ref_type_check_meta,
.resolve = btf_modifier_resolve,
.check_member = btf_modifier_check_member,
.log_details = btf_ref_type_log,
};

static struct btf_kind_operations ptr_ops = {
.check_meta = btf_ref_type_check_meta,
.resolve = btf_ptr_resolve,
.check_member = btf_ptr_check_member,
.log_details = btf_ref_type_log,
};

static struct btf_kind_operations fwd_ops = {
.check_meta = btf_ref_type_check_meta,
.resolve = btf_df_resolve,
.check_member = btf_df_check_member,
.log_details = btf_ref_type_log,
};

static int btf_array_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
u32 struct_bits_off = member->offset;
u32 struct_size, bytes_offset;
u32 array_type_id, array_size;
struct btf *btf = env->btf;

if (BITS_PER_BYTE_MASKED(struct_bits_off)) {
btf_verifier_log_member(env, struct_type, member,
"Member is not byte aligned");
return -EINVAL;
}

array_type_id = member->type;
btf_type_id_size(btf, &array_type_id, &array_size);
struct_size = struct_type->size;
bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);
if (struct_size - bytes_offset < array_size) {
btf_verifier_log_member(env, struct_type, member,
"Member exceeds struct_size");
return -EINVAL;
}

return 0;
}

static s32 btf_array_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
Expand Down Expand Up @@ -1076,9 +1212,35 @@ static void btf_array_log(struct btf_verifier_env *env,
static struct btf_kind_operations array_ops = {
.check_meta = btf_array_check_meta,
.resolve = btf_array_resolve,
.check_member = btf_array_check_member,
.log_details = btf_array_log,
};

static int btf_struct_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
u32 struct_bits_off = member->offset;
u32 struct_size, bytes_offset;

if (BITS_PER_BYTE_MASKED(struct_bits_off)) {
btf_verifier_log_member(env, struct_type, member,
"Member is not byte aligned");
return -EINVAL;
}

struct_size = struct_type->size;
bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);
if (struct_size - bytes_offset < member_type->size) {
btf_verifier_log_member(env, struct_type, member,
"Member exceeds struct_size");
return -EINVAL;
}

return 0;
}

static s32 btf_struct_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
Expand Down Expand Up @@ -1137,13 +1299,15 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
const struct resolve_vertex *v)
{
const struct btf_member *member;
int err;
u16 i;

/* Before continue resolving the next_member,
* ensure the last member is indeed resolved to a
* type with size info.
*/
if (v->next_member) {
const struct btf_type *last_member_type;
const struct btf_member *last_member;
u16 last_member_type_id;

Expand All @@ -1152,6 +1316,14 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
if (WARN_ON_ONCE(!env_type_is_resolved(env,
last_member_type_id)))
return -EINVAL;

last_member_type = btf_type_by_id(env->btf,
last_member_type_id);
err = btf_type_ops(last_member_type)->check_member(env, v->t,
last_member,
last_member_type);
if (err)
return err;
}

for_each_member_from(i, v->next_member, v->t, member) {
Expand All @@ -1170,6 +1342,12 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
env_stack_set_next_member(env, i + 1);
return env_stack_push(env, member_type, member_type_id);
}

err = btf_type_ops(member_type)->check_member(env, v->t,
member,
member_type);
if (err)
return err;
}

env_stack_pop_resolved(env, 0, 0);
Expand All @@ -1186,9 +1364,35 @@ static void btf_struct_log(struct btf_verifier_env *env,
static struct btf_kind_operations struct_ops = {
.check_meta = btf_struct_check_meta,
.resolve = btf_struct_resolve,
.check_member = btf_struct_check_member,
.log_details = btf_struct_log,
};

static int btf_enum_check_member(struct btf_verifier_env *env,
const struct btf_type *struct_type,
const struct btf_member *member,
const struct btf_type *member_type)
{
u32 struct_bits_off = member->offset;
u32 struct_size, bytes_offset;

if (BITS_PER_BYTE_MASKED(struct_bits_off)) {
btf_verifier_log_member(env, struct_type, member,
"Member is not byte aligned");
return -EINVAL;
}

struct_size = struct_type->size;
bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);
if (struct_size - bytes_offset < sizeof(int)) {
btf_verifier_log_member(env, struct_type, member,
"Member exceeds struct_size");
return -EINVAL;
}

return 0;
}

static s32 btf_enum_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
Expand Down Expand Up @@ -1240,6 +1444,7 @@ static void btf_enum_log(struct btf_verifier_env *env,
static struct btf_kind_operations enum_ops = {
.check_meta = btf_enum_check_meta,
.resolve = btf_df_resolve,
.check_member = btf_enum_check_member,
.log_details = btf_enum_log,
};

Expand Down

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