lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Mon,  4 Jul 2022 14:26:10 +0200
From:   Marc Kleine-Budde <>
Cc:,,,, Thomas Kopp <>,, Marc Kleine-Budde <>
Subject: [PATCH net 12/15] can: mcp251xfd: mcp251xfd_regmap_crc_read(): update workaround broken CRC on TBC register

From: Thomas Kopp <>

The mcp251xfd compatible chips have an erratum ([1], [2]), where the
received CRC doesn't match the calculated CRC. In commit
c7eb923c3caf ("can: mcp251xfd: mcp251xfd_regmap_crc_read(): work
around broken CRC on TBC register") the following workaround was

- If a CRC read error on the TBC register is detected and the first
  byte is 0x00 or 0x80, the most significant bit of the first byte is
  flipped and the CRC is calculated again.
- If the CRC now matches, the _original_ data is passed to the reader.
  For now we assume transferred data was OK.

New investigations and simulations indicate that the CRC send by the
device is calculated on correct data, and the data is incorrectly
received by the SPI host controller.

Use flipped instead of original data and update workaround description
in mcp251xfd_regmap_crc_read().

[1] mcp2517fd: DS80000792C: "Incorrect CRC for certain READ_CRC commands"
[2] mcp2518fd: DS80000789C: "Incorrect CRC for certain READ_CRC commands"

Fixes: c7eb923c3caf ("can: mcp251xfd: mcp251xfd_regmap_crc_read(): work around broken CRC on TBC register")
Signed-off-by: Thomas Kopp <>
[mkl: split into 2 patches, update patch description and documentation]
Signed-off-by: Marc Kleine-Budde <>
 drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
index 211edd9ef0c9..92b7bc7f14b9 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-regmap.c
@@ -343,9 +343,8 @@ mcp251xfd_regmap_crc_read(void *context,
 		 * If the highest bit in the lowest byte is flipped
 		 * the transferred CRC matches the calculated one. We
-		 * assume for now the CRC calculation in the chip
-		 * works on wrong data and the transferred data is
-		 * correct.
+		 * assume for now the CRC operates on the correct
+		 * data.
 		if (reg == MCP251XFD_REG_TBC &&
 		    ((buf_rx->data[0] & 0xf8) == 0x0 ||
@@ -359,10 +358,8 @@ mcp251xfd_regmap_crc_read(void *context,
 			if (!err) {
 				/* If CRC is now correct, assume
-				 * transferred data was OK, flip bit
-				 * back to original value.
+				 * flipped data is OK.
-				buf_rx->data[0] ^= 0x80;
 				goto out;

Powered by blists - more mailing lists