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Subject: Re: [virtio-comment] Comments on RPMB config space chapter 5.2.14
Harald Mommer <hmo@opensynergy.com> writes: > On 11.03.22 17:02, Huang, Yang wrote: >> >>> 1.) We have an underlying physical RPMB device we would like to forward to >>> a virtual machine via virtio RPMB. Looks like the physical device has a >>> capacity of 256. 256 > 0x80. And 256 also does not fit in the u8 capacity of the >> 256*128KB = 32MB RPMB. What's your flash, eMMC, UFS or NVMe? > > UFS. I should still try to find out what exact chip is used on the > board and try to confirm with the data sheet (if available) that the > capacity of 256 we got from ioctl RPMB_IOC_CAP_CMD is indeed the > correct one. Which means 32MB. just to rule out I'm not fooled by some > obscure bug somewhere in the stack. Which stack would this be? If it's one of my test branches I wouldn't rule out a bug in stack, especially when it comes to handling the config space. There hasn't been a upstream release of an RPMB driver for Linux yet. I'm currently in the middle of having another go that attempts to bridge the gap between a straight dumb frame pass-through and a slightly more ergonomic approach that none the less leaves the cryptographic frame creation to user space. > >>> structure. Thinking now of cutting to 0x80 to fulfill the exact wording of the >>> specification. Alternatively we might violate the specification and cut to 255 >>> which is the biggest value still fitting in u8 capacity. But nothing of this is >>> satisfying. >>> >>> 2.) Looking at the specification the maximum RPMB block count is 256. In our > > I'm referring to the virtio specification as it is currently on latest > master in https://github.com/oasis-tcs/virtio-spec.git. > > 2.) is not about the total size of the RPMB device but about the max. > allowed number of blocks to be read or written at a time in one chunk > (config space max_wr_cnt and max_rd_cnt). While in the text 256B is > still a valid value in the config space this value would not fit into > the u8. Not the issue now but remarkable when we are already in clause > 5.12.4. -- Alex BennÃe
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