Re: [6.4-rc6] Crash during a kexec operation (tpm_amd_is_rng_defective)

[Jerry Snitselaar]

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@xxxxxxxxxxxxx> 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