From: Jesper Dangaard Brouer <hawk@xxxxxxxxxx> Date: Tue, 28 Nov 2023 12:30:41 +0100 > > > On 11/28/23 11:33, Larysa Zaremba wrote: >> On Tue, Nov 28, 2023 at 11:26:59AM +0100, Jesper Dangaard Brouer wrote: >>> >>> >>> On 11/27/23 19:32, Larysa Zaremba wrote: >>>> Currently, there is no reason for data_meta to be limited to 32 bytes. >>>> Loosen this limitation and make maximum meta size 252. >>> >>> First I though you made a type here with 252 bytes, but then I >>> remembered >>> the 4 byte alignment. >>> I think commit message should elaborate on why 252 bytes. >>> >> >> You are right, will do. >> > > I'm looking at the code to see if metadata can be extended into area > used by xdp_frame, such that a BPF-prog get direct memory access to this > (which should not be allowed). The bpf_xdp_adjust_meta() helper does > handle this (as you/Olek also mentioned in commit msg). A driver could > set data_meta such that they overlap, but I guess we will categorize > this as a driver bug. > > The XDP headroom have evolved to become dynamic (commonly 192 or 256 > bytes). Thus, we cannot statically reduce metalen with sizeof(struct > xdp_frame). The maximum meta size 252, could be achieved (and valid) if > a driver chooses to have more XDP headroom e.g. 288 bytes. So, I guess > it is correct to say maximum valid meta size is 252 bytes, but can be > limited and reduced further by drivers chosen XDP headroom and memory > reserved by struct xdp_frame (limited in bpf_xdp_adjust_meta). Drivers which don't provide 256 bytes of headroom for XDP are pathological :p Either way, as Larysa and you mentioned, the actual available headroom is checked with adjust_meta(), so here we just make sure its size fits into u8 meta_len of &skb_shared_info. > > > >>>> >>>> Also, modify the selftest, so test_xdp_context_error does not complain >>>> about the unexpected success. >>>> >>>> v2->v3: >>>> * Fix main patch author >>>> * Add selftests path >>>> >>>> v1->v2: >>>> * replace 'typeof(metalen)' with the actual type >>>> >>>> Aleksander Lobakin (1): >>>> net, xdp: allow metadata > 32 >>>> >>>> Larysa Zaremba (1): >>>> selftests/bpf: increase invalid metadata size >>>> >>>> include/linux/skbuff.h | 13 >>>> ++++++++----- >>>> include/net/xdp.h | 7 ++++++- >>>> .../selftests/bpf/prog_tests/xdp_context_test_run.c | 4 ++-- >>>> 3 files changed, 16 insertions(+), 8 deletions(-) >>>> Thanks, Olek
