Re: [PATCH] mmc: rpmb: do not force a retune before RPMB switch

Jorge Ramirez-Ortiz, Foundries
2024-01-02T22:02:03Z

On 02/01/24 21:01:52, Adrian Hunter wrote:
> On 2/01/24 12:41, Jorge Ramirez-Ortiz, Foundries wrote:
> > On 11/12/23 09:00:06, Jorge Ramirez-Ortiz, Foundries wrote:
> >> On 06/12/23 11:00:47, Jorge Ramirez-Ortiz, Foundries wrote:
> >>> On 06/12/23 07:02:43, Avri Altman wrote:
> >>>>>
> >>>>> On 4/12/23 17:01, Jorge Ramirez-Ortiz wrote:
> >>>>>> Requesting a retune before switching to the RPMB partition has been
> >>>>>> observed to cause CRC errors on the RPMB reads (-EILSEQ).
> >>>>>
> >>>>> There are still 2 concerns:
> >>>>> 1) We don't really know the root cause. Have you determined if here are
> >>>>> CRC errors in the main partition also?
> >>>
> >>> right, and I don't disagree with that.
> >>>
> >>> As a test I created a 4GB file from /dev/random which I then copied
> >>> several times (dd if= ....)
> >>>
> >>> root@uz3cg-dwg-sec:/sys/kernel/debug/mmc0# cat err_stats
> >>> # Command Timeout Occurred: 0
> >>> # Command CRC Errors Occurred: 0
> >>> # Data Timeout Occurred: 0
> >>> # Data CRC Errors Occurred: 0
> >>> # Auto-Cmd Error Occurred: 0
> >>> # ADMA Error Occurred: 0
> >>> # Tuning Error Occurred: 0
> >>> # CMDQ RED Errors: 0
> >>> # CMDQ GCE Errors: 0
> >>> # CMDQ ICCE Errors: 0
> >>> # Request Timedout: 0
> >>> # CMDQ Request Timedout: 0
> >>> # ICE Config Errors: 0
> >>> # Controller Timedout errors: 0
> >>> # Unexpected IRQ errors: 0
> >>>
> >>> However as soon as I access RPMB and fails (it takes just a few tries) I see:
> >>>
> >>> I/TC: RPMB: Using generated key
> >>> [ 86.902118] sdhci-arasan ff160000.mmc: __mmc_blk_ioctl_cmd: data error -84
> >>> E/TC:? 0
> >>> E/TC:? 0 TA panicked with code 0xffff0000
> >>> E/LD: Status of TA 22250a54-0bf1-48fe-8002-7b20f1c9c9b1
> >>> E/LD: arch: aarch64
> >>> E/LD: region 0: va 0xc0004000 pa 0x7e200000 size 0x002000 flags rw-s (ldelf)
> >>> E/LD: region 1: va 0xc0006000 pa 0x7e202000 size 0x008000 flags r-xs (ldelf)
> >>> E/LD: region 2: va 0xc000e000 pa 0x7e20a000 size 0x001000 flags rw-s (ldelf)
> >>> E/LD: region 3: va 0xc000f000 pa 0x7e20b000 size 0x004000 flags rw-s (ldelf)
> >>> E/LD: region 4: va 0xc0013000 pa 0x7e20f000 size 0x001000 flags r--s
> >>> E/LD: region 5: va 0xc0014000 pa 0x7e22c000 size 0x005000 flags rw-s (stack)
> >>> E/LD: region 6: va 0xc0019000 pa 0x818ea9ba8 size 0x002000 flags rw-- (param)
> >>> E/LD: region 7: va 0xc001b000 pa 0x818e97ba8 size 0x001000 flags rw-- (param)
> >>> E/LD: region 8: va 0xc004f000 pa 0x00001000 size 0x014000 flags r-xs [0]
> >>> E/LD: region 9: va 0xc0063000 pa 0x00015000 size 0x008000 flags rw-s [0]
> >>> E/LD: [0] 22250a54-0bf1-48fe-8002-7b20f1c9c9b1 @ 0xc004f000
> >>> E/LD: Call stack:
> >>> E/LD: 0xc0051a14
> >>> E/LD: 0xc004f31c
> >>> E/LD: 0xc0052d40
> >>> E/LD: 0xc004f624
> >>>
> >>> root@uz3cg-dwg-sec:/var/rootdirs/home/fio# cat /sys/kernel/debug/mmc0/err_stats
> >>> # Command Timeout Occurred: 0
> >>> # Command CRC Errors Occurred: 0
> >>> # Data Timeout Occurred: 0
> >>> # Data CRC Errors Occurred: 1
> >>> # Auto-Cmd Error Occurred: 0
> >>> # ADMA Error Occurred: 0
> >>> # Tuning Error Occurred: 0
> >>> # CMDQ RED Errors: 0
> >>> # CMDQ GCE Errors: 0
> >>> # CMDQ ICCE Errors: 0
> >>> # Request Timedout: 0
> >>> # CMDQ Request Timedout: 0
> >>> # ICE Config Errors: 0
> >>> # Controller Timedout errors: 0
> >>> # Unexpected IRQ errors: 0
> >>>
> >>>>> 2) Forcing this on everyone
> >>>>>
> >>>>> The original idea was that because re-tuning cannot be done in RPMB, the
> >>>>> need to re-rune in RPMB could be avoided by always re-tuning before
> >>>>> switching to RPMB and then switching straight back. IIRC re-tuning should
> >>>>> guarantee at least 4MB more I/O without issue.
> >>>> Performance is hardly an issue in the context of RPMB access -
> >>>> For most cases it’s a single frame.
> >>>
> >>> Yes, the security use case typically stores hashes, variables
> >>> (bootcount, upgrade_available, versions, that sort of thing) and
> >>> certificates in RPMB.
> >>>
> >>> Since you mentioned, I am seeing that tuning before switching to RPMB
> >>> has an impact on performance. As a practical test, just reading a 6 byte
> >>> variable incurs in 50ms penalty in kernel space due to the need to
> >>> retune 5 times. Not great since the request is coming from a Trusted
> >>> Application via OP-TEE through the supplicant meaning this TEE thread
> >>> (they are statically allocated CFG_NUM_THREADS) will be reserved for
> >>> quite a bit of time.
> >>>
> >>> Roughly:
> >>> TA --> OP-TEE (core) --> TEE-supplicant --> Kernel (>50ms) --> OP-TEE --> TA
> >>
> >> To add more detail to the timing above, when using RPMB, OP-TEE stores
> >> the secure filesystem on RPMB as well, so accessing one of the variables
> >> stored in the filesystem consists on a number (~5) of individual RPMB
> >> requests (each one forcing a retune, each retune taking around 10ms).
> >
> > Adrian, please could you comment on the above.
> >
> > The current code is a performance drag for systems that implement their
> > secure filesystems on RPMB (i.e: OP-TEE) causing each read operation (of
> > variables consisting of a few bytes stored in such a filesystem) to
> > perform 5 consecutive retune requests.
> >
> > I am just thinking whether the original use case that forces a call to
> > retune prior to processing the RPMB request remains valid.
>
> I am not sure what you are asking.
>
> For some transfer modes, re-tuning is expected to deal with sampling
> point drift over time, mainly due to temperature changes. It is done
> either periodically (tuning timer) or after a CRC error.
>
> There is no reason to assume RPMB is immune from that.
>
> Certainly re-tuning before switching to RPMB is not optimal for
> performance, and we can leave that out, but a CRC error before
> or during RPMB operations will *still* result in re-tuning
> after switching back from RPMB.
>
> In your case, re-tuning makes things worse, which is a bit of a
> mystery. Running the new re-tuning test would tell us whether
> it makes things worse in general, or only for RPMB.
>
> >
> > Independently of the fact that not doing so fixes the problem I was
> > working on - and with the information I have - I dont think RPMB is
> > generally used to store larger files (maybe you have more information
> > about the average use case? are you aware of systems using RPMB to store
> > binaries or images?)
> >
> > I still I have to execute the test you shared some weeks ago. Bit of a
> > pain to NFS boot this system...will try to do it this week.
>
> Other options are to boot with an initrd only, or after boot switch
> to a RAM-based file system.
>
> I was waiting for this, since it is good to try to get closer to a
> root cause, but as you point out, the change is good for performance
> also, so I will Ack it.

