On Thu, Sep 8, 2022 at 1:10 AM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
>
> 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;
Let's return NULL for void* type.
>
> - if (bpf_dynptr_is_rdonly(ptr))
> + if (writable && bpf_dynptr_is_rdonly(ptr))
> return 0;
ditto
>
> 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);
Let's use __func__ so we don't have to change this again.
WARN_ONCE(true, "%s: unknown dynptr type %d\n", __func__, type);
Thanks,
Song
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