On Thu, Sep 8, 2022 at 1:07 AM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
>
> Add two new helper functions: bpf_dynptr_is_null and
> bpf_dynptr_is_rdonly.
>
> bpf_dynptr_is_null returns true if the dynptr is null / invalid
> (determined by whether ptr->data is NULL), else false if
> the dynptr is a valid dynptr.
>
> bpf_dynptr_is_rdonly returns true if the dynptr is read-only,
> else false if the dynptr is read-writable.
Might be a dump question.. Can we just let the bpf program to
access struct bpf_dynptr? Using a helper for this feel like an
overkill.
Thanks,
Song
>
> Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 20 ++++++++++++++++++
> kernel/bpf/helpers.c | 37 +++++++++++++++++++++++++++++++---
> scripts/bpf_doc.py | 3 +++
> tools/include/uapi/linux/bpf.h | 20 ++++++++++++++++++
> 4 files changed, 77 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 3b054553be30..90b6d0744df2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5467,6 +5467,24 @@ union bpf_attr {
> * Return
> * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if
> * trying to trim more bytes than the size of the dynptr.
> + *
> + * bool bpf_dynptr_is_null(struct bpf_dynptr *ptr)
> + * Description
> + * Determine whether a dynptr is null / invalid.
> + *
> + * *ptr* must be an initialized dynptr.
> + * Return
> + * True if the dynptr is null, else false.
> + *
> + * bool bpf_dynptr_is_rdonly(struct bpf_dynptr *ptr)
> + * Description
> + * Determine whether a dynptr is read-only.
> + *
> + * *ptr* must be an initialized dynptr. If *ptr*
> + * is a null dynptr, this will return false.
> + * Return
> + * True if the dynptr is read-only and a valid dynptr,
> + * else false.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5683,6 +5701,8 @@ union bpf_attr {
> FN(dynptr_data_rdonly), \
> FN(dynptr_advance), \
> FN(dynptr_trim), \
> + FN(dynptr_is_null), \
> + FN(dynptr_is_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 9f356105ab49..8729383d0966 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1398,7 +1398,7 @@ static const struct bpf_func_proto bpf_kptr_xchg_proto = {
> #define DYNPTR_SIZE_MASK 0xFFFFFF
> #define DYNPTR_RDONLY_BIT BIT(31)
>
> -static bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)
> +static bool __bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)
> {
> return ptr->size & DYNPTR_RDONLY_BIT;
> }
> @@ -1539,7 +1539,7 @@ BPF_CALL_5(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *,
> enum bpf_dynptr_type type;
> int err;
>
> - if (!dst->data || bpf_dynptr_is_rdonly(dst))
> + if (!dst->data || __bpf_dynptr_is_rdonly(dst))
> return -EINVAL;
>
> err = bpf_dynptr_check_off_len(dst, offset, len);
> @@ -1592,7 +1592,7 @@ void *__bpf_dynptr_data(struct bpf_dynptr_kern *ptr, u32 offset, u32 len, bool w
> if (err)
> return 0;
>
> - if (writable && bpf_dynptr_is_rdonly(ptr))
> + if (writable && __bpf_dynptr_is_rdonly(ptr))
> return 0;
>
> type = bpf_dynptr_get_type(ptr);
> @@ -1705,6 +1705,33 @@ static const struct bpf_func_proto bpf_dynptr_trim_proto = {
> .arg2_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_1(bpf_dynptr_is_null, struct bpf_dynptr_kern *, ptr)
> +{
> + return !ptr->data;
> +}
> +
> +static const struct bpf_func_proto bpf_dynptr_is_null_proto = {
> + .func = bpf_dynptr_is_null,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_DYNPTR,
> +};
> +
> +BPF_CALL_1(bpf_dynptr_is_rdonly, struct bpf_dynptr_kern *, ptr)
> +{
> + if (!ptr->data)
> + return 0;
> +
> + return __bpf_dynptr_is_rdonly(ptr);
> +}
> +
> +static const struct bpf_func_proto bpf_dynptr_is_rdonly_proto = {
> + .func = bpf_dynptr_is_rdonly,
> + .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;
> @@ -1781,6 +1808,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
> return &bpf_dynptr_advance_proto;
> case BPF_FUNC_dynptr_trim:
> return &bpf_dynptr_trim_proto;
> + case BPF_FUNC_dynptr_is_null:
> + return &bpf_dynptr_is_null_proto;
> + case BPF_FUNC_dynptr_is_rdonly:
> + return &bpf_dynptr_is_rdonly_proto;
> default:
> break;
> }
> diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
> index d5c389df6045..ecd227c2ea34 100755
> --- a/scripts/bpf_doc.py
> +++ b/scripts/bpf_doc.py
> @@ -691,6 +691,7 @@ class PrinterHelpers(Printer):
> 'int',
> 'long',
> 'unsigned long',
> + 'bool',
>
> '__be16',
> '__be32',
> @@ -761,6 +762,8 @@ class PrinterHelpers(Printer):
> header = '''\
> /* This is auto-generated file. See bpf_doc.py for details. */
>
> +#include <stdbool.h>
> +
> /* Forward declarations of BPF structs */'''
>
> print(header)
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 3b054553be30..90b6d0744df2 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -5467,6 +5467,24 @@ union bpf_attr {
> * Return
> * 0 on success, -EINVAL if the dynptr is invalid, -ERANGE if
> * trying to trim more bytes than the size of the dynptr.
> + *
> + * bool bpf_dynptr_is_null(struct bpf_dynptr *ptr)
> + * Description
> + * Determine whether a dynptr is null / invalid.
> + *
> + * *ptr* must be an initialized dynptr.
> + * Return
> + * True if the dynptr is null, else false.
> + *
> + * bool bpf_dynptr_is_rdonly(struct bpf_dynptr *ptr)
> + * Description
> + * Determine whether a dynptr is read-only.
> + *
> + * *ptr* must be an initialized dynptr. If *ptr*
> + * is a null dynptr, this will return false.
> + * Return
> + * True if the dynptr is read-only and a valid dynptr,
> + * else false.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5683,6 +5701,8 @@ union bpf_attr {
> FN(dynptr_data_rdonly), \
> FN(dynptr_advance), \
> FN(dynptr_trim), \
> + FN(dynptr_is_null), \
> + FN(dynptr_is_rdonly), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> --
> 2.30.2
>
