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

[Hao Wu <hao.wu@rubrik.com>]

Applied the fix on 5.9-rc4, but it looks like it is not enough to fix the issue. There should be other TPM timing changes since 4.15 (where we have tested and ensure it works). Need to look into it a bit to see what should be the fix in the master branch.

Thanks
Hao

> On Sep 13, 2020, at 11:13 PM, Hao Wu <hao.wu@rubrik.com> 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
>