On 2/5/24 10:38 PM, thinker.li@xxxxxxxxx wrote:
From: Kui-Feng Lee <thinker.li@xxxxxxxxx>
Collect argument information from the type information of stub functions to
mark arguments of BPF struct_ops programs with PTR_MAYBE_NULL if they are
nullable. A nullable argument is annotated by suffixing "__nullable" at
the argument name of stub function.
For nullable arguments, this patch sets an arg_info to label their reg_type
with PTR_TO_BTF_ID | PTR_TRUSTED | PTR_MAYBE_NULL. This makes the verifier
to check programs and ensure that they properly check the pointer. The
programs should check if the pointer is null before accessing the pointed
memory.
The implementer of a struct_ops type should annotate the arguments that can
be null. The implementer should define a stub function (empty) as a
placeholder for each defined operator. The name of a stub function should
be in the pattern "<st_op_type>__<operator name>". For example, for
test_maybe_null of struct bpf_testmod_ops, it's stub function name should
be "bpf_testmod_ops__test_maybe_null". You mark an argument nullable by
suffixing the argument name with "__nullable" at the stub function.
Since we already has stub functions for kCFI, we just reuse these stub
functions with the naming convention mentioned earlier. These stub
functions with the naming convention is only required if there are nullable
arguments to annotate. For functions having not nullable arguments, stub
functions are not necessary for the purpose of this patch.
This patch will prepare a list of struct bpf_ctx_arg_aux, aka arg_info, for
each member field of a struct_ops type. "arg_info" will be assigned to
"prog->aux->ctx_arg_info" of BPF struct_ops programs in
check_struct_ops_btf_id() so that it can be used by btf_ctx_access() later
to set reg_type properly for the verifier.
Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
---
include/linux/bpf.h | 18 ++++
kernel/bpf/bpf_struct_ops.c | 185 ++++++++++++++++++++++++++++++++++--
kernel/bpf/btf.c | 40 ++++++++
kernel/bpf/verifier.c | 6 ++
4 files changed, 242 insertions(+), 7 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9a2ee9456989..29d9ec1c4fd9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1709,6 +1709,19 @@ struct bpf_struct_ops {
struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS];
};
+/* Every member of a struct_ops type has an instance even the member is not
+ * an operator (function pointer). The "arg_info" field will be assigned to
+ * prog->aux->arg_info of BPF struct_ops programs to provide the argument
+ * information required by the verifier to verify the program.
+ *
+ * btf_ctx_access() will lookup prog->aux->arg_info to find the
+ * corresponding entry for an given argument.
+ */
+struct bpf_struct_ops_member_arg_info {
nit. Shorten it to bpf_struct_ops_arg_info.
+ struct bpf_ctx_arg_aux *arg_info;
+ u32 arg_info_cnt;
+};
+
struct bpf_struct_ops_desc {
struct bpf_struct_ops *st_ops;
@@ -1716,6 +1729,9 @@ struct bpf_struct_ops_desc {
const struct btf_type *value_type;
u32 type_id;
u32 value_id;
+
+ /* Collection of argument information for each member */
+ struct bpf_struct_ops_member_arg_info *member_arg_info;
nit. Same here on the struct's field name. s/member_arg_info/arg_info(s)/.
};
enum bpf_struct_ops_state {
@@ -2500,6 +2516,8 @@ int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
int bpf_prog_test_run_nf(struct bpf_prog *prog,
const union bpf_attr *kattr,
union bpf_attr __user *uattr);
+int btf_ctx_arg_offset(struct btf *btf, const struct btf_type *func_proto,
+ u32 arg_no);
This should be in btf.h. Its implementation is also in btf.c in this patch.
