Commit 23680bf5f8c6 for kernel

commit 23680bf5f8c69c923546b84a8e6c401bef8b88fe
Author: Pascal Kneuper <PKneuper@dspace.de>
Date:   Mon Aug 24 14:50:14 2026 +0200

    net: stmmac: restore NET_IP_ALIGN in the RX DMA offset

    Since the RX path was converted to zero-copy, the page pool page is handed
    to the stack directly as the skb head, and the offset the DMA engine writes
    at is what determines the alignment of the packet headers.

    Before the conversion the payload was copied into an skb obtained from
    napi_alloc_skb(), which reserves NET_SKB_PAD + NET_IP_ALIGN. The
    conversion moved the headroom into stmmac_rx_offset() but did not carry
    over NET_IP_ALIGN, so on architectures where NET_IP_ALIGN is 2 the IP
    header now lands misaligned:

      64 (NET_SKB_PAD) + 14 (ethernet) + 20 (IP) = 98

    Same for the XDP branch:

      256 (XDP_PACKET_HEADROOM) + 14 (ethernet) + 20 (IP) = 290

    On ARM32 this is fatal, because ldm and ldrd trap on unaligned addresses
    even when CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is set.

    Any received echo request panics the machine, e.g:

      Unhandled fault: alignment exception (0x001) at 0x81873062
      Internal error: : 1 [#1] SMP ARM
      Hardware name: Altera SOCFPGA Arria10
      PC is at icmp_echo+0x38/0xa8
      LR is at icmp_rcv+0x22c/0x370
      Call trace:
       icmp_echo from icmp_rcv+0x22c/0x370
       icmp_rcv from ip_protocol_deliver_rcu+0x2c/0x224
       ip_protocol_deliver_rcu from ip_local_deliver+0xc8/0x1a0
       ip_local_deliver from ip_sublist_rcv_finish+0x3c/0x50
       ip_sublist_rcv_finish from ip_list_rcv_finish+0x110/0x118
       ip_list_rcv_finish from ip_list_rcv+0xc8/0xdc
       ip_list_rcv from __netif_receive_skb_list_core+0x170/0x1c0
       ...
       napi_complete_done from stmmac_napi_poll_rx+0xcb0/0x1030
      Code: e24dd068 e59020a0 e28dc010 e0822001 (e8920003)
      Kernel panic - not syncing: Fatal exception in interrupt

    The faulting instruction is the ldm of *icmp_hdr(skb) in icmp_echo().

    Fix by adding NET_IP_ALIGN back to the RX offset, which restores the
    alignment the stack used to get.

    Note that commit a955318fe67e ("stmmac: align RX buffers") made a similar
    change in 2021 and was reverted by commit 12d125b4574b ("stmmac: Revert
    "stmmac: align RX buffers"") because it caused packet corruption. That
    patch raised the offset from 0 without adjusting the buffer size
    accounting, so the DMA engine could arguably write past the end of the RX
    buffers, though this was never root caused.
    Commit df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX
    path") since derives the page pool allocation from stmmac_rx_offset(), so
    the extra bytes are accounted for.

    Fixes: df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX path")
    Cc: Daniel Baldin <DBaldin@dspace.de>
    Signed-off-by: Pascal Kneuper <PKneuper@dspace.de>
    Link: https://patch.msgid.link/20260824125014.47862-1-PKneuper@dspace.de
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index bc6ba4be18b1..f2fc89176654 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1531,9 +1531,9 @@ static void stmmac_display_rings(struct stmmac_priv *priv,
 static unsigned int stmmac_rx_offset(struct stmmac_priv *priv)
 {
 	if (stmmac_xdp_is_enabled(priv))
-		return XDP_PACKET_HEADROOM;
+		return XDP_PACKET_HEADROOM + NET_IP_ALIGN;

-	return NET_SKB_PAD;
+	return NET_SKB_PAD + NET_IP_ALIGN;
 }

 static int stmmac_set_bfsize(int mtu)