• Alexander Lobakin's avatar
    bpf, test_run: fix &xdp_frame misplacement for LIVE_FRAMES · 294635a8
    Alexander Lobakin authored
    &xdp_buff and &xdp_frame are bound in a way that
    
    xdp_buff->data_hard_start == xdp_frame
    
    It's always the case and e.g. xdp_convert_buff_to_frame() relies on
    this.
    IOW, the following:
    
    	for (u32 i = 0; i < 0xdead; i++) {
    		xdpf = xdp_convert_buff_to_frame(&xdp);
    		xdp_convert_frame_to_buff(xdpf, &xdp);
    	}
    
    shouldn't ever modify @xdpf's contents or the pointer itself.
    However, "live packet" code wrongly treats &xdp_frame as part of its
    context placed *before* the data_hard_start. With such flow,
    data_hard_start is sizeof(*xdpf) off to the right and no longer points
    to the XDP frame.
    
    Instead of replacing `sizeof(ctx)` with `offsetof(ctx, xdpf)` in several
    places and praying that there are no more miscalcs left somewhere in the
    code, unionize ::frm with ::data in a flex array, so that both starts
    pointing to the actual data_hard_start and the XDP frame actually starts
    being a part of it, i.e. a part of the headroom, not the context.
    A nice side effect is that the maximum frame size for this mode gets
    increased by 40 bytes, as xdp_buff::frame_sz includes everything from
    data_hard_start (-> includes xdpf already) to the end of XDP/skb shared
    info.
    Also update %MAX_PKT_SIZE accordingly in the selftests code. Leave it
    hardcoded for 64 bit && 4k pages, it can be made more flexible later on.
    
    Minor: align `&head->data` with how `head->frm` is assigned for
    consistency.
    Minor #2: rename 'frm' to 'frame' in &xdp_page_head while at it for
    clarity.
    
    (was found while testing XDP traffic generator on ice, which calls
     xdp_convert_frame_to_buff() for each XDP frame)
    
    Fixes: b530e9e1 ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN")
    Acked-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
    Signed-off-by: default avatarAlexander Lobakin <aleksander.lobakin@intel.com>
    Link: https://lore.kernel.org/r/20230224163607.2994755-1-aleksander.lobakin@intel.comSigned-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
    294635a8
test_run.c 40.2 KB