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SubjectRe: [PATCH 2/3] optee: add FF-A capability OPTEE_FFA_SEC_CAP_ARG_OFFSET
On Wed, 2 Mar 2022 at 01:18, Jens Wiklander <jens.wiklander@linaro.org> wrote:
>
> Adds the secure capability OPTEE_FFA_SEC_CAP_ARG_OFFSET to indicate that
> OP-TEE with FF-A can support an argument struct at a non-zero offset into
> a passed shared memory object.
>

It isn't clear to me why FF-A ABI requires this capability.
shm->offset should be honoured by default, if it isn't then it's a
bug. AFAIK, FF-A is currently still in its early stages so it
shouldn't be that hard to fix bugs in the ABI.

-Sumit

> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
> ---
> drivers/tee/optee/ffa_abi.c | 17 +++++++++++++++--
> drivers/tee/optee/optee_ffa.h | 12 +++++++++++-
> 2 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tee/optee/ffa_abi.c b/drivers/tee/optee/ffa_abi.c
> index 7686f7020616..cc863aaefcd9 100644
> --- a/drivers/tee/optee/ffa_abi.c
> +++ b/drivers/tee/optee/ffa_abi.c
> @@ -615,12 +615,21 @@ static int optee_ffa_do_call_with_arg(struct tee_context *ctx,
> .data0 = OPTEE_FFA_YIELDING_CALL_WITH_ARG,
> .data1 = (u32)shm->sec_world_id,
> .data2 = (u32)(shm->sec_world_id >> 32),
> - .data3 = shm->offset,
> + .data3 = 0,
> };
> struct optee_msg_arg *arg;
> unsigned int rpc_arg_offs;
> struct optee_msg_arg *rpc_arg;
>
> + /*
> + * The shared memory object has to start on a page when passed as
> + * an argument struct. This is also what the shm pool allocator
> + * returns, but check this before calling secure world to catch
> + * eventual errors early in case something changes.
> + */
> + if (shm->offset)
> + return -EINVAL;
> +
> arg = tee_shm_get_va(shm, 0);
> if (IS_ERR(arg))
> return PTR_ERR(arg);
> @@ -678,6 +687,7 @@ static bool optee_ffa_api_is_compatbile(struct ffa_device *ffa_dev,
>
> static bool optee_ffa_exchange_caps(struct ffa_device *ffa_dev,
> const struct ffa_dev_ops *ops,
> + u32 *sec_caps,
> unsigned int *rpc_param_count)
> {
> struct ffa_send_direct_data data = { OPTEE_FFA_EXCHANGE_CAPABILITIES };
> @@ -694,6 +704,7 @@ static bool optee_ffa_exchange_caps(struct ffa_device *ffa_dev,
> }
>
> *rpc_param_count = (u8)data.data1;
> + *sec_caps = data.data2;
>
> return true;
> }
> @@ -777,6 +788,7 @@ static int optee_ffa_probe(struct ffa_device *ffa_dev)
> struct tee_device *teedev;
> struct tee_context *ctx;
> struct optee *optee;
> + u32 sec_caps;
> int rc;
>
> ffa_ops = ffa_dev_ops_get(ffa_dev);
> @@ -788,7 +800,8 @@ static int optee_ffa_probe(struct ffa_device *ffa_dev)
> if (!optee_ffa_api_is_compatbile(ffa_dev, ffa_ops))
> return -EINVAL;
>
> - if (!optee_ffa_exchange_caps(ffa_dev, ffa_ops, &rpc_param_count))
> + if (!optee_ffa_exchange_caps(ffa_dev, ffa_ops, &sec_caps,
> + &rpc_param_count))
> return -EINVAL;
>
> optee = kzalloc(sizeof(*optee), GFP_KERNEL);
> diff --git a/drivers/tee/optee/optee_ffa.h b/drivers/tee/optee/optee_ffa.h
> index ee3a03fc392c..97266243deaa 100644
> --- a/drivers/tee/optee/optee_ffa.h
> +++ b/drivers/tee/optee/optee_ffa.h
> @@ -81,8 +81,16 @@
> * as the second MSG arg struct for
> * OPTEE_FFA_YIELDING_CALL_WITH_ARG.
> * Bit[31:8]: Reserved (MBZ)
> - * w5-w7: Note used (MBZ)
> + * w5: Bitfield of secure world capabilities OPTEE_FFA_SEC_CAP_* below,
> + * unused bits MBZ.
> + * w6-w7: Not used (MBZ)
> + */
> +/*
> + * Secure world supports giving an offset into the argument shared memory
> + * object, see also OPTEE_FFA_YIELDING_CALL_WITH_ARG
> */
> +#define OPTEE_FFA_SEC_CAP_ARG_OFFSET BIT(0)
> +
> #define OPTEE_FFA_EXCHANGE_CAPABILITIES OPTEE_FFA_BLOCKING_CALL(2)
>
> /*
> @@ -112,6 +120,8 @@
> * OPTEE_MSG_GET_ARG_SIZE(num_params) follows a struct optee_msg_arg
> * for RPC, this struct has reserved space for the number of RPC
> * parameters as returned by OPTEE_FFA_EXCHANGE_CAPABILITIES.
> + * MBZ unless the bit OPTEE_FFA_SEC_CAP_ARG_OFFSET is received with
> + * OPTEE_FFA_EXCHANGE_CAPABILITIES.
> * w7: Not used (MBZ)
> * Resume from RPC. Register usage:
> * w3: Service ID, OPTEE_FFA_YIELDING_CALL_RESUME
> --
> 2.31.1
>

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