bool btf_ctx_access(int off, int size, enum bpf_access_type type,
const struct bpf_prog *prog,
struct bpf_insn_access_aux *info);
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index f98f580de77a..0db7e12a9244 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -116,17 +116,162 @@ static bool is_valid_value_type(struct btf *btf, s32 value_id,
return true;
}
+#define MAYBE_NULL_SUFFIX "__nullable"
+#define MAX_STUB_NAME 128
+
+static bool match_nullable_suffix(const char *name)
+{
+ int suffix_len, len;
+
+ if (!name)
+ return false;
+
+ suffix_len = sizeof(MAYBE_NULL_SUFFIX) - 1;
+ len = strlen(name);
+ if (len <= suffix_len)
This function looks almost the same as __kfunc_param_match_suffix. How about
refactor __kfunc_param_match_suffix (to btf.c?) and resue here to avoid
duplicating code?
The only difference is between the "<=" here and the "<" there. I think the "<="
here may be a little better.
+ return false;
+
+ return !strcmp(name + len - suffix_len, MAYBE_NULL_SUFFIX);
+}
+
+/* Return the type info of a stub function, if it exists.
+ *
+ * The name of the stub function is made up of the name of the struct_ops
+ * and the name of the function pointer member, separated by "__". For
+ * example, if the struct_ops is named "foo_ops" and the function pointer
+ * member is named "bar", the stub function name would be "foo_ops__bar".
+ */
+static const struct btf_type *
I think there is double spaces.
+find_stub_func_proto(struct btf *btf, const char *st_op_name,
+ const char *member_name)
+{
+ char stub_func_name[MAX_STUB_NAME];
+ const struct btf_type *t, *func_proto;
+ s32 btf_id;
+
+ snprintf(stub_func_name, MAX_STUB_NAME, "%s__%s",
+ st_op_name, member_name);
check truncated case.
+ btf_id = btf_find_by_name_kind(btf, stub_func_name, BTF_KIND_FUNC);
+ if (btf_id < 0)
+ return NULL;
+ t = btf_type_by_id(btf, btf_id);
+ if (!t)
+ return NULL;
+ func_proto = btf_type_by_id(btf, t->type);
nit. directly "return btf_type_by_id(btf, t->type);"
+
+ return func_proto;
+}
+
+/* Prepare argument info for every nullable argument of a member of a
+ * struct_ops type.
+ *
+ * Initialize a struct bpf_struct_ops_member_arg_info according to type
+ * info of the arguments of a stub function. (Check kCFI for more
+ * information about stub functions.)
+ *
+ * Each member in the struct_ops type has a struct
+ * bpf_struct_ops_member_arg_info to provide an array of struct
+ * bpf_ctx_arg_aux, which in turn provides the information that used by the
+ * verifier to check the arguments of the BPF struct_ops program assigned
+ * to the member. Here, we only care about the arguments that are marked as
+ * __nullable.
+ *
+ * The array of struct bpf_ctx_arg_aux is eventually assigned to
+ * prog->aux->ctx_arg_info of BPF struct_ops programs and passed to the
+ * verifier. (See check_struct_ops_btf_id())
+ *
+ * member_arg_info->arg_info will be the list of struct bpf_ctx_arg_aux if
+ * success. If fails, it will be kept untouched.
+ */
+static int prepare_arg_info(struct btf *btf,
+ const char *st_ops_name,
+ const char *member_name,
+ const struct btf_type *func_proto,
+ struct bpf_struct_ops_member_arg_info *member_arg_info)
+{
+ const struct btf_type *stub_func_proto, *pointed_type;
+ const struct btf_param *args, *member_args;
+ struct bpf_ctx_arg_aux *arg_info, *ai_buf;
+ u32 nargs, arg_no, arg_info_cnt = 0;
+ const char *arg_name;
+ s32 arg_btf_id;
+ int offset;
+
+ stub_func_proto = find_stub_func_proto(btf, st_ops_name, member_name);
+ if (!stub_func_proto)
+ return 0;
+
+ args = btf_params(stub_func_proto);
+ nargs = btf_type_vlen(stub_func_proto);
+ if (nargs != btf_type_vlen(func_proto)) {
+ pr_warn("the number of arguments of the stub function %s__%s does not match the number of arguments of the member %s of struct %s\n",
+ st_ops_name, member_name, member_name, st_ops_name);
+ return -EINVAL;
+ }
+
+ member_args = btf_params(func_proto);
hmm... the "member_args" naming makes me come back here a few times to figure
out "member_args" is the original func_proto or the stub func_proto.
