[PATCH bpf-next v1 4/8] bpf: Add bpf_dynptr_get_size and bpf_dynptr_get_offset

[Joanne Koong <joannelkoong@gmail.com>]

Add two new helper functions: bpf_dynptr_get_size and
bpf_dynptr_get_offset.

bpf_dynptr_get_size returns the number of usable bytes in a dynptr and
bpf_dynptr_get_offset returns the current offset into the dynptr.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/uapi/linux/bpf.h       | 25 ++++++++++++++++++++
 kernel/bpf/helpers.c           | 42 ++++++++++++++++++++++++++++++----
 tools/include/uapi/linux/bpf.h | 25 ++++++++++++++++++++
 3 files changed, 88 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 90b6d0744df2..4ca07cf500d2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5485,6 +5485,29 @@ union bpf_attr {
  *	Return
  *		True if the dynptr is read-only and a valid dynptr,
  *		else false.
+ *
+ * long bpf_dynptr_get_size(struct bpf_dynptr *ptr)
+ *	Description
+ *		Get the size of *ptr*.
+ *
+ *		Size refers to the number of usable bytes. For example,
+ *		if *ptr* was initialized with 100 bytes and its
+ *		offset was advanced by 40 bytes, then the size will be
+ *		60 bytes.
+ *
+ *		*ptr* must be an initialized dynptr.
+ *	Return
+ *		The size of the dynptr on success, -EINVAL if the dynptr is
+ *		invalid.
+ *
+ * long bpf_dynptr_get_offset(struct bpf_dynptr *ptr)
+ *	Description
+ *		Get the offset of the dynptr.
+ *
+ *		*ptr* must be an initialized dynptr.
+ *	Return
+ *		The offset of the dynptr on success, -EINVAL if the dynptr is
+ *		invalid.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5703,6 +5726,8 @@ union bpf_attr {
 	FN(dynptr_trim),		\
 	FN(dynptr_is_null),		\
 	FN(dynptr_is_rdonly),		\
+	FN(dynptr_get_size),		\
+	FN(dynptr_get_offset),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8729383d0966..62ed27444b73 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1418,7 +1418,7 @@ static enum bpf_dynptr_type bpf_dynptr_get_type(const struct bpf_dynptr_kern *pt
 	return (ptr->size & ~(DYNPTR_RDONLY_BIT)) >> DYNPTR_TYPE_SHIFT;
 }
 
-static u32 bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr)
+static u32 __bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr)
 {
 	return ptr->size & DYNPTR_SIZE_MASK;
 }
@@ -1451,7 +1451,7 @@ void bpf_dynptr_set_null(struct bpf_dynptr_kern *ptr)
 
 static int bpf_dynptr_check_off_len(struct bpf_dynptr_kern *ptr, u32 offset, u32 len)
 {
-	u32 size = bpf_dynptr_get_size(ptr);
+	u32 size = __bpf_dynptr_get_size(ptr);
 
 	if (len > size || offset > size - len)
 		return -E2BIG;
@@ -1660,7 +1660,7 @@ BPF_CALL_2(bpf_dynptr_advance, struct bpf_dynptr_kern *, ptr, u32, len)
 	if (!ptr->data)
 		return -EINVAL;
 
-	size = bpf_dynptr_get_size(ptr);
+	size = __bpf_dynptr_get_size(ptr);
 
 	if (len > size)
 		return -ERANGE;
@@ -1687,7 +1687,7 @@ BPF_CALL_2(bpf_dynptr_trim, struct bpf_dynptr_kern *, ptr, u32, len)
 	if (!ptr->data)
 		return -EINVAL;
 
-	size = bpf_dynptr_get_size(ptr);
+	size = __bpf_dynptr_get_size(ptr);
 
 	if (len > size)
 		return -ERANGE;
@@ -1732,6 +1732,36 @@ static const struct bpf_func_proto bpf_dynptr_is_rdonly_proto = {
 	.arg1_type	= ARG_PTR_TO_DYNPTR,
 };
 
+BPF_CALL_1(bpf_dynptr_get_size, struct bpf_dynptr_kern *, ptr)
+{
+	if (!ptr->data)
+		return -EINVAL;
+
+	return __bpf_dynptr_get_size(ptr);
+}
+
+static const struct bpf_func_proto bpf_dynptr_get_size_proto = {
+	.func		= bpf_dynptr_get_size,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_DYNPTR,
+};
+
+BPF_CALL_1(bpf_dynptr_get_offset, struct bpf_dynptr_kern *, ptr)
+{
+	if (!ptr->data)
+		return -EINVAL;
+
+	return ptr->offset;
+}
+
+static const struct bpf_func_proto bpf_dynptr_get_offset_proto = {
+	.func		= bpf_dynptr_get_offset,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_DYNPTR,
+};
+
 const struct bpf_func_proto bpf_get_current_task_proto __weak;
 const struct bpf_func_proto bpf_get_current_task_btf_proto __weak;
 const struct bpf_func_proto bpf_probe_read_user_proto __weak;
@@ -1812,6 +1842,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_dynptr_is_null_proto;
 	case BPF_FUNC_dynptr_is_rdonly:
 		return &bpf_dynptr_is_rdonly_proto;
+	case BPF_FUNC_dynptr_get_size:
+		return &bpf_dynptr_get_size_proto;
+	case BPF_FUNC_dynptr_get_offset:
+		return &bpf_dynptr_get_offset_proto;
 	default:
 		break;
 	}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 90b6d0744df2..4ca07cf500d2 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5485,6 +5485,29 @@ union bpf_attr {
  *	Return
  *		True if the dynptr is read-only and a valid dynptr,
  *		else false.
+ *
+ * long bpf_dynptr_get_size(struct bpf_dynptr *ptr)
+ *	Description
+ *		Get the size of *ptr*.
+ *
+ *		Size refers to the number of usable bytes. For example,
+ *		if *ptr* was initialized with 100 bytes and its
+ *		offset was advanced by 40 bytes, then the size will be
+ *		60 bytes.
+ *
+ *		*ptr* must be an initialized dynptr.
+ *	Return
+ *		The size of the dynptr on success, -EINVAL if the dynptr is
+ *		invalid.
+ *
+ * long bpf_dynptr_get_offset(struct bpf_dynptr *ptr)
+ *	Description
+ *		Get the offset of the dynptr.
+ *
+ *		*ptr* must be an initialized dynptr.
+ *	Return
+ *		The offset of the dynptr on success, -EINVAL if the dynptr is
+ *		invalid.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5703,6 +5726,8 @@ union bpf_attr {
 	FN(dynptr_trim),		\
 	FN(dynptr_is_null),		\
 	FN(dynptr_is_rdonly),		\
+	FN(dynptr_get_size),		\
+	FN(dynptr_get_offset),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.30.2