[PATCH net v4 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.

Move the common logic to i40e_clean_programming_status and update both
i40e_clean_rx_irq and i40e_clean_rx_irq_zc accordingly.

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   | 59 +++++++++++--------
 .../ethernet/intel/i40e/i40e_txrx_common.h    |  5 +-
 drivers/net/ethernet/intel/i40e/i40e_xsk.c    | 14 ++---
 3 files changed, 42 insertions(+), 36 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index cc0b9efc2637..fe2190f4b9bc 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -1386,22 +1386,36 @@ static void i40e_reuse_rx_page(struct i40e_ring *rx_ring,
  * @rx_ring: the rx ring that has this descriptor
  * @qword0_raw: qword0
  * @qword1: qword1 representing status_error_len in CPU ordering
+ * @next_to_process: pointer to next_to_process index
+ * @next_to_clean: pointer to next_to_clean index
  *
  * Flow director should handle FD_FILTER_STATUS to check its filter programming
  * status being successful or not and take actions accordingly. FCoE should
  * handle its context/filter programming/invalidation status and take actions.
  *
- * Returns an i40e_rx_buffer to reuse if the cleanup occurred, otherwise NULL.
+ * Returns false if what is passed is not a status descriptor.
  **/
-void i40e_clean_programming_status(struct i40e_ring *rx_ring, u64 qword0_raw,
-				   u64 qword1)
+bool i40e_clean_programming_status(struct i40e_ring *rx_ring, u64 qword0_raw,
+				   u64 qword1, u16 *next_to_process,
+				   u16 *next_to_clean)
 {
+	u16 ntp = *next_to_process;
 	u8 id;
 
+	if (!i40e_rx_is_programming_status(qword1))
+		return false;
+
 	id = FIELD_GET(I40E_RX_PROG_STATUS_DESC_QW1_PROGID_MASK, qword1);
 
 	if (id == I40E_RX_PROG_STATUS_DESC_FD_FILTER_STATUS)
 		i40e_fd_handle_status(rx_ring, qword0_raw, qword1, id);
+
+	if (++*next_to_process == rx_ring->count)
+		*next_to_process = 0;
+	if (ntp == *next_to_clean)
+		*next_to_clean = *next_to_process;
+
+	return true;
 }
 
 /**
@@ -1971,19 +1985,18 @@ static void i40e_rx_buffer_flip(struct i40e_rx_buffer *rx_buffer,
 }
 
 /**
- * i40e_get_rx_buffer - Fetch Rx buffer and synchronize data for use
+ * i40e_prepare_rx_buffer - Synchronize the buffer for use by the CPU
  * @rx_ring: rx descriptor ring to transact packets on
+ * @rx_buffer: the rx buffer
  * @size: size of buffer to add to skb
  *
- * This function will pull an Rx buffer from the ring and synchronize it
- * for use by the CPU.
+ * This function will synchronize the given buffer for use by the CPU.
  */
-static struct i40e_rx_buffer *i40e_get_rx_buffer(struct i40e_ring *rx_ring,
-						 const unsigned int size)
+static struct i40e_rx_buffer *
+i40e_prepare_rx_buffer(struct i40e_ring *rx_ring,
+		       struct i40e_rx_buffer *rx_buffer,
+		       const unsigned int size)
 {
-	struct i40e_rx_buffer *rx_buffer;
-
-	rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_process);
 	rx_buffer->page_count =
 #if (PAGE_SIZE < 8192)
 		page_count(rx_buffer->page);
@@ -2450,6 +2463,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 
 	while (likely(total_rx_packets < (unsigned int)budget)) {
 		u16 ntp = rx_ring->next_to_process;
+		u16 ntc = rx_ring->next_to_clean;
 		struct i40e_rx_buffer *rx_buffer;
 		union i40e_rx_desc *rx_desc;
 		struct sk_buff *skb;
@@ -2480,21 +2494,15 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 		 */
 		dma_rmb();
 
-		if (i40e_rx_is_programming_status(qword)) {
-			i40e_clean_programming_status(rx_ring,
-						      rx_desc->raw.qword[0],
-						      qword);
-			rx_buffer = i40e_rx_bi(rx_ring, ntp);
-			i40e_inc_ntp(rx_ring);
+		rx_buffer = i40e_rx_bi(rx_ring, ntp);
+
+		if (i40e_clean_programming_status(rx_ring,
+						  rx_desc->raw.qword[0], qword,
+						  &rx_ring->next_to_process,
+						  &rx_ring->next_to_clean)) {
 			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;
+			if (ntc != rx_ring->next_to_clean)
 				cleaned_count++;
-			}
 			continue;
 		}
 
@@ -2503,8 +2511,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 			break;
 
 		i40e_trace(clean_rx_irq, rx_ring, rx_desc, xdp);
-		/* retrieve a buffer from the ring */
-		rx_buffer = i40e_get_rx_buffer(rx_ring, size);
+		i40e_prepare_rx_buffer(rx_ring, rx_buffer, size);
 
 		neop = i40e_is_non_eop(rx_ring, rx_desc);
 		i40e_inc_ntp(rx_ring);
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
index e26807fd2123..21d9ed878bf0 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
@@ -7,8 +7,9 @@
 #include "i40e.h"
 
 int i40e_xmit_xdp_tx_ring(struct xdp_buff *xdp, struct i40e_ring *xdp_ring);
-void i40e_clean_programming_status(struct i40e_ring *rx_ring, u64 qword0_raw,
-				   u64 qword1);
+bool i40e_clean_programming_status(struct i40e_ring *rx_ring, u64 qword0_raw,
+				   u64 qword1, u16 *next_to_clean,
+				   u16 *next_to_process);
 void i40e_process_skb_fields(struct i40e_ring *rx_ring,
 			     union i40e_rx_desc *rx_desc, struct sk_buff *skb);
 void i40e_xdp_ring_update_tail(struct i40e_ring *xdp_ring);
diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
index 9f47388eaba5..f8accc266c2c 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
@@ -440,14 +440,13 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 		 */
 		dma_rmb();
 
-		if (i40e_rx_is_programming_status(qword)) {
-			i40e_clean_programming_status(rx_ring,
-						      rx_desc->raw.qword[0],
-						      qword);
-			bi = *i40e_rx_bi(rx_ring, next_to_process);
+		bi = *i40e_rx_bi(rx_ring, next_to_process);
+
+		if (i40e_clean_programming_status(rx_ring,
+						  rx_desc->raw.qword[0],
+						  qword, &next_to_process,
+						  &next_to_clean)) {
 			xsk_buff_free(bi);
-			if (++next_to_process == count)
-				next_to_process = 0;
 			continue;
 		}
 
@@ -455,7 +454,6 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 		if (!size)
 			break;
 
-		bi = *i40e_rx_bi(rx_ring, next_to_process);
 		xsk_buff_set_size(bi, size);
 		xsk_buff_dma_sync_for_cpu(bi);
 
-- 
2.43.0