| Message ID | 20231127183216.269958-1-larysa.zaremba@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Allow data_meta size > 32 | expand |
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. > > 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(-) >
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. > > > > 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(-) > >
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). >>> >>> 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(-) >>>
From: Jesper Dangaard Brouer <hawk@kernel.org> 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