[PATCH net v3 1/1] i40e: xsk: advance next_to_clean on status descriptors

[Alessandro Decina <alessandro.d@gmail.com>]

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.

Rename i40e_inc_ntp to i40e_inc_ntp_ntc. Make it take an optional
pointer to next_to_clean so it's harder for callers to accidentally
forget to advance it.

Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
Signed-off-by: Alessandro Decina <alessandro.d@gmail.com>
---
 drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 33 ++++++++++++-------
 .../ethernet/intel/i40e/i40e_txrx_common.h    |  2 ++
 drivers/net/ethernet/intel/i40e/i40e_xsk.c    | 17 ++++++----
 3 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index cc0b9efc2637..d3dae895a058 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -2359,15 +2359,24 @@ void i40e_finalize_xdp_rx(struct i40e_ring *rx_ring, unsigned int xdp_res)
 }
 
 /**
- * i40e_inc_ntp: Advance the next_to_process index
+ * i40e_inc_ntp_ntc: Advance the next_to_process and next_to_clean indexes
  * @rx_ring: Rx ring
+ * @next_to_process: Pointer to next_to_process
+ * @next_to_clean: Pointer to next_to_clean or NULL
+ *
+ * This function advances the next_to_process index. If next_to_clean is not
+ * NULL, it is advanced as well.
  **/
-static void i40e_inc_ntp(struct i40e_ring *rx_ring)
+void i40e_inc_ntp_ntc(struct i40e_ring *rx_ring, u16 *next_to_process,
+		      u16 *next_to_clean)
 {
-	u32 ntp = rx_ring->next_to_process + 1;
+	u16 ntp = *next_to_process + 1;
 
 	ntp = (ntp < rx_ring->count) ? ntp : 0;
-	rx_ring->next_to_process = ntp;
+	*next_to_process = ntp;
+	if (next_to_clean)
+		*next_to_clean = ntp;
+
 	prefetch(I40E_RX_DESC(rx_ring, ntp));
 }
 
@@ -2484,17 +2493,19 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 			i40e_clean_programming_status(rx_ring,
 						      rx_desc->raw.qword[0],
 						      qword);
+			bool eop;
+
 			rx_buffer = i40e_rx_bi(rx_ring, ntp);
-			i40e_inc_ntp(rx_ring);
-			i40e_reuse_rx_page(rx_ring, rx_buffer);
 			/* Update ntc and bump cleaned count if not in the
 			 * middle of mb packet.
 			 */
-			if (rx_ring->next_to_clean == ntp) {
-				rx_ring->next_to_clean =
-					rx_ring->next_to_process;
+			eop = rx_ring->next_to_process ==
+			      rx_ring->next_to_clean;
+			i40e_inc_ntp_ntc(rx_ring, &rx_ring->next_to_process,
+					 eop ? &rx_ring->next_to_clean : NULL);
+			if (eop)
 				cleaned_count++;
-			}
+			i40e_reuse_rx_page(rx_ring, rx_buffer);
 			continue;
 		}
 
@@ -2507,7 +2518,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 		rx_buffer = i40e_get_rx_buffer(rx_ring, size);
 
 		neop = i40e_is_non_eop(rx_ring, rx_desc);
-		i40e_inc_ntp(rx_ring);
+		i40e_inc_ntp_ntc(rx_ring, &rx_ring->next_to_process, NULL);
 
 		if (!xdp->data) {
 			unsigned char *hard_start;
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
index e26807fd2123..3d7e4b3404f0 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
@@ -17,6 +17,8 @@ void i40e_update_rx_stats(struct i40e_ring *rx_ring,
 			  unsigned int total_rx_packets);
 void i40e_finalize_xdp_rx(struct i40e_ring *rx_ring, unsigned int xdp_res);
 void i40e_release_rx_desc(struct i40e_ring *rx_ring, u32 val);
+void i40e_inc_ntp_ntc(struct i40e_ring *rx_ring, u16 *next_to_process,
+		      u16 *next_to_clean);
 
 #define I40E_XDP_PASS		0
 #define I40E_XDP_CONSUMED	BIT(0)
diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
index 9f47388eaba5..fdf72446ed67 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
@@ -410,7 +410,6 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 	u16 next_to_clean = rx_ring->next_to_clean;
 	unsigned int xdp_res, xdp_xmit = 0;
 	struct xdp_buff *first = NULL;
-	u32 count = rx_ring->count;
 	struct bpf_prog *xdp_prog;
 	u32 entries_to_alloc;
 	bool failure = false;
@@ -430,6 +429,7 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 		struct xdp_buff *bi;
 		unsigned int size;
 		u64 qword;
+		bool neop;
 
 		rx_desc = I40E_RX_DESC(rx_ring, next_to_process);
 		qword = le64_to_cpu(rx_desc->wb.qword1.status_error_len);
@@ -446,8 +446,10 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 						      qword);
 			bi = *i40e_rx_bi(rx_ring, next_to_process);
 			xsk_buff_free(bi);
-			if (++next_to_process == count)
-				next_to_process = 0;
+			i40e_inc_ntp_ntc(rx_ring, &next_to_process,
+					 next_to_process == next_to_clean ?
+						 &next_to_clean :
+						 NULL);
 			continue;
 		}
 
@@ -466,16 +468,17 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 			break;
 		}
 
-		if (++next_to_process == count)
-			next_to_process = 0;
+		neop = i40e_is_non_eop(rx_ring, rx_desc);
+		// advance next_to_process. on EOP, advance next_to_clean as well.
+		i40e_inc_ntp_ntc(rx_ring, &next_to_process,
+				 !neop ? &next_to_clean : NULL);
 
-		if (i40e_is_non_eop(rx_ring, rx_desc))
+		if (neop)
 			continue;
 
 		xdp_res = i40e_run_xdp_zc(rx_ring, first, xdp_prog);
 		i40e_handle_xdp_result_zc(rx_ring, first, rx_desc, &rx_packets,
 					  &rx_bytes, xdp_res, &failure);
-		next_to_clean = next_to_process;
 		if (failure)
 			break;
 		total_rx_packets += rx_packets;
-- 
2.43.0