linux-kernel - Re: [PATCH v2] tpm/ppi: remove impossible assertion in tpm_eval

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Date:   Thu, 19 Dec 2019 02:05:34 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Aditya Pakki <pakki001@....edu>
Cc:     kjlu@....edu, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm/ppi: remove impossible assertion in tpm_eval_dsm

On Wed, 2019-12-18 at 09:48 -0600, Aditya Pakki wrote:
> In tpm_eval_dsm, BUG_ON on ppi_handle is used as an assertion.
> However, if ppi_handle is NULL, the kernel crashes. The patch
> removes the unnecessary check.
> 
> Signed-off-by: Aditya Pakki <pakki001@....edu>
> ---
> v1: replaced the recovery code to completely eliminate the check,
> as suggested by Jason Gunthorpe.
> ---
>  drivers/char/tpm/tpm_ppi.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_ppi.c b/drivers/char/tpm/tpm_ppi.c
> index b2dab941cb7f..603f7806f9af 100644
> --- a/drivers/char/tpm/tpm_ppi.c
> +++ b/drivers/char/tpm/tpm_ppi.c
> @@ -42,7 +42,6 @@ static inline union acpi_object *
>  tpm_eval_dsm(acpi_handle ppi_handle, int func, acpi_object_type type,
>  	     union acpi_object *argv4, u64 rev)
>  {
> -	BUG_ON(!ppi_handle);
>  	return acpi_evaluate_dsm_typed(ppi_handle, &tpm_ppi_guid,
>  				       rev, func, argv4, type);
>  }

Hmm.. maybe omitting completely is actually better idea (since
it never should happen anyway).

Lets go with that.

Thanks.

/Jarkko