(+Paul)
Hi,
On 18/05/2020 02:53, Volodymyr Babchuk wrote:
Trusted Applications use popular approach to determine required size
of buffer: client provides a memory reference with the NULL pointer to
a buffer. This is so called "Null memory reference". TA updates the
NIT: You use double space after '.' here but all the others use a single
space.
reference with the required size and returns it back to client. Then
client allocates buffer of needed size and repeats the operation.
This behavior is described in TEE Client API Specification, paragraph
3.2.5. Memory References.
From the spec, it is not a clear cut that NULL will always used as
fetching the required size of an output buffer. In particular, they
suggest to refer to the protocol.
In your commit message you indirectly point to an example where 0/NULL
would have a different meaning depending on the flags. This is not
explained in the TEE Client API Specification. Do you have some pointer
I could use to check the behavior?
OP-TEE represents this null memory reference as a TMEM parameter with
buf_ptr == NULL. This is the only case when we should allow TMEM
buffer without the OPTEE_MSG_ATTR_NONCONTIG flag.
IIUC, 0 with OPTEE_MSG_ATTR_NONCONTIG set would mean "use the buffer at
address 0" but with the flag cleared, it would mean "return the size".
Am I correct?
Signed-off-by: Volodymyr Babchuk <volodymyr_babc...@epam.com>
The code looks to match your commit message, but I wasn't able to match
it with the spec. Do you have other pointer I could use to check the
behavior?
I assume this wants to be part of Xen 4.14. The change is only for
OP-TEE which is a tech preview feature. So the risk is very limited.
Cheers,
--
Julien Grall
