Re: [PATCH v2 3/4] cmd: optee_rpmb: allocate large enough buffer when reading persistent value

[Mattijs Korpershoek <mkorpershoek@kernel.org>]

Hi Rasmus,

Thank you for the patch.

On Thu, Sep 03, 2026 at 23:22, Rasmus Villemoes <ravi@prevas.dk> wrote:

> It is implied by the comments in avb_ops.h and the translation of
> TEE_ERROR_STORAGE_NO_SPACE to AVB_IO_RESULT_ERROR_INSUFFICIENT_SPACE
> done in common/avb_verify.c:invoke_func() that the
> TA_AVB_CMD_READ_PERSIST_VALUE could return TEE_ERROR_STORAGE_NO_SPACE
> when the value is longer than the passed buffer size, and that
> param[1].u.memref.size would be set to the actual size, so that one
> can allocate an appropriate buffer and re-read.
>
> However, that has AFAICT never been the case; there is no mention of
> TEE_ERROR_STORAGE_NO_SPACE in the history of ta/avb/ in
> https://github.com/OP-TEE/optee_os.git, and what the code does instead
> is to return a value truncated to the given buffer size. In other
> words, not only can one not determine the correct buffer size to
> allocate, one is not even told that truncation happened.
>
> Changing the ABI of the existing TA_AVB_CMD_READ_PERSIST_VALUE method
> to return an error in the case of a too small buffer was
> rejected. Instead, a new TA_AVB_CMD_READ_PERSIST_VALUE2 method is
> implemented which does return an error in case of a too small buffer
> <https://github.com/OP-TEE/optee_os/pull/7959>.
>
> Make use of that method, thus making the <bytes> argument to
> read_pvalue redundant - continue to accept it, but only use it as a
> hint for the initial size, defaulting to 64.
>
> This obviously requires running against an updated op-tee, but as the
> optee_rpmb command so far has not been usable programmatically (the
> values read are only printed to the console), no existing boot logic
> can have been relying on this command.
>
> Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>