How about using a similar convention like you did for func_proto: "func_proto"
means the original func_proto and "stub_func_proto" means the stub func_proto,
so something like:
"args" means the args of original func_proto and
"stub_args" means the args of the stub_func_proto ?
+
+ ai_buf = kcalloc(nargs, sizeof(*ai_buf), GFP_KERNEL);
hmm... instead of ai, lets use a fuller name here like arg_info_buf.
+ if (!ai_buf)
+ return -ENOMEM;
+
+ for (arg_no = 0; arg_no < nargs; arg_no++) {
+ /* Skip arguments that is not suffixed with
+ * "__nullable".
+ */
+ arg_name = btf_name_by_offset(btf,
+ args[arg_no].name_off);
+ if (!match_nullable_suffix(arg_name))
+ continue;
+
+ /* Should be a pointer to struct, array, scalar, or enum */
+ pointed_type = btf_type_resolve_ptr(btf,
+ member_args[arg_no].type,
+ &arg_btf_id);
+ if (!pointed_type ||
+ !btf_type_is_struct(pointed_type))
+ goto err_out;
+
+ offset = btf_ctx_arg_offset(btf, stub_func_proto, arg_no);
The original "func_proto" should be used here.
+ if (offset < 0)
+ goto err_out;
+
+ /* Fill the information of the new argument */
+ arg_info = ai_buf + arg_info_cnt++;
nit. just init arg_info = arg_info_buf and advance the arg_info++ and
arg_info_cnt++ after the offset assignment below.
+ arg_info->reg_type =
+ PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL;
+ arg_info->btf_id = arg_btf_id;
+ arg_info->btf = btf;
+ arg_info->offset = offset;
+ }
+
+ if (arg_info_cnt) {
+ member_arg_info->arg_info = ai_buf;
+ member_arg_info->arg_info_cnt = arg_info_cnt;
+ } else {
+ kfree(ai_buf);
+ }
+
+ return 0;
+
+err_out:
+ kfree(ai_buf);
+
+ return -EINVAL;
+}
+
int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
struct btf *btf,
struct bpf_verifier_log *log)
{
+ struct bpf_struct_ops_member_arg_info *member_arg_info;
struct bpf_struct_ops *st_ops = st_ops_desc->st_ops;
const struct btf_member *member;
const struct btf_type *t;
s32 type_id, value_id;
char value_name[128];
const char *mname;
- int i;
+ int i, err;
if (strlen(st_ops->name) + VALUE_PREFIX_LEN >=
sizeof(value_name)) {
@@ -160,6 +305,11 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
if (!is_valid_value_type(btf, value_id, t, value_name))
return -EINVAL;
+ member_arg_info = kcalloc(btf_type_vlen(t), sizeof(*member_arg_info),
+ GFP_KERNEL);
+ if (!member_arg_info)
+ return -ENOMEM;
+
for_each_member(i, t, member) {
const struct btf_type *func_proto;
@@ -167,32 +317,44 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
if (!*mname) {
pr_warn("anon member in struct %s is not supported\n",
st_ops->name);
- return -EOPNOTSUPP;
+ err = -EOPNOTSUPP;
+ goto errout;
}
if (__btf_member_bitfield_size(t, member)) {
pr_warn("bit field member %s in struct %s is not supported\n",
mname, st_ops->name);
- return -EOPNOTSUPP;
+ err = -EOPNOTSUPP;
+ goto errout;
}
func_proto = btf_type_resolve_func_ptr(btf,
member->type,
NULL);
- if (func_proto &&
- btf_distill_func_proto(log, btf,
+ if (!func_proto)
+ continue;
+
+ if (btf_distill_func_proto(log, btf,
func_proto, mname,
&st_ops->func_models[i])) {
pr_warn("Error in parsing func ptr %s in struct %s\n",
