linux-kernel - Re: [6.4-rc6] Crash during a kexec operation (tpm_amd_is_rng

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Date:   Thu, 29 Jun 2023 10:06:47 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     "Limonciello, Mario" <mario.limonciello@....com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Linux regressions mailing list <regressions@...ts.linux.dev>,
        Sachin Sant <sachinp@...ux.ibm.com>,
        open list <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, jarkko@...nel.org,
        linux-integrity@...r.kernel.org
Subject: Re: [6.4-rc6] Crash during a kexec operation
 (tpm_amd_is_rng_defective)

On Thu, Jun 22, 2023 at 09:38:04AM -0500, Limonciello, Mario wrote:
> 
> On 6/22/2023 7:36 AM, Michael Ellerman wrote:
> > "Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info> writes:
> > > Hi, Thorsten here, the Linux kernel's regression tracker. Top-posting
> > > for once, to make this easily accessible to everyone.
> > > 
> > > As Linus will likely release 6.4 on this or the following Sunday a quick
> > > question: is there any hope this regression might be fixed any time
> > > soon?
> > No.
> > 
> > I have added the author of the commit to Cc, maybe they can help?
> > 
> > The immediate question is, is it expected for chip->ops to be NULL in
> > this path? Obviously on actual AMD systems that isn't the case,
> > otherwise the code would crash there. But is the fact that chip->ops is
> > NULL a bug in the ibmvtpm driver, or a possibility that has been
> > overlooked by the checking code.
> > 
> > cheers
> 
> All that code assumes that the TPM is still functional which
> seems not to be the case for your TPM.
> 
> This should fix it:
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 5be91591cb3b..7082b031741e 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -525,6 +525,9 @@ static bool tpm_amd_is_rng_defective(struct tpm_chip
> *chip)
>         u64 version;
>         int ret;
> 
> +       if (!chip->ops)
> +               return false;
> +
>         if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
>                 return false;


Should tpm_amd_is_rng_defective compile to nothing on non-x86 architectures? This code is all about
working around an issue with the AMD fTPM, right?

Regards,
Jerry