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Message-Id: <20211210172034.13614-1-mcroce@linux.microsoft.com>
Date: Fri, 10 Dec 2021 18:20:34 +0100
From: Matteo Croce <mcroce@...ux.microsoft.com>
To: bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next] bpf: limit bpf_core_types_are_compat() recursion
From: Matteo Croce <mcroce@...rosoft.com>
In userspace, bpf_core_types_are_compat() is a recursive function which
can't be put in the kernel as is.
Limit the recursion depth to 2, to avoid potential stack overflows
in kernel.
Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
---
include/linux/btf.h | 5 +++
kernel/bpf/btf.c | 107 +++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 111 insertions(+), 1 deletion(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index acef6ef28768..03162ae04ace 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -300,6 +300,11 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo(
return (const struct btf_var_secinfo *)(t + 1);
}
+static inline struct btf_param *btf_params(const struct btf_type *t)
+{
+ return (struct btf_param *)(t + 1);
+}
+
#ifdef CONFIG_BPF_SYSCALL
struct bpf_prog;
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 27b7de538697..dcbf127ad6d2 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6418,10 +6418,115 @@ bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist, u32 kfunc_id,
DEFINE_KFUNC_BTF_ID_LIST(bpf_tcp_ca_kfunc_list);
DEFINE_KFUNC_BTF_ID_LIST(prog_test_kfunc_list);
+#define MAX_TYPES_ARE_COMPAT_DEPTH 2
+
+static
+int __bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
+ const struct btf *targ_btf, __u32 targ_id,
+ int level)
+{
+ const struct btf_type *local_type, *targ_type;
+ int depth = 32; /* max recursion depth */
+
+ if (level <= 0)
+ return -EINVAL;
+
+ /* caller made sure that names match (ignoring flavor suffix) */
+ local_type = btf_type_by_id(local_btf, local_id);
+ targ_type = btf_type_by_id(targ_btf, targ_id);
+ if (btf_kind(local_type) != btf_kind(targ_type))
+ return 0;
+
+recur:
+ depth--;
+ if (depth < 0)
+ return -EINVAL;
+
+ local_type = btf_type_skip_modifiers(local_btf, local_id, &local_id);
+ targ_type = btf_type_skip_modifiers(targ_btf, targ_id, &targ_id);
+ if (!local_type || !targ_type)
+ return -EINVAL;
+
+ if (btf_kind(local_type) != btf_kind(targ_type))
+ return 0;
+
+ switch (btf_kind(local_type)) {
+ case BTF_KIND_UNKN:
+ case BTF_KIND_STRUCT:
+ case BTF_KIND_UNION:
+ case BTF_KIND_ENUM:
+ case BTF_KIND_FWD:
+ return 1;
+ case BTF_KIND_INT:
+ /* just reject deprecated bitfield-like integers; all other
+ * integers are by default compatible between each other
+ */
+ return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0;
+ case BTF_KIND_PTR:
+ local_id = local_type->type;
+ targ_id = targ_type->type;
+ goto recur;
+ case BTF_KIND_ARRAY:
+ local_id = btf_array(local_type)->type;
+ targ_id = btf_array(targ_type)->type;
+ goto recur;
+ case BTF_KIND_FUNC_PROTO: {
+ struct btf_param *local_p = btf_params(local_type);
+ struct btf_param *targ_p = btf_params(targ_type);
+ __u16 local_vlen = btf_vlen(local_type);
+ __u16 targ_vlen = btf_vlen(targ_type);
+ int i, err;
+
+ if (local_vlen != targ_vlen)
+ return 0;
+
+ for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
+ btf_type_skip_modifiers(local_btf, local_p->type, &local_id);
+ btf_type_skip_modifiers(targ_btf, targ_p->type, &targ_id);
+ err = __bpf_core_types_are_compat(local_btf, local_id,
+ targ_btf, targ_id,
+ level - 1);
+ if (err <= 0)
+ return err;
+ }
+
+ /* tail recurse for return type check */
+ btf_type_skip_modifiers(local_btf, local_type->type, &local_id);
+ btf_type_skip_modifiers(targ_btf, targ_type->type, &targ_id);
+ goto recur;
+ }
+ default:
+ pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
+ btf_type_str(local_type), local_id, targ_id);
+ return 0;
+ }
+}
+
+/* Check local and target types for compatibility. This check is used for
+ * type-based CO-RE relocations and follow slightly different rules than
+ * 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
+ * kind should match for local and target types (i.e., STRUCT is not
+ * compatible with UNION);
+ * - for ENUMs, the size is ignored;
+ * - for INT, size and signedness are ignored;
+ * - for ARRAY, dimensionality is ignored, element types are checked for
+ * compatibility recursively;
+ * - CONST/VOLATILE/RESTRICT modifiers are ignored;
+ * - TYPEDEFs/PTRs are compatible if types they pointing to are compatible;
+ * - FUNC_PROTOs are compatible if they have compatible signature: same
+ * number of input args and compatible return and argument types.
+ * These rules are not set in stone and probably will be adjusted as we get
+ * more experience with using BPF CO-RE relocations.
+ */
int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
const struct btf *targ_btf, __u32 targ_id)
{
- return -EOPNOTSUPP;
+ return __bpf_core_types_are_compat(local_btf, local_id,
+ targ_btf, targ_id,
+ MAX_TYPES_ARE_COMPAT_DEPTH);
}
static bool bpf_core_is_flavor_sep(const char *s)
--
2.33.1
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