[PATCH 5.15 02/33] bpf: Introduce composable reg, ret and arg types.

Greg Kroah-Hartman
2022-04-29T10:43:54Z

From: Hao Luo <haoluo@google.com>

commit d639b9d13a39cf15639cbe6e8b2c43eb60148a73 upstream.

There are some common properties shared between bpf reg, ret and arg
values. For instance, a value may be a NULL pointer, or a pointer to
a read-only memory. Previously, to express these properties, enumeration
was used. For example, in order to test whether a reg value can be NULL,
reg_type_may_be_null() simply enumerates all types that are possibly
NULL. The problem of this approach is that it's not scalable and causes
a lot of duplication. These properties can be combined, for example, a
type could be either MAYBE_NULL or RDONLY, or both.

This patch series rewrites the layout of reg_type, arg_type and
ret_type, so that common properties can be extracted and represented as
composable flag. For example, one can write

ARG_PTR_TO_MEM | PTR_MAYBE_NULL

which is equivalent to the previous

ARG_PTR_TO_MEM_OR_NULL

The type ARG_PTR_TO_MEM are called "base type" in this patch. Base
types can be extended with flags. A flag occupies the higher bits while
base types sits in the lower bits.

This patch in particular sets up a set of macro for this purpose. The
following patches will rewrite arg_types, ret_types and reg_types
respectively.

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211217003152.48334-2-haoluo@google.com
Cc: stable@vger.kernel.org # 5.15.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/bpf.h | 42 ++++++++++++++++++++++++++++++++++++++++++
include/linux/bpf_verifier.h | 14 ++++++++++++++
2 files changed, 56 insertions(+)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -293,6 +293,29 @@ bool bpf_map_meta_equal(const struct bpf

extern const struct bpf_map_ops bpf_map_offload_ops;

+/* bpf_type_flag contains a set of flags that are applicable to the values of
+ * arg_type, ret_type and reg_type. For example, a pointer value may be null,
+ * or a memory is read-only. We classify types into two categories: base types
+ * and extended types. Extended types are base types combined with a type flag.
+ *
+ * Currently there are no more than 32 base types in arg_type, ret_type and
+ * reg_types.
+ */
+#define BPF_BASE_TYPE_BITS 8
+
+enum bpf_type_flag {
+ /* PTR may be NULL. */
+ PTR_MAYBE_NULL = BIT(0 + BPF_BASE_TYPE_BITS),
+
+ __BPF_TYPE_LAST_FLAG = PTR_MAYBE_NULL,
+};
+
+/* Max number of base types. */
+#define BPF_BASE_TYPE_LIMIT (1UL << BPF_BASE_TYPE_BITS)
+
+/* Max number of all types. */
+#define BPF_TYPE_LIMIT (__BPF_TYPE_LAST_FLAG | (__BPF_TYPE_LAST_FLAG - 1))
+
/* function argument constraints */
enum bpf_arg_type {
ARG_DONTCARE = 0, /* unused argument in helper function */
@@ -339,7 +362,13 @@ enum bpf_arg_type {
ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */
ARG_PTR_TO_TIMER, /* pointer to bpf_timer */
__BPF_ARG_TYPE_MAX,
+
+ /* This must be the last entry. Its purpose is to ensure the enum is
+ * wide enough to hold the higher bits reserved for bpf_type_flag.
+ */
+ __BPF_ARG_TYPE_LIMIT = BPF_TYPE_LIMIT,
};
+static_assert(__BPF_ARG_TYPE_MAX <= BPF_BASE_TYPE_LIMIT);

/* type of values returned from helper functions */
enum bpf_return_type {
@@ -355,7 +384,14 @@ enum bpf_return_type {
RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, /* returns a pointer to a valid memory or a btf_id or NULL */
RET_PTR_TO_MEM_OR_BTF_ID, /* returns a pointer to a valid memory or a btf_id */
RET_PTR_TO_BTF_ID, /* returns a pointer to a btf_id */
+ __BPF_RET_TYPE_MAX,
+
+ /* This must be the last entry. Its purpose is to ensure the enum is
+ * wide enough to hold the higher bits reserved for bpf_type_flag.
+ */
+ __BPF_RET_TYPE_LIMIT = BPF_TYPE_LIMIT,
};
+static_assert(__BPF_RET_TYPE_MAX <= BPF_BASE_TYPE_LIMIT);

/* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
* to in-kernel helper functions and for adjusting imm32 field in BPF_CALL
@@ -457,7 +493,13 @@ enum bpf_reg_type {
PTR_TO_FUNC, /* reg points to a bpf program function */
PTR_TO_MAP_KEY, /* reg points to a map element key */
__BPF_REG_TYPE_MAX,
+
+ /* This must be the last entry. Its purpose is to ensure the enum is
+ * wide enough to hold the higher bits reserved for bpf_type_flag.
+ */
+ __BPF_REG_TYPE_LIMIT = BPF_TYPE_LIMIT,
};
+static_assert(__BPF_REG_TYPE_MAX <= BPF_BASE_TYPE_LIMIT);

/* The information passed from prog-specific *_is_valid_access
* back to the verifier.
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -535,4 +535,18 @@ int bpf_check_attach_target(struct bpf_v
u32 btf_id,
struct bpf_attach_target_info *tgt_info);

+#define BPF_BASE_TYPE_MASK GENMASK(BPF_BASE_TYPE_BITS - 1, 0)
+
+/* extract base type from bpf_{arg, return, reg}_type. */
+static inline u32 base_type(u32 type)
+{
+ return type & BPF_BASE_TYPE_MASK;
+}
+
+/* extract flags from an extended type. See bpf_type_flag in bpf.h. */
+static inline u32 type_flag(u32 type)
+{
+ return type & ~BPF_BASE_TYPE_MASK;
+}
+
#endif /* _LINUX_BPF_VERIFIER_H */