great, thanks!
I was finally able to nfs mount this project (was a bit of a pain since
the board is using ostree).

The test failed. See below

root@uz3cg-dwg-sec:/# uname -a
Linux uz3cg-dwg-sec 5.15.64-lmp-standard #1 SMP Thu Sep 1 02:40:19 UTC 2022 aarch64 GNU/Linux

root@uz3cg-dwg-sec:/# cat /proc/cmdline
earlycon console=ttyPS0,115200 clk_ignore_unused root=/dev/nfs nfsroot=192.168.1.9:/srv/nfs/rootfs rootwait rw nfsrootdebug ip=dhcp rootfstype=ext4 ostree=ostree/boot.1.1/lmp/5c73dc21eb70c12363747b90c04302115715fa46063a9099841cf23cc70c09a6/0

root@uz3cg-dwg-sec:/sys/bus/mmc/drivers# cd mmcblk/

root@uz3cg-dwg-sec:/sys/bus/mmc/drivers/mmcblk# ls
bind mmc0:0001 uevent unbind

root@uz3cg-dwg-sec:/sys/bus/mmc/drivers/mmcblk# echo 'mmc0:0001' > unbind

root@uz3cg-dwg-sec:/sys/bus/mmc/drivers# echo 'mmc0:0001' > mmc_test/bind
[ 284.253261] mmc_test mmc0:0001: Card claimed for testing.

root@uz3cg-dwg-sec:/sys/bus/mmc/drivers# cd ..
root@uz3cg-dwg-sec:/sys/bus/mmc# ls
devices drivers drivers_autoprobe drivers_probe uevent

root@uz3cg-dwg-sec:/sys/bus/mmc# cd /

root@uz3cg-dwg-sec:/# cat /sys/kernel/debug/mmc0/mmc0\:0001/test
test testlist

root@uz3cg-dwg-sec:/# cat /sys/kernel/debug/mmc0/mmc0\:0001/testlist | grep tuning
52: Re-tuning reliability

root@uz3cg-dwg-sec:/# echo 52 > /sys/kernel/debug/mmc0/mmc0\:0001/test
[ 352.283447] mmc0: Starting tests of card mmc0:0001...
[ 352.288597] mmc0: Test case 52. Re-tuning reliability...
[ 354.265441] mmc0: Result: ERROR (-84)
[ 354.269142] mmc0: Tests completed.

root@uz3cg-dwg-sec:/#

>
>
> >
> > TIA
> >
> >>
> >> BTW, I also tried delaying the timing between those consecutive retunes
> >> (up to 1 second), but the issue still persisted.
> >>
> >>>
> >>> Adrian, I couldn't find the original performance justification for
> >>> enabling this feature globally. At which point do you think it becomes
> >>> beneficial to retune before accessing RPMB?
> >>
> >> How should we proceed with this patch then? can it be merged as I
> >> proposed? should I rewrite it differently? not sure what is next
> >>
> >> TIA
> >> Jorge
>