mname, st_ops->name);
- return -EINVAL;
+ err = -EINVAL;
+ goto errout;
}
+
+ err = prepare_arg_info(btf, st_ops->name, mname,
+ func_proto,
+ member_arg_info + i);
+ if (err)
+ goto errout;
}
if (st_ops->init(btf)) {
pr_warn("Error in init bpf_struct_ops %s\n",
st_ops->name);
- return -EINVAL;
+ err = -EINVAL;
+ goto errout;
}
st_ops_desc->type_id = type_id;
@@ -200,7 +362,16 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
st_ops_desc->value_id = value_id;
st_ops_desc->value_type = btf_type_by_id(btf, value_id);
+ st_ops_desc->member_arg_info = member_arg_info;
+
return 0;
+
+errout:
+ while (i > 0)
+ kfree(member_arg_info[--i].arg_info);
+ kfree(member_arg_info);
+
+ return err;
}
static int bpf_struct_ops_map_get_next_key(struct bpf_map *map, void *key,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index aa72674114af..6df390ade2c0 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1699,6 +1699,21 @@ static void btf_free_struct_meta_tab(struct btf *btf)
static void btf_free_struct_ops_tab(struct btf *btf)
{
struct btf_struct_ops_tab *tab = btf->struct_ops_tab;
+ struct bpf_struct_ops_member_arg_info *ma_info;
Please try to stay consistent with the variable naming in the same patch. The
other of this patch is using the "member_arg_info" name.
May be just use "arg_infos" everywhere.
+ int i, j;
+
+ if (!tab)
+ return;
+
+ for (i = 0; i < tab->cnt; i++) {
+ ma_info = tab->ops[i].member_arg_info;
+ if (!ma_info)
+ continue;
+
+ for (j = 0; j < btf_type_vlen(tab->ops[i].type); j++)
+ kfree(ma_info[j].arg_info);
+ kfree(ma_info);
Lets refactor this part out to "bpf_struct_ops_desc_release(struct
bpf_struct_ops_desc *)" such that it can be reused with the "errout" path of the
"bpf_struct_ops_desc_init()" above.
+ }
kfree(tab);
btf->struct_ops_tab = NULL;
@@ -6130,6 +6145,31 @@ static bool prog_args_trusted(const struct bpf_prog *prog)
}
}
+int btf_ctx_arg_offset(struct btf *btf, const struct btf_type *func_proto,
+ u32 arg_no)
+{
+ const struct btf_param *args;
+ const struct btf_type *t;
+ int off = 0, i;
+ u32 sz, nargs;
+
+ nargs = btf_type_vlen(func_proto);
+ /* It is the return value if arg_no == nargs */
+ if (arg_no > nargs)
+ return -EINVAL;
+
+ args = btf_params(func_proto);
+ for (i = 0; i < arg_no; i++) {
+ t = btf_type_by_id(btf, args[i].type);
+ t = btf_resolve_size(btf, t, &sz);
+ if (IS_ERR(t))
+ return -EINVAL;
+ off += roundup(sz, 8);
+ }
+
+ return off;
+}
+
bool btf_ctx_access(int off, int size, enum bpf_access_type type,
const struct bpf_prog *prog,
struct bpf_insn_access_aux *info)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 64fa188d00ad..8d7e761cda0d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20433,6 +20433,12 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
}
}
+ /* btf_ctx_access() used this to provide argument type info */
+ prog->aux->ctx_arg_info =
+ st_ops_desc->member_arg_info[member_idx].arg_info;
+ prog->aux->ctx_arg_info_size =
+ st_ops_desc->member_arg_info[member_idx].arg_info_cnt;
+
prog->aux->attach_func_proto = func_proto;
prog->aux->attach_func_name = mname;
env->ops = st_ops->verifier_ops;
