On Fri, Apr 1, 2022 at 7:00 PM Joanne Koong <joannekoong@xxxxxx> wrote:
>
> From: Joanne Koong <joannelkoong@xxxxxxxxx>
>
> This patch adds two helper functions, bpf_dynptr_read and
> bpf_dynptr_write:
>
> long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset);
>
> long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len);
>
> The dynptr passed into these functions must be valid dynptrs that have
> been initialized.
>
> Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> ---
> include/linux/bpf.h | 6 ++++
> include/uapi/linux/bpf.h | 18 +++++++++++
> kernel/bpf/helpers.c | 56 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 18 +++++++++++
> 4 files changed, 98 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index e0fcff9f2aee..cded9753fb7f 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2426,6 +2426,12 @@ enum bpf_dynptr_type {
> #define DYNPTR_MAX_SIZE ((1UL << 28) - 1)
> #define DYNPTR_SIZE_MASK 0xFFFFFFF
> #define DYNPTR_TYPE_SHIFT 29
> +#define DYNPTR_RDONLY_BIT BIT(28)
> +
> +static inline bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)
> +{
> + return ptr->size & DYNPTR_RDONLY_BIT;
> +}
>
> static inline enum bpf_dynptr_type bpf_dynptr_get_type(struct bpf_dynptr_kern *ptr)
> {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 6a57d8a1b882..16a35e46be90 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5175,6 +5175,22 @@ union bpf_attr {
> * After this operation, *ptr* will be an invalidated dynptr.
> * Return
> * Void.
> + *
> + * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
> + * Description
> + * Read *len* bytes from *src* into *dst*, starting from *offset*
> + * into *dst*.
> + * Return
> + * 0 on success, -EINVAL if *offset* + *len* exceeds the length
> + * of *src*'s data or if *src* is an invalid dynptr.
> + *
> + * long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len)
> + * Description
> + * Write *len* bytes from *src* into *dst*, starting from *offset*
> + * into *dst*.
> + * Return
> + * 0 on success, -EINVAL if *offset* + *len* exceeds the length
> + * of *dst*'s data or if *dst* is not writeable.
Did you plan to also add a helper to copy from one dynptr to another?
Something like
long bpf_dynptr_copy(struct bpf_dynptr *dst, struct bpf_dyn_ptr *src, u32 len) ?
Otherwise there won't be any way to copy memory from malloc'ed range
to ringbuf, for example, without doing intermediate copy. Not sure
what to do about extra offsets...
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5374,6 +5390,8 @@ union bpf_attr {
> FN(dynptr_from_mem), \
> FN(malloc), \
> FN(free), \
> + FN(dynptr_read), \
> + FN(dynptr_write), \
> /* */
>
> /* 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 ed5a7d9d0a18..7ec20e79928e 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1412,6 +1412,58 @@ const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
> .arg3_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT,
> };
>
> +BPF_CALL_4(bpf_dynptr_read, void *, dst, u32, len, struct bpf_dynptr_kern *, src, u32, offset)
> +{
> + int err;
> +
> + if (!src->data)
> + return -EINVAL;
> +
> + err = bpf_dynptr_check_off_len(src, offset, len);
you defined this function in patch #3, but didn't use it there. Let's
move the definition into this patch?
> + if (err)
> + return err;
> +
> + memcpy(dst, src->data + src->offset + offset, len);
> +
> + return 0;
> +}
> +
[...]
