Re: [PATCH v2] tpm: Allow system suspend to continue when TPM suspend fails

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Jan 06, 2023 at 04:01:56AM +0100, Jason A. Donenfeld wrote:
> TPM 1 is sometimes broken across system suspends, due to races or
> locking issues or something else that haven't been diagnosed or fixed
> yet, most likely having to do with concurrent reads from the TPM's
> hardware random number generator driver. These issues prevent the system
> from actually suspending, with errors like:
> 
>   tpm tpm0: A TPM error (28) occurred continue selftest
>   ...

<REMOVE>

>   tpm tpm0: A TPM error (28) occurred attempting get random
>   ...
>   tpm tpm0: Error (28) sending savestate before suspend
>   tpm_tis 00:08: PM: __pnp_bus_suspend(): tpm_pm_suspend+0x0/0x80 returns 28
>   tpm_tis 00:08: PM: dpm_run_callback(): pnp_bus_suspend+0x0/0x10 returns 28
>   tpm_tis 00:08: PM: failed to suspend: error 28
>   PM: Some devices failed to suspend, or early wake event detected

</REMOVE>

Unrelated to thix particular fix.

> This issue was partially fixed by 23393c646142 ("char: tpm: Protect
> tpm_pm_suspend with locks"), in a last minute 6.1 commit that Linus took
> directly because the TPM maintainers weren't available. However, it
> seems like this just addresses the most common cases of the bug, rather
> than addressing it entirely. So there are more things to fix still,
> apparently.
> 
> In lieu of actually fixing the underlying bug, just allow system suspend
> to continue, so that laptops still go to sleep fine. Later, this can be
> reverted when the real bug is fixed.
> 
> Link: https://lore.kernel.org/lkml/7cbe96cf-e0b5-ba63-d1b4-f63d2e826efa@suse.cz/
> Cc: stable@vger.kernel.org # 6.1+
> Reported-by: Vlastimil Babka <vbabka@suse.cz>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> This is basically untested and I haven't worked out if there are any
> awful implications of letting the system sleep when TPM suspend fails.
> Maybe some PCRs get cleared and that will make everything explode on
> resume? Maybe it doesn't matter? Somebody well versed in TPMology should
> probably [n]ack this approach.
> 
>  drivers/char/tpm/tpm-interface.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index d69905233aff..6df9067ef7f9 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -412,7 +412,10 @@ int tpm_pm_suspend(struct device *dev)
>  	}
>  
>  suspended:
> -	return rc;
> +	if (rc)
> +		pr_err("Unable to suspend tpm-%d (error %d), but continuing system suspend\n",
> +		       chip->dev_num, rc);
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(tpm_pm_suspend);
>  
> -- 
> 2.39.0
> 

This tpm_tis local issue, nothing to do with tpm_pm_suspend(). Executing
the selftest as part of wake up, is TPM 1.2 dTPM specific requirement, and
the call is located in tpm_tis_resume() [*].

[*] https://lore.kernel.org/lkml/Y8U1QxA4GYvPWDky@kernel.org/

BR, Jarkko