linux-kernel - [PATCH 2/2] tpm: Prevent hwrng from activating during resume

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Date:   Wed, 26 Apr 2023 20:29:28 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     stable@...r.kernel.org
Subject: [PATCH 2/2] tpm: Prevent hwrng from activating during resume

Set TPM_CHIP_FLAG_SUSPENDED in tpm_pm_suspend() and reset in
tpm_pm_resume(). While the flag is set, tpm_hwrng() gives back zero bytes.
This prevents hwrng from racing during resume.

Cc: stable@...r.kernel.org
Fixes: 6e592a065d51 ("tpm: Move Linux RNG connection to hwrng")
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
 drivers/char/tpm/tpm-chip.c      |  4 ++++
 drivers/char/tpm/tpm-interface.c | 10 ++++++++++
 include/linux/tpm.h              | 13 +++++++------
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 6fdfa65a00c3..6f5ee27aeda1 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -572,6 +572,10 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 {
 	struct tpm_chip *chip = container_of(rng, struct tpm_chip, hwrng);
 
+	/* Give back zero bytes, as TPM chip has not yet fully resumed: */
+	if (chip->flags & TPM_CHIP_FLAG_SUSPENDED)
+		return 0;
+
 	return tpm_get_random(chip, data, max);
 }
 
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 7e513b771832..0f941cb32eb1 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -412,6 +412,8 @@ int tpm_pm_suspend(struct device *dev)
 	}
 
 suspended:
+	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
+
 	if (rc)
 		dev_err(dev, "Ignoring error %d while suspending\n", rc);
 	return 0;
@@ -429,6 +431,14 @@ int tpm_pm_resume(struct device *dev)
 	if (chip == NULL)
 		return -ENODEV;
 
+	chip->flags &= ~TPM_CHIP_FLAG_SUSPENDED;
+
+	/*
+	 * Guarantee that SUSPENDED is written last, so that hwrng does not
+	 * activate before the chip has been fully resumed.
+	 */
+	wmb();
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tpm_pm_resume);
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 4dc97b9f65fb..d7073dc45444 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -274,13 +274,14 @@ enum tpm2_cc_attrs {
 #define TPM_VID_ATML     0x1114
 
 enum tpm_chip_flags {
-	TPM_CHIP_FLAG_TPM2		= BIT(1),
-	TPM_CHIP_FLAG_IRQ		= BIT(2),
-	TPM_CHIP_FLAG_VIRTUAL		= BIT(3),
-	TPM_CHIP_FLAG_HAVE_TIMEOUTS	= BIT(4),
-	TPM_CHIP_FLAG_ALWAYS_POWERED	= BIT(5),
+	TPM_CHIP_FLAG_SUSPENDED			= BIT(0),
+	TPM_CHIP_FLAG_TPM2			= BIT(1),
+	TPM_CHIP_FLAG_IRQ			= BIT(2),
+	TPM_CHIP_FLAG_VIRTUAL			= BIT(3),
+	TPM_CHIP_FLAG_HAVE_TIMEOUTS		= BIT(4),
+	TPM_CHIP_FLAG_ALWAYS_POWERED		= BIT(5),
 	TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED	= BIT(6),
-	TPM_CHIP_FLAG_FIRMWARE_UPGRADE	= BIT(7),
+	TPM_CHIP_FLAG_FIRMWARE_UPGRADE		= BIT(7),
 };
 
 #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
-- 
2.39.2