Re: [PATCH] Fix Atmel TPM crash caused by too frequent queries

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Sep 13, 2020 at 11:13:43PM -0700, Hao Wu wrote:
> Since kernel 4.14, we fixed the TPM sleep logic
> from msleep to usleep_range, so that the TPM
> sleeps exactly with TPM_TIMEOUT (=5ms) afterward.
> Before that fix, msleep(5) actually sleeps for
> around 15ms.
> The fix is https://github.com/torvalds/linux/commit/9f3fc7bcddcb51234e23494531f93ab60475e1c3
> 
> That fix uncovered that the TPM_TIMEOUT was not properly
> set previously. We recently found the TPM driver in kernel 4.14+
> (including 5.9-rc4) crashes Atmel TPM chips with
> too frequent TPM queries.
> 
> The TPM crash signature is
> ```
> $ tpm_sealdata -z
> Tspi_Key_LoadKey failed: 0x00001087 - layer=tddl, code=0087 (135), I/O error
> 
> $ sudo dmesg | grep tpm0
> [59154.665549] tpm tpm0: tpm_try_transmit: send(): error -62
> [59154.809532] tpm tpm0: tpm_try_transmit: send(): error -62
> ```
> 
> >From the error code "-62", it looks similar to another bug
> https://patchwork.kernel.org/patch/10520247/
> where the "TPM_TIMEOUT_USECS_MAX" and "TPM_TIMEOUT_USEC_MIN"
> is too small, which causes TPM get queried too frequently,
> and thus crashes.
> 
> This patch fix the TPM_TIMEOUT to 15ms which was
> the actual timeout TPM chips use before the fix
> from msleep to usleep_range. Thus fixed the crash.
> 
> Test Plan:
> - Run fixed kernel on system with Atmel TPM chips
>   and ensure crash does not happen
> - Run fixed kernel on system with other TPM chips
>   (IFX / WEC / STM) ensure not breakages from tpm-tool
> ---
>  drivers/char/tpm/tpm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 947d1db0a5cc..73259ac0a997 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -37,7 +37,7 @@
>  #define TPM_RETRY		50
>  
>  enum tpm_timeout {
> -	TPM_TIMEOUT = 5,	/* msecs */
> +	TPM_TIMEOUT = 15,	/* msecs */
>  	TPM_TIMEOUT_RETRY = 100, /* msecs */
>  	TPM_TIMEOUT_RANGE_US = 300,	/* usecs */
>  	TPM_TIMEOUT_POLL = 1,	/* msecs */
> -- 
> 2.17.1
> 

Hi,

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