On Fri, Feb 21, 2025 at 2:14 PM Mykyta Yatsenko
<mykyta.yatsenko5@xxxxxxxxx> wrote:
>
> From: Mykyta Yatsenko <yatsenko@xxxxxxxx>
>
> Introducing bpf_dynptr_copy kfunc allowing copying data from one dynptr to
> another. This functionality is useful in scenarios such as capturing XDP
> data to a ring buffer.
> The implementation consists of 4 branches:
> * A fast branch for contiguous buffer capacity in both source and
> destination dynptrs
> * 3 branches utilizing __bpf_dynptr_read and __bpf_dynptr_write to copy
> data to/from non-contiguous buffer
>
> Signed-off-by: Mykyta Yatsenko <yatsenko@xxxxxxxx>
> ---
> kernel/bpf/helpers.c | 55 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
LGTM, a bit of unnecessary code I pointed out, but I like how minimal
and clean all this looks, and completely reused pre-existing APIs.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 6600aa4492ec..264afa0effb0 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2770,6 +2770,60 @@ __bpf_kfunc int bpf_dynptr_clone(const struct bpf_dynptr *p,
> return 0;
> }
>
> +/**
> + * bpf_dynptr_copy() - Copy data from one dynptr to another.
> + * @dst_ptr: Destination dynptr - where data should be copied to
> + * @dst_off: Offset into the destination dynptr
> + * @src_ptr: Source dynptr - where data should be copied from
> + * @src_off: Offset into the source dynptr
> + * @size: Length of the data to copy from source to destination
> + *
> + * Copies data from source dynptr to destination dynptr
> + */
> +__bpf_kfunc int bpf_dynptr_copy(struct bpf_dynptr *dst_ptr, u32 dst_off,
> + struct bpf_dynptr *src_ptr, u32 src_off, u32 size)
> +{
> + struct bpf_dynptr_kern *dst = (struct bpf_dynptr_kern *)dst_ptr;
> + struct bpf_dynptr_kern *src = (struct bpf_dynptr_kern *)src_ptr;
> + void *src_slice, *dst_slice;
> + char buf[256];
> + u32 off;
> +
> + src_slice = bpf_dynptr_slice(src_ptr, src_off, NULL, size);
> + dst_slice = bpf_dynptr_slice_rdwr(dst_ptr, dst_off, NULL, size);
> +
> + if (src_slice && dst_slice) {
> + memmove(dst_slice, src_slice, size);
> + return 0;
> + }
> +
> + if (src_slice)
> + return __bpf_dynptr_write(dst, dst_off, src_slice, size, 0);
> +
> + if (dst_slice)
> + return __bpf_dynptr_read(dst_slice, size, src, src_off, 0);
> +
> + if (bpf_dynptr_check_off_len(dst, dst_off, size) ||
> + bpf_dynptr_check_off_len(src, src_off, size))
__bpf_dynptr_read() and __bpf_dynptr_write() do these checks, so
either it's unnecessary and we should keep all the sanity checking to
dynptr_{read,write}, OR we ensure __bpf_dynptr_read/write don't do
sanity checking every single time and we do full checking here, but
then we'll need to also check !dst->data ||
__bpf_dynptr_is_rdonly(dst)
I think for now, I'd keep all the sanity checking to read/write and
not over-optimize. So let's drop these checks?
pw-bot: cr
> + return -E2BIG;
> +
> + off = 0;
> + while (off < size) {
> + u32 chunk_sz = min_t(u32, sizeof(buf), size - off);
> + int err = 0;
nit: unnecessary = 0 initialization, you are overwriting it immediately below
> +
> + err = __bpf_dynptr_read(buf, chunk_sz, src, src_off + off, 0);
> + if (err)
> + return err;
> + err = __bpf_dynptr_write(dst, dst_off + off, buf, chunk_sz, 0);
> + if (err)
> + return err;
> +
> + off += chunk_sz;
> + }
> + return 0;
> +}
> +
> __bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj)
> {
> return obj;
> @@ -3218,6 +3272,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
> BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> BTF_ID_FLAGS(func, bpf_dynptr_size)
> BTF_ID_FLAGS(func, bpf_dynptr_clone)
> +BTF_ID_FLAGS(func, bpf_dynptr_copy)
> #ifdef CONFIG_NET
> BTF_ID_FLAGS(func, bpf_modify_return_test_tp)
> #endif
> --
> 2.48.1
>
