linux-kernel - Re: [PATCH v3 3/4] tpm_tis: Disable interrupts if interrupt storm detected

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Date:   Mon, 07 Dec 2020 11:58:44 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Jerry Snitselaar <jsnitsel@...hat.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Peter Huewe <peterhuewe@....de>,
        Matthew Garrett <mjg59@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH v3 3/4] tpm_tis: Disable interrupts if interrupt storm
 detected

On Mon, 2020-12-07 at 15:28 -0400, Jason Gunthorpe wrote:
> On Sun, Dec 06, 2020 at 08:26:16PM +0100, Thomas Gleixner wrote:
> > Just as a side note. I was looking at tpm_tis_probe_irq_single()
> > and that function is leaking the interrupt request if any of the
> > checks afterwards fails, except for the final interrupt probe check
> > which does a cleanup. That means on fail before that the interrupt
> > handler stays requested up to the point where the module is
> > removed. If that's a shared interrupt and some other device is
> > active on the same line, then each interrupt from that device will
> > call into the TPM code. Something like the below is needed.
> > 
> > Also the X86 autoprobe mechanism is interesting:
> > 
> > 	if (IS_ENABLED(CONFIG_X86))
> > 		for (i = 3; i <= 15; i++)
> > 			if (!tpm_tis_probe_irq_single(chip, intmask, 0,
> > i))
> > 				return;
> > 
> > The third argument is 'flags' which is handed to request_irq(). So
> > that won't ever be able to probe a shared interrupt. But if an
> > interrupt number > 0 is handed to tpm_tis_core_init() the interrupt
> > is requested with IRQF_SHARED. Same issue when the chip has an
> > interrupt number in the register. It's also requested exclusive
> > which is pretty likely to fail on ancient x86 machines.
> 
> It is very likely none of this works any more, it has been repeatedly
> reworked over the years and just left behind out of fear someone
> needs it. I've thought it should be deleted for a while now.
> 
> I suppose the original logic was to try and probe without SHARED
> because a probe would need exclusive access to the interrupt to tell
> if the TPM was actually the source, not some other device.
> 
> It is all very old and very out of step with current thinking, IMHO.
> I skeptical that TPM interrupts were ever valuable enough to deserve
> this in the first place.

For what it's worth, I agree.  Trying to probe all 15 ISA interrupts is
last millennium thinking we should completely avoid.  If it's not
described in ACPI then you don't get an interrupt full stop.

James