From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jarkko Sakkinen <jarkko@kernel.org>
To: op-tee@lists.trustedfirmware.org
Subject: Re: [PATCH v4 7/8] tpm_ftpm_tee: Free and unregister TEE shared
 memory during kexec
Date: Tue, 15 Jun 2021 16:04:11 +0300
Message-ID: <20210615130411.hvpnaxnhimjloiz3@kernel.org>
In-Reply-To: <20210610210913.536081-8-tyhicks@linux.microsoft.com>
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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.
>=20
> 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.
>=20
> Fixes: 09e574831b27 ("tpm/tpm_ftpm_tee: A driver for firmware TPM running i=
nside TEE")
> Fixes: 1760eb689ed6 ("tpm/tpm_ftpm_tee: add shutdown call back")
> Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>


Acked-by: Jarkko Sakkinen <jarkko@kernel.org>

> ---
>  drivers/char/tpm/tpm_ftpm_tee.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>=20
> diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_te=
e.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 =3D sess_arg.session;
> =20
>  	/* Allocate dynamic shared memory with fTPM TA */
> -	pvt_data->shm =3D tee_shm_alloc(pvt_data->ctx,
> -				      MAX_COMMAND_SIZE + MAX_RESPONSE_SIZE,
> -				      TEE_SHM_MAPPED | TEE_SHM_DMA_BUF);
> +	pvt_data->shm =3D 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 =3D -ENOMEM;
>  		goto out_shm_alloc;
>  	}
> --=20
> 2.25.1
>=20
>=20

/Jarkko

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