net: enetc: fix race condition in VF MAC address configuration

Sashiko reported a potential race condition between the VF message
handler and administrative VF MAC configuration from the host [1].

The VF message handler (enetc_msg_pf_set_vf_primary_mac_addr) runs
asynchronously in a workqueue context and accesses vf_state->flags
without any locking. Concurrently, the host can administratively
change the VF MAC address via enetc_pf_set_vf_mac(), which executes
under RTNL lock and modifies both vf_state->flags and hardware
registers.

This creates two race windows:

1) TOCTOU race on vf_state->flags: The check of ENETC_VF_FLAG_PF_SET_MAC
   and subsequent MAC programming are not atomic, allowing the flag state
   to change between check and use.

2) Torn MAC address writes: Hardware MAC programming requires multiple
   non-atomic register writes (__raw_writel for lower 32 bits and
   __raw_writew for upper 16 bits). Concurrent updates from VF mailbox
   and PF admin paths can interleave these operations, resulting in a
   corrupted MAC address being programmed into the hardware.

Fix by introducing a per-VF mutex to serialize access to vf_state and
hardware MAC register updates. Both enetc_pf_set_vf_mac() and
enetc_msg_pf_set_vf_primary_mac_addr() now acquire this lock before
accessing vf_state->flags or programming the MAC address, ensuring
atomic read-modify-write sequences and preventing register write
interleaving.

Link: https://sashiko.dev/#/patchset/20260511080805.2052495-1-wei.fang%40nxp.com #1
Fixes: beb74ac878 ("enetc: Add vf to pf messaging support")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Link: https://patch.msgid.link/20260520064421.91569-6-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/enetc/enetc_pf.c

@@ -252,8 +252,12 @@ static int enetc_pf_set_vf_mac(struct net_device *ndev, int vf, u8 *mac)
 		return -EADDRNOTAVAIL;
 
 	vf_state = &pf->vf_state[vf];
+
+	mutex_lock(&vf_state->lock);
 	vf_state->flags |= ENETC_VF_FLAG_PF_SET_MAC;
 	enetc_pf_set_primary_mac_addr(&priv->si->hw, vf + 1, mac);
+	mutex_unlock(&vf_state->lock);
+
 	return 0;
 }
 
@@ -496,7 +500,9 @@ static u16 enetc_msg_pf_set_vf_primary_mac_addr(struct enetc_pf *pf,
 		return ENETC_MSG_CMD_STATUS_FAIL;
 	}
 
+	mutex_lock(&vf_state->lock);
 	if (vf_state->flags & ENETC_VF_FLAG_PF_SET_MAC) {
+		mutex_unlock(&vf_state->lock);
 		dev_err_ratelimited(dev,
 				    "VF%d attempted to override PF set MAC\n",
 				    vf_id);
@@ -504,6 +510,7 @@ static u16 enetc_msg_pf_set_vf_primary_mac_addr(struct enetc_pf *pf,
 	}
 
 	enetc_pf_set_primary_mac_addr(&pf->si->hw, vf_id + 1, addr);
+	mutex_unlock(&vf_state->lock);
 
 	return ENETC_MSG_CMD_STATUS_OK;
 }
@@ -989,6 +996,9 @@ static int enetc_pf_probe(struct pci_dev *pdev,
 			err = -ENOMEM;
 			goto err_alloc_vf_state;
 		}
+
+		for (int i = 0; i < pf->total_vfs; i++)
+			mutex_init(&pf->vf_state[i].lock);
 	}
 
 	err = enetc_setup_mac_addresses(node, pf);

drivers/net/ethernet/freescale/enetc/enetc_pf.h

@@ -14,6 +14,7 @@ enum enetc_vf_flags {
 };
 
 struct enetc_vf_state {
+	struct mutex lock; /* Prevent concurrent access */
 	enum enetc_vf_flags flags;
 };