Patch "stmmac: fix potential division by 0" has been added to the 4.19-stable tree

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This is a note to let you know that I've just added the patch titled

    stmmac: fix potential division by 0

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     stmmac-fix-potential-division-by-0.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 07e0195e932d5a74200ef76e0d8afab93fa645ab
Author: Piergiorgio Beruto <piergiorgio.beruto@xxxxxxxxx>
Date:   Sat Dec 10 23:37:22 2022 +0100

    stmmac: fix potential division by 0
    
    [ Upstream commit ede5a389852d3640a28e7187fb32b7f204380901 ]
    
    When the MAC is connected to a 10 Mb/s PHY and the PTP clock is derived
    from the MAC reference clock (default), the clk_ptp_rate becomes too
    small and the calculated sub second increment becomes 0 when computed by
    the stmmac_config_sub_second_increment() function within
    stmmac_init_tstamp_counter().
    
    Therefore, the subsequent div_u64 in stmmac_init_tstamp_counter()
    operation triggers a divide by 0 exception as shown below.
    
    [   95.062067] socfpga-dwmac ff700000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
    [   95.076440] socfpga-dwmac ff700000.ethernet eth0: PHY [stmmac-0:08] driver [NCN26000] (irq=49)
    [   95.095964] dwmac1000: Master AXI performs any burst length
    [   95.101588] socfpga-dwmac ff700000.ethernet eth0: No Safety Features support found
    [   95.109428] Division by zero in kernel.
    [   95.113447] CPU: 0 PID: 239 Comm: ifconfig Not tainted 6.1.0-rc7-centurion3-1.0.3.0-01574-gb624218205b7-dirty #77
    [   95.123686] Hardware name: Altera SOCFPGA
    [   95.127695]  unwind_backtrace from show_stack+0x10/0x14
    [   95.132938]  show_stack from dump_stack_lvl+0x40/0x4c
    [   95.137992]  dump_stack_lvl from Ldiv0+0x8/0x10
    [   95.142527]  Ldiv0 from __aeabi_uidivmod+0x8/0x18
    [   95.147232]  __aeabi_uidivmod from div_u64_rem+0x1c/0x40
    [   95.152552]  div_u64_rem from stmmac_init_tstamp_counter+0xd0/0x164
    [   95.158826]  stmmac_init_tstamp_counter from stmmac_hw_setup+0x430/0xf00
    [   95.165533]  stmmac_hw_setup from __stmmac_open+0x214/0x2d4
    [   95.171117]  __stmmac_open from stmmac_open+0x30/0x44
    [   95.176182]  stmmac_open from __dev_open+0x11c/0x134
    [   95.181172]  __dev_open from __dev_change_flags+0x168/0x17c
    [   95.186750]  __dev_change_flags from dev_change_flags+0x14/0x50
    [   95.192662]  dev_change_flags from devinet_ioctl+0x2b4/0x604
    [   95.198321]  devinet_ioctl from inet_ioctl+0x1ec/0x214
    [   95.203462]  inet_ioctl from sock_ioctl+0x14c/0x3c4
    [   95.208354]  sock_ioctl from vfs_ioctl+0x20/0x38
    [   95.212984]  vfs_ioctl from sys_ioctl+0x250/0x844
    [   95.217691]  sys_ioctl from ret_fast_syscall+0x0/0x4c
    [   95.222743] Exception stack(0xd0ee1fa8 to 0xd0ee1ff0)
    [   95.227790] 1fa0:                   00574c4f be9aeca4 00000003 00008914 be9aeca4 be9aec50
    [   95.235945] 1fc0: 00574c4f be9aeca4 0059f078 00000036 be9aee8c be9aef7a 00000015 00000000
    [   95.244096] 1fe0: 005a01f0 be9aec38 004d7484 b6e67d74
    
    Signed-off-by: Piergiorgio Beruto <piergiorgio.beruto@xxxxxxxxx>
    Fixes: 91a2559c1dc5 ("net: stmmac: Fix sub-second increment")
    Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
    Link: https://lore.kernel.org/r/de4c64ccac9084952c56a06a8171d738604c4770.1670678513.git.piergiorgio.beruto@xxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index 08a058e1bc75..541c0449f31c 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -53,7 +53,8 @@ static void config_sub_second_increment(void __iomem *ioaddr,
 	if (!(value & PTP_TCR_TSCTRLSSR))
 		data = (data * 1000) / 465;
 
-	data &= PTP_SSIR_SSINC_MASK;
+	if (data > PTP_SSIR_SSINC_MAX)
+		data = PTP_SSIR_SSINC_MAX;
 
 	reg_value = data;
 	if (gmac4)
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
index ecccf895fd7e..306ebf1a495e 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
@@ -66,7 +66,7 @@
 #define	PTP_TCR_TSENMACADDR	BIT(18)
 
 /* SSIR defines */
-#define	PTP_SSIR_SSINC_MASK		0xff
+#define	PTP_SSIR_SSINC_MAX		0xff
 #define	GMAC4_PTP_SSIR_SSINC_SHIFT	16
 
 #endif	/* __STMMAC_PTP_H__ */



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