Adding btf_struct_address function that takes 2 BTF objects
and offset as arguments and checks whether object A is nested
in object B on given offset.
This function is be used when checking the helper function
PTR_TO_BTF_ID arguments. If the argument has an offset value,
the btf_struct_address will check if the final address is
the expected BTF ID.
This way we can access nested BTF objects under PTR_TO_BTF_ID
pointer type and pass them to helpers, while they still point
to valid kernel BTF objects.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
include/linux/bpf.h | 3 +++
kernel/bpf/btf.c | 63 ++++++++++++++++++++++++++++++++++++++-----
kernel/bpf/verifier.c | 32 ++++++++++++++--------
3 files changed, 81 insertions(+), 17 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b7d3b5f3dc09..e98c113a5d27 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1283,6 +1283,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
int btf_struct_access(struct bpf_verifier_log *log,
const struct btf_type *t, int off, int size,
u32 *next_btf_id);
+int btf_struct_address(struct bpf_verifier_log *log,
+ const struct btf_type *t,
+ u32 off, u32 id);
int btf_resolve_helper_id(struct bpf_verifier_log *log,
const struct bpf_func_proto *fn, int);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 304369a4c2e2..6924180a19c4 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3829,9 +3829,22 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
return true;
}
-int btf_struct_access(struct bpf_verifier_log *log,
- const struct btf_type *t, int off, int size,
- u32 *next_btf_id)
+enum access_op {
+ ACCESS_NEXT,
+ ACCESS_EXPECT,
+};
+
+struct access_data {
+ enum access_op op;
+ union {
+ u32 *next_btf_id;
+ const struct btf_type *exp_type;
+ };
+};
+
+static int struct_access(struct bpf_verifier_log *log,
+ const struct btf_type *t, int off, int size,
+ struct access_data *data)
{
u32 i, moff, mtrue_end, msize = 0, total_nelems = 0;
const struct btf_type *mtype, *elem_type = NULL;
@@ -3879,8 +3892,7 @@ int btf_struct_access(struct bpf_verifier_log *log,
goto error;
off = (off - moff) % elem_type->size;
- return btf_struct_access(log, elem_type, off, size,
- next_btf_id);
+ return struct_access(log, elem_type, off, size, data);
error:
bpf_log(log, "access beyond struct %s at off %u size %u\n",
@@ -4008,9 +4020,21 @@ int btf_struct_access(struct bpf_verifier_log *log,
/* adjust offset we're looking for */
off -= moff;
+
+ /* We are nexting into another struct,
+ * check if we are crossing expected ID.
+ */
+ if (data->op == ACCESS_EXPECT && !off && t == data->exp_type)
+ return 0;
goto again;
}
+ /* We are interested only in structs for expected ID,
+ * bail out.
+ */
+ if (data->op == ACCESS_EXPECT)
+ return -EINVAL;
+
if (btf_type_is_ptr(mtype)) {
const struct btf_type *stype;
u32 id;
@@ -4024,7 +4048,7 @@ int btf_struct_access(struct bpf_verifier_log *log,
stype = btf_type_skip_modifiers(btf_vmlinux, mtype->type, &id);
if (btf_type_is_struct(stype)) {
- *next_btf_id = id;
+ *data->next_btf_id = id;
return PTR_TO_BTF_ID;
}
}
@@ -4048,6 +4072,33 @@ int btf_struct_access(struct bpf_verifier_log *log,
return -EINVAL;
}
+int btf_struct_access(struct bpf_verifier_log *log,
+ const struct btf_type *t, int off, int size,
+ u32 *next_btf_id)
+{
+ struct access_data data = {
+ .op = ACCESS_NEXT,
+ .next_btf_id = next_btf_id,
+ };
+
+ return struct_access(log, t, off, size, &data);
+}
+
+int btf_struct_address(struct bpf_verifier_log *log,
+ const struct btf_type *t,
+ u32 off, u32 id)
+{
+ struct access_data data = { .op = ACCESS_EXPECT };
+ const struct btf_type *type;
+
+ type = btf_type_by_id(btf_vmlinux, id);
+ if (!type)
+ return -EINVAL;
+
+ data.exp_type = type;
+ return struct_access(log, t, off, 1, &data);
+}
+
int btf_resolve_helper_id(struct bpf_verifier_log *log,
const struct bpf_func_proto *fn, int arg)
{
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b553e4523bd3..bee3da2cd945 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3741,6 +3741,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
{
struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
enum bpf_reg_type expected_type, type = reg->type;
+ const struct btf_type *btf_type;
int err = 0;
if (arg_type == ARG_DONTCARE)
@@ -3820,17 +3821,26 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
expected_type = PTR_TO_BTF_ID;
if (type != expected_type)
goto err_type;
- if (reg->btf_id != meta->btf_id) {
- verbose(env, "Helper has type %s got %s in R%d\n",
- kernel_type_name(meta->btf_id),
- kernel_type_name(reg->btf_id), regno);
-
- return -EACCES;
- }
- if (!tnum_is_const(reg->var_off) || reg->var_off.value || reg->off) {
- verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
- regno);
- return -EACCES;
+ if (reg->off) {
+ btf_type = btf_type_by_id(btf_vmlinux, reg->btf_id);
+ if (btf_struct_address(&env->log, btf_type, reg->off, meta->btf_id)) {
+ verbose(env, "Helper has type %s got %s in R%d, off %d\n",
+ kernel_type_name(meta->btf_id),
+ kernel_type_name(reg->btf_id), regno, reg->off);
+ return -EACCES;
+ }
+ } else {
+ if (reg->btf_id != meta->btf_id) {
+ verbose(env, "Helper has type %s got %s in R%d\n",
+ kernel_type_name(meta->btf_id),
+ kernel_type_name(reg->btf_id), regno);
+ return -EACCES;
+ }
+ if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
+ verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
+ regno);
+ return -EACCES;
+ }
}
} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
if (meta->func_id == BPF_FUNC_spin_lock) {
--
2.25.4
