linux-kernel - [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer

lists.openwall.net		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 linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <1487261386-2641-5-git-send-email-peter.huewe@infineon.com>
Date:   Thu, 16 Feb 2017 16:09:46 +0000
From:   Peter Huewe <peter.huewe@...ineon.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        <tpmdd-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <peterhuewe@....de>,
        Christophe Ricard <christophe-h.ricard@...com>,
        "Peter Huewe" <peter.huewe@...ineon.com>, <stable@...r.kernel.org>,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer

Testing the implementation with a Raspberry Pi 2 showed that under some
circumstances its SPI master erroneously releases the CS line before the
transfer is complete, i.e. before the end of the last clock. In this case
the TPM ignores the transfer and misses for example the GO command. The
driver is unable to detect this communication problem and will wait for a
command response that is never going to arrive, timing out eventually.

As a workaround, the small delay ensures that the CS line is held long
enough, even with a faulty SPI master. Other SPI masters are not affected,
except for a negligible performance penalty.

Cc: <stable@...r.kernel.org>
Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
Signed-off-by: Peter Huewe <peter.huewe@...ineon.com>
---
 drivers/char/tpm/tpm_tis_spi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index b50c5b072df3..685c51bf5d7e 100644
--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -110,6 +110,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,

 		spi_xfer.cs_change = 0;
 		spi_xfer.len = transfer_len;
+		spi_xfer.delay_usecs = 5;

 		if (direction) {
 			spi_xfer.tx_buf = NULL;
-- 
2.7.4