netdev - [PATCH] net: stmmac: add explicit check and error on invalid PTP clock rate

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Message-Id: <20250523-stmmac_tstamp_div-v1-1-bca8a5a3a477@bootlin.com>
Date: Fri, 23 May 2025 13:46:32 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Alexandre Torgue <alexandre.torgue@...s.st.com>, 
 Jose Abreu <joabreu@...opsys.com>, Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Maxime Coquelin <mcoquelin.stm32@...il.com>, 
 Richard Cochran <richardcochran@...il.com>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Maxime Chevallier <maxime.chevallier@...tlin.com>, netdev@...r.kernel.org, 
 linux-stm32@...md-mailman.stormreply.com, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Alexis Lothoré <alexis.lothore@...tlin.com>
Subject: [PATCH] net: stmmac: add explicit check and error on invalid PTP
 clock rate

While some platforms implementing dwmac open-code the clk_ptp_rate
value, some others dynamically retrieve the value at runtime. If the
retrieved value happens to be 0 for any reason, it will eventually
propagate up to PTP initialization when bringing up the interface,
leading to a divide by 0:

 Division by zero in kernel.
 CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.30-00001-g48313bd5768a #22
 Hardware name: STM32 (Device Tree Support)
 Call trace:
  unwind_backtrace from show_stack+0x18/0x1c
  show_stack from dump_stack_lvl+0x6c/0x8c
  dump_stack_lvl from Ldiv0_64+0x8/0x18
  Ldiv0_64 from stmmac_init_tstamp_counter+0x190/0x1a4
  stmmac_init_tstamp_counter from stmmac_hw_setup+0xc1c/0x111c
  stmmac_hw_setup from __stmmac_open+0x18c/0x434
  __stmmac_open from stmmac_open+0x3c/0xbc
  stmmac_open from __dev_open+0xf4/0x1ac
  __dev_open from __dev_change_flags+0x1cc/0x224
  __dev_change_flags from dev_change_flags+0x24/0x60
  dev_change_flags from ip_auto_config+0x2e8/0x11a0
  ip_auto_config from do_one_initcall+0x84/0x33c
  do_one_initcall from kernel_init_freeable+0x1b8/0x214
  kernel_init_freeable from kernel_init+0x24/0x140
  kernel_init from ret_from_fork+0x14/0x28
 Exception stack(0xe0815fb0 to 0xe0815ff8)

Prevent this division by 0 by adding an explicit check and error log
about the actual issue.

Signed-off-by: Alexis Lothoré <alexis.lothore@...tlin.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 918d7f2e8ba992208d7d6521a1e9dba01086058f..f68e3ece919cc88d0bf199a394bc7e44b5dee095 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -835,6 +835,11 @@ int stmmac_init_tstamp_counter(struct stmmac_priv *priv, u32 systime_flags)
 	if (!(priv->dma_cap.time_stamp || priv->dma_cap.atime_stamp))
 		return -EOPNOTSUPP;

+	if (!priv->plat->clk_ptp_rate) {
+		netdev_err(priv->dev, "Invalid PTP clock rate");
+		return -EINVAL;
+	}
+
 	stmmac_config_hw_tstamping(priv, priv->ptpaddr, systime_flags);
 	priv->systime_flags = systime_flags;

---
base-commit: e0e2f78243385e7188a57fcfceb6a19f723f1dff
change-id: 20250522-stmmac_tstamp_div-f55112f06029

Best regards,
-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com