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Date: Thu, 28 Oct 2021 00:53:09 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
netdev@...r.kernel.org
Cc: lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
ast@...nel.org, shayagr@...zon.com, john.fastabend@...il.com,
dsahern@...nel.org, brouer@...hat.com, echaudro@...hat.com,
jasowang@...hat.com, alexander.duyck@...il.com, saeed@...nel.org,
maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
tirthendu.sarkar@...el.com, toke@...hat.com
Subject: Re: [PATCH v16 bpf-next 19/20] net: xdp: introduce bpf_xdp_pointer
utility routine
On 10/15/21 3:08 PM, Lorenzo Bianconi wrote:
[...]
> +static void *bpf_xdp_pointer(struct xdp_buff *xdp, u32 offset,
> + u32 len, void *buf)
> +{
> + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> + u32 size = xdp->data_end - xdp->data;
> + void *addr = xdp->data;
> + u32 frame_sz = size;
> + int i;
> +
> + if (xdp_buff_is_mb(xdp))
> + frame_sz += sinfo->xdp_frags_size;
> +
> + if (offset + len > frame_sz)
> + return ERR_PTR(-EINVAL);
Given offset is ARG_ANYTHING, the above could overflow. In bpf_skb_*_bytes() we
guard with offset > 0xffff.
> + if (offset < size) /* linear area */
> + goto out;
> +
> + offset -= size;
> + for (i = 0; i < sinfo->nr_frags; i++) { /* paged area */
> + u32 frag_size = skb_frag_size(&sinfo->frags[i]);
> +
> + if (offset < frag_size) {
> + addr = skb_frag_address(&sinfo->frags[i]);
> + size = frag_size;
> + break;
> + }
> + offset -= frag_size;
> + }
> +
> +out:
> + if (offset + len < size)
> + return addr + offset; /* fast path - no need to copy */
> +
> + if (!buf) /* no copy to the bounce buffer */
> + return NULL;
> +
> + /* slow path - we need to copy data into the bounce buffer */
> + bpf_xdp_copy_buf(xdp, offset, len, buf, false);
> + return buf;
> +}
> +
> +BPF_CALL_4(bpf_xdp_load_bytes, struct xdp_buff *, xdp, u32, offset,
> + void *, buf, u32, len)
> +{
> + void *ptr;
> +
> + ptr = bpf_xdp_pointer(xdp, offset, len, buf);
> + if (ptr == ERR_PTR(-EINVAL))
> + return -EINVAL;
nit + same below in *_store_bytes(): IS_ERR(ptr) return PTR_ERR(ptr); ? (Or
should we just return -EFAULT to make it analog to bpf_skb_{load,store}_bytes()?
Either is okay, imho.)
> + if (ptr != buf)
> + memcpy(buf, ptr, len);
> +
> + return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_xdp_load_bytes_proto = {
> + .func = bpf_xdp_load_bytes,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_ANYTHING,
> + .arg3_type = ARG_PTR_TO_MEM,
ARG_PTR_TO_UNINIT_MEM, or do you need the dst buffer to be initialized?
> + .arg4_type = ARG_CONST_SIZE_OR_ZERO,
ARG_CONST_SIZE
> +};
> +
> +BPF_CALL_4(bpf_xdp_store_bytes, struct xdp_buff *, xdp, u32, offset,
> + void *, buf, u32, len)
> +{
> + void *ptr;
> +
> + ptr = bpf_xdp_pointer(xdp, offset, len, NULL);
> + if (ptr == ERR_PTR(-EINVAL))
> + return -EINVAL;
> +
> + if (!ptr)
> + bpf_xdp_copy_buf(xdp, offset, len, buf, true);
> + else
> + memcpy(ptr, buf, len);
> +
> + return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_xdp_store_bytes_proto = {
> + .func = bpf_xdp_store_bytes,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_ANYTHING,
> + .arg3_type = ARG_PTR_TO_MEM,
> + .arg4_type = ARG_CONST_SIZE_OR_ZERO,
ARG_CONST_SIZE, or do you have a use case for bpf_xdp_store_bytes(..., buf, 0)?
> +};
> +
> static int bpf_xdp_mb_increase_tail(struct xdp_buff *xdp, int offset)
> {
> struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> @@ -7619,6 +7749,10 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_xdp_adjust_tail_proto;
> case BPF_FUNC_xdp_get_buff_len:
> return &bpf_xdp_get_buff_len_proto;
> + case BPF_FUNC_xdp_load_bytes:
> + return &bpf_xdp_load_bytes_proto;
> + case BPF_FUNC_xdp_store_bytes:
> + return &bpf_xdp_store_bytes_proto;
> case BPF_FUNC_fib_lookup:
> return &bpf_xdp_fib_lookup_proto;
> case BPF_FUNC_check_mtu:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 1cb992ec0cc8..dad1d8c3a4c1 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -4920,6 +4920,22 @@ union bpf_attr {
> * Get the total size of a given xdp buff (linear and paged area)
> * Return
> * The total size of a given xdp buffer.
> + *
> + * long bpf_xdp_load_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
> + * Description
> + * This helper is provided as an easy way to load data from a
> + * xdp buffer. It can be used to load *len* bytes from *offset* from
> + * the frame associated to *xdp_md*, into the buffer pointed by
> + * *buf*.
> + * Return
> + * 0 on success, or a negative error in case of failure.
> + *
> + * long bpf_xdp_store_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
> + * Description
> + * Store *len* bytes from buffer *buf* into the frame
> + * associated to *xdp_md*, at *offset*.
> + * Return
> + * 0 on success, or a negative error in case of failure.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5101,6 +5117,8 @@ union bpf_attr {
> FN(get_branch_snapshot), \
> FN(trace_vprintk), \
> FN(xdp_get_buff_len), \
> + FN(xdp_load_bytes), \
> + FN(xdp_store_bytes), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>
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