Add two new helper functions: bpf_dynptr_trim and bpf_dynptr_advance.
bpf_dynptr_trim decreases the size of a dynptr by the specified
number of bytes (offset remains the same). bpf_dynptr_advance advances
the offset of the dynptr by the specified number of bytes (size
decreases correspondingly).
One example where trimming / advancing the dynptr may useful is for
hashing. If the dynptr points to a larger struct, it is possible to hash
an individual field within the struct through dynptrs by using
bpf_dynptr_advance+trim.
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 18 +++++++++
kernel/bpf/helpers.c | 67 ++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 18 +++++++++
3 files changed, 103 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a9bb98365031..c2d915601484 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5537,6 +5537,22 @@ union bpf_attr {
* *flags* is currently unused, it must be 0 for now.
* Return
* 0 on success, -EINVAL if flags is not 0.
+ *
+ * long bpf_dynptr_advance(struct bpf_dynptr *ptr, u32 len)
+ * Description
+ * Advance a dynptr's internal offset by *len* bytes.
+ * Return
+ * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if *len*
+ * exceeds the bounds of the dynptr.
+ *
+ * long bpf_dynptr_trim(struct bpf_dynptr *ptr, u32 len)
+ * Description
+ * Trim the size of memory pointed to by the dynptr by *len* bytes.
+ *
+ * The offset is unmodified.
+ * Return
+ * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if
+ * trying to trim more bytes than the size of the dynptr.
*/
#define ___BPF_FUNC_MAPPER(FN, ctx...) \
FN(unspec, 0, ##ctx) \
@@ -5753,6 +5769,8 @@ union bpf_attr {
FN(cgrp_storage_delete, 211, ##ctx) \
FN(dynptr_from_skb, 212, ##ctx) \
FN(dynptr_from_xdp, 213, ##ctx) \
+ FN(dynptr_advance, 214, ##ctx) \
+ FN(dynptr_trim, 215, ##ctx) \
/* */
/* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3a9c8814aaf6..fa3989047ff6 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1429,6 +1429,13 @@ u32 bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr)
return ptr->size & DYNPTR_SIZE_MASK;
}
+static void bpf_dynptr_set_size(struct bpf_dynptr_kern *ptr, u32 new_size)
+{
+ u32 metadata = ptr->size & ~DYNPTR_SIZE_MASK;
+
+ ptr->size = new_size | metadata;
+}
+
int bpf_dynptr_check_size(u32 size)
{
return size > DYNPTR_MAX_SIZE ? -E2BIG : 0;
@@ -1640,6 +1647,62 @@ static const struct bpf_func_proto bpf_dynptr_data_proto = {
.arg3_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
};
+/* For dynptrs, the offset may only be advanced and the size may only be decremented */
+static int bpf_dynptr_adjust(struct bpf_dynptr_kern *ptr, u32 off_inc, u32 sz_dec)
+{
+ u32 size;
+
+ if (!ptr->data)
+ return -EINVAL;
+
+ size = bpf_dynptr_get_size(ptr);
+
+ if (sz_dec > size)
+ return -ERANGE;
+
+ if (off_inc) {
+ u32 new_off;
+
+ if (off_inc > size)
+ return -ERANGE;
+
+ if (check_add_overflow(ptr->offset, off_inc, &new_off))
+ return -ERANGE;
+
+ ptr->offset = new_off;
+ }
+
+ bpf_dynptr_set_size(ptr, size - sz_dec);
+
+ return 0;
+}
+
+BPF_CALL_2(bpf_dynptr_advance, struct bpf_dynptr_kern *, ptr, u32, len)
+{
+ return bpf_dynptr_adjust(ptr, len, len);
+}
+
+static const struct bpf_func_proto bpf_dynptr_advance_proto = {
+ .func = bpf_dynptr_advance,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_DYNPTR,
+ .arg2_type = ARG_ANYTHING,
+};
+
+BPF_CALL_2(bpf_dynptr_trim, struct bpf_dynptr_kern *, ptr, u32, len)
+{
+ return bpf_dynptr_adjust(ptr, 0, len);
+}
+
+static const struct bpf_func_proto bpf_dynptr_trim_proto = {
+ .func = bpf_dynptr_trim,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_DYNPTR,
+ .arg2_type = ARG_ANYTHING,
+};
+
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;
@@ -1744,6 +1807,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
return &bpf_dynptr_write_proto;
case BPF_FUNC_dynptr_data:
return &bpf_dynptr_data_proto;
+ case BPF_FUNC_dynptr_advance:
+ return &bpf_dynptr_advance_proto;
+ case BPF_FUNC_dynptr_trim:
+ return &bpf_dynptr_trim_proto;
#ifdef CONFIG_CGROUPS
case BPF_FUNC_cgrp_storage_get:
return &bpf_cgrp_storage_get_proto;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a9bb98365031..c2d915601484 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5537,6 +5537,22 @@ union bpf_attr {
* *flags* is currently unused, it must be 0 for now.
* Return
* 0 on success, -EINVAL if flags is not 0.
+ *
+ * long bpf_dynptr_advance(struct bpf_dynptr *ptr, u32 len)
+ * Description
+ * Advance a dynptr's internal offset by *len* bytes.
+ * Return
+ * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if *len*
+ * exceeds the bounds of the dynptr.
+ *
+ * long bpf_dynptr_trim(struct bpf_dynptr *ptr, u32 len)
+ * Description
+ * Trim the size of memory pointed to by the dynptr by *len* bytes.
+ *
+ * The offset is unmodified.
+ * Return
+ * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if
+ * trying to trim more bytes than the size of the dynptr.
*/
#define ___BPF_FUNC_MAPPER(FN, ctx...) \
FN(unspec, 0, ##ctx) \
@@ -5753,6 +5769,8 @@ union bpf_attr {
FN(cgrp_storage_delete, 211, ##ctx) \
FN(dynptr_from_skb, 212, ##ctx) \
FN(dynptr_from_xdp, 213, ##ctx) \
+ FN(dynptr_advance, 214, ##ctx) \
+ FN(dynptr_trim, 215, ##ctx) \
/* */
/* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
--
2.30.2
