Re: [PATCH v4 7/8] tpm_ftpm_tee: Free and unregister TEE shared memory during kexec

[Jarkko Sakkinen]

On Thu, Jun 10, 2021 at 04:09:12PM -0500, Tyler Hicks wrote:
> dma-buf backed shared memory cannot be reliably freed and unregistered
> during a kexec operation even when tee_shm_free() is called on the shm
> from a .shutdown hook. The problem occurs because dma_buf_put() calls
> fput() which then uses task_work_add(), with the TWA_RESUME parameter,
> to queue tee_shm_release() to be called before the current task returns
> to user mode. However, the current task never returns to user mode
> before the kexec completes so the memory is never freed nor
> unregistered.
> 
> Use tee_shm_alloc_kernel_buf() to avoid dma-buf backed shared memory
> allocation so that tee_shm_free() can directly call tee_shm_release().
> This will ensure that the shm can be freed and unregistered during a
> kexec operation.
> 
> Fixes: 09e574831b27 ("tpm/tpm_ftpm_tee: A driver for firmware TPM running inside TEE")
> Fixes: 1760eb689ed6 ("tpm/tpm_ftpm_tee: add shutdown call back")
> Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>


Acked-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

> ---
>  drivers/char/tpm/tpm_ftpm_tee.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_tee.c
> index 2ccdf8ac6994..6e3235565a4d 100644
> --- a/drivers/char/tpm/tpm_ftpm_tee.c
> +++ b/drivers/char/tpm/tpm_ftpm_tee.c
> @@ -254,11 +254,11 @@ static int ftpm_tee_probe(struct device *dev)
>  	pvt_data->session = sess_arg.session;
>  
>  	/* Allocate dynamic shared memory with fTPM TA */
> -	pvt_data->shm = tee_shm_alloc(pvt_data->ctx,
> -				      MAX_COMMAND_SIZE + MAX_RESPONSE_SIZE,
> -				      TEE_SHM_MAPPED | TEE_SHM_DMA_BUF);
> +	pvt_data->shm = tee_shm_alloc_kernel_buf(pvt_data->ctx,
> +						 MAX_COMMAND_SIZE +
> +						 MAX_RESPONSE_SIZE);
>  	if (IS_ERR(pvt_data->shm)) {
> -		dev_err(dev, "%s: tee_shm_alloc failed\n", __func__);
> +		dev_err(dev, "%s: tee_shm_alloc_kernel_buf failed\n", __func__);
>  		rc = -ENOMEM;
>  		goto out_shm_alloc;
>  	}
> -- 
> 2.25.1
> 
> 

/Jarkko