Re: [PATCH v2 0/4] rpmb subsystem, uapi and virtio-rpmb driver

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On 4/6/22 10:19, Bean Huo wrote:
On Wed, 2022-04-06 at 12:22 +0100, Alex Bennée wrote:

Bean Huo <huobean@xxxxxxxxx> writes:

On Tue, 2022-04-05 at 16:43 +0100, Alex Bennée wrote:

Bean Huo <huobean@xxxxxxxxx> writes:

Hi Alex,

Thanks for this unified RPMB interface, I wanted to verify this
on
our
UFS, it seems you didn't add the UFS access interface in this
version
from your userspace tools, right?

No I didn't but it should be easy enough to add some function
pointer
redirection everywhere one of the op_* functions calls a vrpmb_*
function. Do you already have a UFS RPMB device driver?


Hi Alex,
Thanks for your feedback.

We now access UFS RPMB through the RPMB LUN BSG device, RPMB is a
well-
known LU and we have a userspace tool to access it.

I see that if we're going to use your interface, "static struct
rpmb_ops" should be registered from a lower-level driver, for
example
in a UFS driver, yes there should be no problem with this
registration,
but I don't know with the current way Compared, what are the
advantages
to add a driver. maybe the main advantage is that we will have an
unified user space tool for RPMB. right?

Pretty much. The main issue for virtio-rpmb is it doesn't really fit
neatly into the block stack because all it does is the RPMB part so a
non-block orientate API makes sense.

Can you point be to where the UFS driver does it's current RPMB
stuff?


It's the SCSI BSG driver, in fact, we don't have a dedicated UFS RPMB
driver in the kernel. RPMB is a well known LU, we are using userspace
tools to issue SCSI commands directly to the UFS RPMB LU via ioctl()
from the BSG device node in the /dev/sg/ folder.

Here is the BSG part of the code in the userspace tools:

         io_hdr_v4.guard = 'Q';
         io_hdr_v4.protocol = BSG_PROTOCOL_SCSI;
         io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_CMD;
         io_hdr_v4.response = (__u64)sense_buffer;
         io_hdr_v4.max_response_len = SENSE_BUFF_LEN;
         io_hdr_v4.request_len = cmd_len;
         io_hdr_v4.request = (__u64)cdb;
ioctl(fd, SG_IO, &io_hdr_v4))

Hi Bean,

I'm not sure where the above comes from? The Android RPMB client uses slightly different code. Additionally, the retry loop around the submission of SG/IO commands is very important. See also the check_sg_io_hdr() call in send_ufs_rpmb_req(). See also https://cs.android.com/android/platform/superproject/+/master:system/core/trusty/storage/proxy/rpmb.c

Thanks,

Bart.



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