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From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Matthew Garrett <mjg59@google.com>
Cc:     linux-integrity <linux-integrity@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        jarkko@kernel.org, Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Hans de Goede <hdegoede@redhat.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
In-reply-to: <CACdnJuuAyBYacCiOOZ8-L-0Xnfa3+pCVY_oejOJ8RPzuG2QgrQ@mail.gmail.com>
Date:   Wed, 18 Nov 2020 23:36:20 -0700
Message-ID: <87d009c0pn.fsf@redhat.com>
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Matthew Garrett @ 2020-10-15 15:39 MST:

> On Thu, Oct 15, 2020 at 2:44 PM Jerry Snitselaar <jsnitsel@redhat.com> wrote:
>>
>> There is a misconfiguration in the bios of the gpio pin used for the
>> interrupt in the T490s. When interrupts are enabled in the tpm_tis
>> driver code this results in an interrupt storm. This was initially
>> reported when we attempted to enable the interrupt code in the tpm_tis
>> driver, which previously wasn't setting a flag to enable it. Due to
>> the reports of the interrupt storm that code was reverted and we went back
>> to polling instead of using interrupts. Now that we know the T490s problem
>> is a firmware issue, add code to check if the system is a T490s and
>> disable interrupts if that is the case. This will allow us to enable
>> interrupts for everyone else. If the user has a fixed bios they can
>> force the enabling of interrupts with tpm_tis.interrupts=1 on the
>> kernel command line.
>
> I think an implication of this is that systems haven't been
> well-tested with interrupts enabled. In general when we've found a
> firmware issue in one place it ends up happening elsewhere as well, so
> it wouldn't surprise me if there are other machines that will also be
> unhappy with interrupts enabled. Would it be possible to automatically
> detect this case (eg, if we get more than a certain number of
> interrupts in a certain timeframe immediately after enabling the
> interrupt) and automatically fall back to polling in that case? It
> would also mean that users with fixed firmware wouldn't need to pass a
> parameter.

I believe Matthew is correct here. I found another system today
with completely different vendor for both the system and the tpm chip.
In addition another Lenovo model, the L490, has the issue.

This initial attempt at a solution like Matthew suggested works on
the system I found today, but I imagine it is all sorts of wrong.
In the 2 systems where I've seen it, there are about 100000 interrupts
in around 1.5 seconds, and then the irq code shuts down the interrupt
because they aren't being handled.


diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 49ae09ac604f..478e9d02a3fa 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -27,6 +27,11 @@
 #include "tpm.h"
 #include "tpm_tis_core.h"

+static unsigned int time_start = 0;
+static bool storm_check = true;
+static bool storm_killed = false;
+static u32 irqs_fired = 0;
+
 static void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value);

 static void tpm_tis_enable_interrupt(struct tpm_chip *chip, u8 mask)
@@ -464,25 +469,31 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const u8 *buf, size_t len)
        return rc;
 }

-static void disable_interrupts(struct tpm_chip *chip)
+static void __disable_interrupts(struct tpm_chip *chip)
 {
        struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
        u32 intmask;
        int rc;

-       if (priv->irq == 0)
-               return;
-
        rc = tpm_tis_read32(priv, TPM_INT_ENABLE(priv->locality), &intmask);
        if (rc < 0)
                intmask = 0;

        intmask &= ~TPM_GLOBAL_INT_ENABLE;
        rc = tpm_tis_write32(priv, TPM_INT_ENABLE(priv->locality), intmask);
+       chip->flags &= ~TPM_CHIP_FLAG_IRQ;
+}
+
+static void disable_interrupts(struct tpm_chip *chip)
+{
+       struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);

+       if (priv->irq == 0)
+               return;
+
+       __disable_interrupts(chip);
        devm_free_irq(chip->dev.parent, priv->irq, chip);
        priv->irq = 0;
-       chip->flags &= ~TPM_CHIP_FLAG_IRQ;
 }

 /*
@@ -528,6 +539,12 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
        int rc, irq;
        struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);

+       if (unlikely(storm_killed)) {
+               devm_free_irq(chip->dev.parent, priv->irq, chip);
+               priv->irq = 0;
+               storm_killed = false;
+       }
+
        if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
                return tpm_tis_send_main(chip, buf, len);

@@ -748,6 +765,21 @@ static irqreturn_t tis_int_handler(int dummy, void *dev_id)
        u32 interrupt;
        int i, rc;

+       if (storm_check) {
+               irqs_fired++;
+
+               if (!time_start) {
+                       time_start = jiffies_to_msecs(jiffies);
+               } else if ((irqs_fired > 1000) && (jiffies_to_msecs(jiffies) - jiffies < 500)) {
+                       __disable_interrupts(chip);
+                       storm_check = false;
+                       storm_killed = true;
+                       return IRQ_HANDLED;
+               } else if ((jiffies_to_msecs(jiffies) - time_start > 500) && (irqs_fired < 1000)) {
+                       storm_check = false;
+               }
+       }
+
        rc = tpm_tis_read32(priv, TPM_INT_STATUS(priv->locality), &interrupt);
        if (rc < 0)
                return IRQ_NONE;