Add a new helper bpf_dynptr_data_rdonly
void *bpf_dynptr_data_rdonly(struct bpf_dynptr *ptr, u32 offset, u32 len);
which gets a read-only pointer to the underlying dynptr data.
This is equivalent to bpf_dynptr_data(), except the pointer returned is
read-only, which allows this to support both read-write and read-only
dynptrs.
One example where this will be useful is for skb dynptrs where the
program type only allows read-only access to packet data. This API will
provide a way to obtain a data slice that can be used for direct reads.
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 15 +++++++++++++++
kernel/bpf/helpers.c | 32 ++++++++++++++++++++++++++------
kernel/bpf/verifier.c | 7 +++++--
tools/include/uapi/linux/bpf.h | 15 +++++++++++++++
4 files changed, 61 insertions(+), 8 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c55c23f25c0f..cce3356765fc 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5439,6 +5439,20 @@ union bpf_attr {
* *flags* is currently unused, it must be 0 for now.
* Return
* 0 on success, -EINVAL if flags is not 0.
+ *
+ * void *bpf_dynptr_data_rdonly(struct bpf_dynptr *ptr, u32 offset, u32 len)
+ * Description
+ * Get a read-only pointer to the underlying dynptr data.
+ *
+ * This is equivalent to **bpf_dynptr_data**\ () except the
+ * pointer returned is read-only, which allows this to support
+ * both read-write and read-only dynptrs. For more details on using
+ * the API, please refer to **bpf_dynptr_data**\ ().
+ * Return
+ * Read-only pointer to the underlying dynptr data, NULL if the
+ * dynptr is invalid or if the offset and length is out of bounds
+ * or in a paged buffer for skb-type dynptrs or across fragments
+ * for xdp-type dynptrs.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5652,6 +5666,7 @@ union bpf_attr {
FN(ktime_get_tai_ns), \
FN(dynptr_from_skb), \
FN(dynptr_from_xdp), \
+ FN(dynptr_data_rdonly), \
/* */
/* 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 befafae34a63..30a59c9e5df3 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1572,7 +1572,7 @@ static const struct bpf_func_proto bpf_dynptr_write_proto = {
.arg5_type = ARG_ANYTHING,
};
-BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
+void *__bpf_dynptr_data(struct bpf_dynptr_kern *ptr, u32 offset, u32 len, bool writable)
{
enum bpf_dynptr_type type;
void *data;
@@ -1585,7 +1585,7 @@ BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len
if (err)
return 0;
- if (bpf_dynptr_is_rdonly(ptr))
+ if (writable && bpf_dynptr_is_rdonly(ptr))
return 0;
type = bpf_dynptr_get_type(ptr);
@@ -1610,13 +1610,31 @@ BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len
/* if the requested data in across fragments, then it cannot
* be accessed directly - bpf_xdp_pointer will return NULL
*/
- return (unsigned long)bpf_xdp_pointer(ptr->data,
- ptr->offset + offset, len);
+ return bpf_xdp_pointer(ptr->data, ptr->offset + offset, len);
default:
- WARN_ONCE(true, "bpf_dynptr_data: unknown dynptr type %d\n", type);
+ WARN_ONCE(true, "__bpf_dynptr_data: unknown dynptr type %d\n", type);
return 0;
}
- return (unsigned long)(data + ptr->offset + offset);
+ return data + ptr->offset + offset;
+}
+
+BPF_CALL_3(bpf_dynptr_data_rdonly, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
+{
+ return (unsigned long)__bpf_dynptr_data(ptr, offset, len, false);
+}
+
+static const struct bpf_func_proto bpf_dynptr_data_rdonly_proto = {
+ .func = bpf_dynptr_data_rdonly,
+ .gpl_only = false,
+ .ret_type = RET_PTR_TO_DYNPTR_MEM_OR_NULL | MEM_RDONLY,
+ .arg1_type = ARG_PTR_TO_DYNPTR,
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
+};
+
+BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
+{
+ return (unsigned long)__bpf_dynptr_data(ptr, offset, len, true);
}
static const struct bpf_func_proto bpf_dynptr_data_proto = {
@@ -1698,6 +1716,8 @@ 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_data_rdonly:
+ return &bpf_dynptr_data_rdonly_proto;
default:
break;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b1f66a1cc690..c312d931359d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -506,7 +506,8 @@ static bool is_ptr_cast_function(enum bpf_func_id func_id)
static bool is_dynptr_ref_function(enum bpf_func_id func_id)
{
- return func_id == BPF_FUNC_dynptr_data;
+ return func_id == BPF_FUNC_dynptr_data ||
+ func_id == BPF_FUNC_dynptr_data_rdonly;
}
static bool helper_multiple_ref_obj_use(enum bpf_func_id func_id,
@@ -7398,6 +7399,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
}
break;
case BPF_FUNC_dynptr_data:
+ case BPF_FUNC_dynptr_data_rdonly:
{
struct bpf_reg_state *reg;
@@ -7495,7 +7497,8 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].type = PTR_TO_MEM | ret_flag;
regs[BPF_REG_0].mem_size = meta.mem_size;
- if (func_id == BPF_FUNC_dynptr_data) {
+ if (func_id == BPF_FUNC_dynptr_data ||
+ func_id == BPF_FUNC_dynptr_data_rdonly) {
if (dynptr_type == BPF_DYNPTR_TYPE_SKB)
regs[BPF_REG_0].type |= DYNPTR_TYPE_SKB;
else if (dynptr_type == BPF_DYNPTR_TYPE_XDP)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c55c23f25c0f..cce3356765fc 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5439,6 +5439,20 @@ union bpf_attr {
* *flags* is currently unused, it must be 0 for now.
* Return
* 0 on success, -EINVAL if flags is not 0.
+ *
+ * void *bpf_dynptr_data_rdonly(struct bpf_dynptr *ptr, u32 offset, u32 len)
+ * Description
+ * Get a read-only pointer to the underlying dynptr data.
+ *
+ * This is equivalent to **bpf_dynptr_data**\ () except the
+ * pointer returned is read-only, which allows this to support
+ * both read-write and read-only dynptrs. For more details on using
+ * the API, please refer to **bpf_dynptr_data**\ ().
+ * Return
+ * Read-only pointer to the underlying dynptr data, NULL if the
+ * dynptr is invalid or if the offset and length is out of bounds
+ * or in a paged buffer for skb-type dynptrs or across fragments
+ * for xdp-type dynptrs.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5652,6 +5666,7 @@ union bpf_attr {
FN(ktime_get_tai_ns), \
FN(dynptr_from_skb), \
FN(dynptr_from_xdp), \
+ FN(dynptr_data_rdonly), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.30.2
