On Thu, Apr 28, 2022 at 2:12 PM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
>
> 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 | 16 ++++++++++
> include/uapi/linux/bpf.h | 19 ++++++++++++
> kernel/bpf/helpers.c | 56 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 19 ++++++++++++
> 4 files changed, 110 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 10efbec99e93..b276dbf942dd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2387,6 +2387,12 @@ enum bpf_dynptr_type {
> #define DYNPTR_SIZE_MASK 0xFFFFFF
> #define DYNPTR_TYPE_SHIFT 28
> #define DYNPTR_TYPE_MASK 0x7
> +#define DYNPTR_RDONLY_BIT BIT(31)
> +
> +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)
> {
> @@ -2408,6 +2414,16 @@ static inline int bpf_dynptr_check_size(u32 size)
> return size > DYNPTR_MAX_SIZE ? -E2BIG : 0;
> }
>
> +static inline int bpf_dynptr_check_off_len(struct bpf_dynptr_kern *ptr, u32 offset, u32 len)
> +{
> + u32 capacity = bpf_dynptr_get_size(ptr) - ptr->offset;
didn't you specify that size excludes offset, so size is a capacity?
+ /* Size represents the number of usable bytes in the dynptr.
+ * If for example the offset is at 200 for a malloc dynptr with
+ * allocation size 256, the number of usable bytes is 56.
> +
> + if (len > capacity || offset > capacity - len)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> void bpf_dynptr_init(struct bpf_dynptr_kern *ptr, void *data, enum bpf_dynptr_type type,
> u32 offset, u32 size);
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 679f960d2514..2d539930b7b2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5209,6 +5209,23 @@ union bpf_attr {
> * 'bpf_ringbuf_discard'.
> * Return
> * Nothing. Always succeeds.
> + *
> + * 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 *src*.
> + * Return
> + * 0 on success, -EINVAL if *offset* + *len* exceeds the length
this sounds more like E2BIG ?
> + * of *src*'s data or if *src* is an invalid dynptr.
> + *
[...]
