• Hao Wu's avatar
    tpm: fix Atmel TPM crash caused by too frequent queries · 79ca6f74
    Hao Wu authored
    The Atmel TPM 1.2 chips crash with error
    `tpm_try_transmit: send(): error -62` since kernel 4.14.
    It is observed from the kernel log after running `tpm_sealdata -z`.
    The error thrown from the command is as follows
    ```
    $ tpm_sealdata -z
    Tspi_Key_LoadKey failed: 0x00001087 - layer=tddl,
    code=0087 (135), I/O error
    ```
    
    The issue was reproduced with the following Atmel TPM chip:
    ```
    $ tpm_version
    T0  TPM 1.2 Version Info:
      Chip Version:        1.2.66.1
      Spec Level:          2
      Errata Revision:     3
      TPM Vendor ID:       ATML
      TPM Version:         01010000
      Manufacturer Info:   41544d4c
    ```
    
    The root cause of the issue is due to the TPM calls to msleep()
    were replaced with usleep_range() [1], which reduces
    the actual timeout. Via experiments, it is observed that
    the original msleep(5) actually sleeps for 15ms.
    Because of a known timeout issue in Atmel TPM 1.2 chip,
    the shorter timeout than 15ms can cause the error described above.
    
    A few further changes in kernel 4.16 [2] and 4.18 [3, 4] further
    reduced the timeout to less than 1ms. With experiments,
    the problematic timeout in the latest kernel is the one
    for `wait_for_tpm_stat`.
    
    To fix it, the patch reverts the timeout of `wait_for_tpm_stat`
    to 15ms for all Atmel TPM 1.2 chips, but leave it untouched
    for Ateml TPM 2.0 chip, and chips from other vendors.
    As explained above, the chosen 15ms timeout is
    the actual timeout before this issue introduced,
    thus the old value is used here.
    Particularly, TPM_ATML_TIMEOUT_WAIT_STAT_MIN is set to 14700us,
    TPM_ATML_TIMEOUT_WAIT_STAT_MIN is set to 15000us according to
    the existing TPM_TIMEOUT_RANGE_US (300us).
    The fixed has been tested in the system with the affected Atmel chip
    with no issues observed after boot up.
    
    References:
    [1] 9f3fc7bc tpm: replace msleep() with usleep_range() in TPM
    1.2/2.0 generic drivers
    [2] cf151a9a tpm: reduce tpm polling delay in tpm_tis_core
    [3] 59f5a6b0 tpm: reduce poll sleep time in tpm_transmit()
    [4] 424eaf91 tpm: reduce polling time to usecs for even finer
    granularity
    
    Fixes: 9f3fc7bc ("tpm: replace msleep() with usleep_range() in TPM 1.2/2.0 generic drivers")
    Link: https://patchwork.kernel.org/project/linux-integrity/patch/20200926223150.109645-1-hao.wu@rubrik.com/Signed-off-by: default avatarHao Wu <hao.wu@rubrik.com>
    Reviewed-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
    Signed-off-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
    79ca6f74
tpm_tis_core.h 4.83 KB