[PATCH v3 0/2] net: stmmac: prevent div by 0

[PATCH v3 0/2] net: stmmac: prevent div by 0

[Alexis Lothoré]

Hello,
this small series aims to fix a small splat I am observing on a STM32MP157
platform at boot (see commit 1) due to a division by 0. This new
revision add the same check in another code path possibly affected by
the same issue, as discussed in v2.

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
---
Changes in v3:
- remove now duplicate check
- add ptp_rate check in est_configure
- Link to v2: https://lore.kernel.org/r/20250527-stmmac_tstamp_div-v2-1-663251b3b542@bootlin.com

Changes in v2:
- Add Fixes tag
- Reword commit message to clarify the triggering cause of the issue
- Link to v1: https://lore.kernel.org/r/20250523-stmmac_tstamp_div-v1-1-bca8a5a3a477@bootlin.com

---
Alexis Lothoré (2):
      net: stmmac: make sure that ptp_rate is not 0 before configuring timestamping
      net: stmmac: make sure that ptp_rate is not 0 before configuring EST

 drivers/net/ethernet/stmicro/stmmac/stmmac_est.c  | 5 +++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c  | 2 +-
 3 files changed, 11 insertions(+), 1 deletion(-)
---
base-commit: e0e2f78243385e7188a57fcfceb6a19f723f1dff
change-id: 20250522-stmmac_tstamp_div-f55112f06029

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

[PATCH v3 1/2] net: stmmac: make sure that ptp_rate is not 0 before configuring timestamping

[Alexis Lothoré]

The stmmac platform drivers that do not open-code the clk_ptp_rate value
after having retrieved the default one from the device-tree can end up
with 0 in clk_ptp_rate (as clk_get_rate can return 0). 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. While at it, remove the same check from
stmmac_ptp_register, which then becomes duplicate

Fixes: 19d857c9038e ("stmmac: Fix calculations for ptp counters when clock input = 50Mhz.")
Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
---
Changes in v3:
- remove now-duplicate check
- reword commit message
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c  | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

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;
 
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
index a6b1de9a251dd4fdc083e59717b57ff3b94cefb4..5c85040a1b937ecd1deb701ceaca47df5f3834f3 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
@@ -303,7 +303,7 @@ void stmmac_ptp_register(struct stmmac_priv *priv)
 
 	/* Calculate the clock domain crossing (CDC) error if necessary */
 	priv->plat->cdc_error_adj = 0;
-	if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate)
+	if (priv->plat->has_gmac4)
 		priv->plat->cdc_error_adj = (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;
 
 	stmmac_ptp_clock_ops.n_per_out = priv->dma_cap.pps_out_num;

-- 
2.49.0

[PATCH v3 2/2] net: stmmac: make sure that ptp_rate is not 0 before configuring EST

[Alexis Lothoré]

If the ptp_rate recorded earlier in the driver happens to be 0, this
bogus value will propagate up to EST configuration, where it will
trigger a division by 0.

Prevent this division by 0 by adding the corresponding check and error
code.

Suggested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Fixes: 8572aec3d0dc ("net: stmmac: Add basic EST support for XGMAC")
---
Changes in v3:
- new patch
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_est.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_est.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_est.c
index c9693f77e1f61fe5c92f95f5e544371445626c4d..ac6f2e3a3fcd2f9ae21913845282ff015cd2f7ec 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_est.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_est.c
@@ -32,6 +32,11 @@ static int est_configure(struct stmmac_priv *priv, struct stmmac_est *cfg,
 	int i, ret = 0;
 	u32 ctrl;
 
+	if (!ptp_rate) {
+		netdev_warn(priv->dev, "Invalid PTP rate");
+		return -EINVAL;
+	}
+
 	ret |= est_write(est_addr, EST_BTR_LOW, cfg->btr[0], false);
 	ret |= est_write(est_addr, EST_BTR_HIGH, cfg->btr[1], false);
 	ret |= est_write(est_addr, EST_TER, cfg->ter, false);

-- 
2.49.0

Re: [PATCH v3 1/2] net: stmmac: make sure that ptp_rate is not 0 before configuring timestamping

[Alexis Lothoré]

On Wed May 28, 2025 at 10:29 AM CEST, Alexis Lothoré wrote:
> The stmmac platform drivers that do not open-code the clk_ptp_rate value
> after having retrieved the default one from the device-tree can end up
> with 0 in clk_ptp_rate (as clk_get_rate can return 0). 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. While at it, remove the same check from
> stmmac_ptp_register, which then becomes duplicate
>
> Fixes: 19d857c9038e ("stmmac: Fix calculations for ptp counters when clock input = 50Mhz.")
> Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>

I realize that I forgot to collect Yanteng's and Maxime's RB on this patch,
and I guess they remain relevant despite the second new patch, my bad. I'll
remember to add them if this needs a new revision.

Alexis




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

Re: [PATCH v3 0/2] net: stmmac: prevent div by 0

[Jakub Kicinski]

On Wed, 28 May 2025 10:29:49 +0200 Alexis Lothoré wrote:
> Hello,
> this small series aims to fix a small splat I am observing on a STM32MP157
> platform at boot (see commit 1) due to a division by 0. This new
> revision add the same check in another code path possibly affected by
> the same issue, as discussed in v2.

v3 doesnt apply cleanly. Could you rebase on latest net and repost?