> From: Jason Xing <[email protected]> > Sent: 22 October 2025 08:41 > On Wed, Oct 22, 2025 at 1:33 AM Alessandro Decina > <[email protected]> wrote: > > > > Whenever a status descriptor is received, i40e processes and skips over > > it, correctly updating next_to_process but forgetting to update > > next_to_clean. In the next iteration this accidentally causes the > > creation of an invalid multi-buffer xdp_buff where the first fragment > > is the status descriptor. > > > > If then a skb is constructed from such an invalid buffer - because the > > eBPF program returns XDP_PASS - a panic occurs: > > > > [ 5866.367317] BUG: unable to handle page fault for address: > ffd31c37eab1c980 > > [ 5866.375050] #PF: supervisor read access in kernel mode > > [ 5866.380825] #PF: error_code(0x0000) - not-present page > > [ 5866.386602] PGD 0 > > [ 5866.388867] Oops: Oops: 0000 [#1] SMP NOPTI > > [ 5866.393575] CPU: 34 UID: 0 PID: 0 Comm: swapper/34 Not tainted > 6.17.0-custom #1 PREEMPT(voluntary) > > [ 5866.403740] Hardware name: Supermicro AS -2115GT-HNTR/H13SST-G, > BIOS 3.2 03/20/2025 > > [ 5866.412339] RIP: 0010:memcpy+0x8/0x10 > > [ 5866.416454] Code: cc cc 90 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc > > 90 90 > 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 90 48 89 f8 48 89 d1 <f3> a4 > e9 fc 26 c0 fe 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 > > [ 5866.437538] RSP: 0018:ff428d9ec0bb0ca8 EFLAGS: 00010286 > > [ 5866.443415] RAX: ff2dd26dbd8f0000 RBX: ff2dd265ad161400 RCX: > 00000000000004e1 > > [ 5866.451435] RDX: 00000000000004e1 RSI: ffd31c37eab1c980 RDI: > ff2dd26dbd8f0000 > > [ 5866.459454] RBP: ff428d9ec0bb0d40 R08: 0000000000000000 R09: > 0000000000000000 > > [ 5866.467470] R10: 0000000000000000 R11: 0000000000000000 R12: > ff428d9eec726ef8 > > [ 5866.475490] R13: ff2dd26dbd8f0000 R14: ff2dd265ca2f9fc0 R15: > ff2dd26548548b80 > > [ 5866.483509] FS: 0000000000000000(0000) > GS:ff2dd2c363592000(0000) knlGS:0000000000000000 > > [ 5866.492600] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 5866.499060] CR2: ffd31c37eab1c980 CR3: 0000000178d7b040 CR4: > 0000000000f71ef0 > > [ 5866.507079] PKRU: 55555554 > > [ 5866.510125] Call Trace: > > [ 5866.512867] <IRQ> > > [ 5866.515132] ? i40e_clean_rx_irq_zc+0xc50/0xe60 [i40e] > > [ 5866.520921] i40e_napi_poll+0x2d8/0x1890 [i40e] > > [ 5866.526022] ? srso_alias_return_thunk+0x5/0xfbef5 > > [ 5866.531408] ? raise_softirq+0x24/0x70 > > [ 5866.535623] ? srso_alias_return_thunk+0x5/0xfbef5 > > [ 5866.541011] ? srso_alias_return_thunk+0x5/0xfbef5 > > [ 5866.546397] ? rcu_sched_clock_irq+0x225/0x1800 > > [ 5866.551493] __napi_poll+0x30/0x230 > > [ 5866.555423] net_rx_action+0x20b/0x3f0 > > [ 5866.559643] handle_softirqs+0xe4/0x340 > > [ 5866.563962] __irq_exit_rcu+0x10e/0x130 > > [ 5866.568283] irq_exit_rcu+0xe/0x20 > > [ 5866.572110] common_interrupt+0xb6/0xe0 > > [ 5866.576425] </IRQ> > > [ 5866.578791] <TASK> > > > > Advance next_to_clean to ensure invalid xdp_buff(s) aren't created. > > > > Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support") > > Signed-off-by: Alessandro Decina <[email protected]> > > --- > > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c > b/drivers/net/ethernet/intel/i40e/i40e_xsk.c > > index 9f47388eaba5..dbc19083bbb7 100644 > > --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c > > +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c > > @@ -441,13 +441,18 @@ int i40e_clean_rx_irq_zc(struct i40e_ring > *rx_ring, int budget) > > dma_rmb(); > > > > if (i40e_rx_is_programming_status(qword)) { > > + u16 ntp; > > + > > i40e_clean_programming_status(rx_ring, > > rx_desc->raw.qword[0], > > qword); > > bi = *i40e_rx_bi(rx_ring, next_to_process); > > xsk_buff_free(bi); > > - if (++next_to_process == count) > > + ntp = next_to_process++; > > + if (next_to_process == count) > > next_to_process = 0; > > + if (next_to_clean == ntp) > > + next_to_clean = next_to_process; > > continue; > > } > > > > -- > > 2.43.0 > > > > > > I'm copying your reply from v1 as shown below so that we can continue > with the discussion :) > > > It really depends on whether a status descriptor can be received in the > > middle of multi-buffer packet. Based on the existing code, I assumed it > > can. Therefore, consider this case: > > > > [valid_1st_packet][status_descriptor][valid_2nd_packet] > > > > In this case you want to skip status_descriptor but keep the existing > > logic that leads to: > > > > first = next_to_clean = valid_1st_packet > > > > so then you can go and add valid_2nd_packet as a fragment to the first. > > Sorry, honestly, I still don't follow you. > > Looking at the case you provided, I think @first always pointing to > valid_1st_packet is valid which does not bring any trouble. You mean > the case is what you're trying to handle? > > You patch updates next_to_clean that is only used at the very > beginning, so it will not affect @first. Imaging the following case: > > [status_descriptor][valid_1st_packet][valid_2nd_packet] > > Even if the next_to_clean is updated, the @first still points to > [status_descriptor] that is invalid and that will later cause the > panic when constructing the skb. > > I'm afraid that we're not on the same page. Let me confirm that it is > @first that points to the status descriptor that causes the panic, > right? Could you share with us the exact case just like you did as > above. Thank you. > > Thanks, > Jason
I believe the issue is not that status_descriptor is getting into multi-buffer packet but not updating next_to_clean results in I40E_DESC_UNUSED() to return incorrect values. A similar issue was reported and fixed on the non-ZC path: https://lore.kernel.org/netdev/[email protected]/ Thanks, Tirthendu
