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

Jorge Ramirez-Ortiz, Foundries
2023-12-11T11:07:00Z

On 11/12/23 12:25:19, Adrian Hunter wrote:
> On 11/12/23 10:00, 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).
> >
> > 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
>
> It would be good to try to determine if the error happens when the
> switch command comes immediately after tuning. For example, add
> a delay after tuning and see if that makes any difference. e.g.
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index c79f73459915..6b168659282a 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2867,8 +2867,10 @@ int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
>
> ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
> if (!(ctrl & SDHCI_CTRL_EXEC_TUNING)) {
> - if (ctrl & SDHCI_CTRL_TUNED_CLK)
> + if (ctrl & SDHCI_CTRL_TUNED_CLK) {
> + msleep(10);
> return 0; /* Success! */
> + }
> break;
> }
>
>

Thanks Adrian.

The issue sill triggers (in this case on the last but one access to
retrieve the 6 byte variable).

--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2781,6 +2781,7 @@ static int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
* Issue opcode repeatedly till Execute Tuning is set to 0 or the number
* of loops reaches tuning loop count.
*/
+ printk(KERN_ERR "tune starts[loop %d]\n", host->tuning_loop_count);
for (i = 0; i < host->tuning_loop_count; i++) {
u16 ctrl;

@@ -2799,8 +2800,11 @@ static int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)

ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
if (!(ctrl & SDHCI_CTRL_EXEC_TUNING)) {
- if (ctrl & SDHCI_CTRL_TUNED_CLK)
- return 0; /* Success! */
+ if (ctrl & SDHCI_CTRL_TUNED_CLK) {
+ printk(KERN_ERR "tune success[%d]\n", i);
+ msleep(10);
+ return 0; /* Success! */
+ }
break;
}

[ 164.919090] tune starts[loop 40]
[ 164.923152] tune success[39]
[ 164.952106] tune starts[loop 40]
[ 164.956611] tune success[39]
[ 165.084402] tune starts[loop 40]
[ 165.089350] tune success[39]
[ 165.116491] tune starts[loop 40]
[ 165.120806] tune success[39]
[ 165.145016] 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 0x818ac38e8 size 0x001000 flags rw-- (param)
E/LD: region 7: va 0xc001a000 pa 0x818ac36e8 size 0x001000 flags rw-- (param)
E/LD: region 8: va 0xc0022000 pa 0x00001000 size 0x014000 flags r-xs [0]
E/LD: region 9: va 0xc0036000 pa 0x00015000 size 0x008000 flags rw-s [0]
E/LD: [0] 22250a54-0bf1-48fe-8002-7b20f1c9c9b1 @ 0xc0022000
E/LD: Call stack:
E/LD: 0xc0024e58
E/LD: 0xc0022388
E/LD: 0xc0025d40
E/LD: 0xc0022624
[ 166.119598] tune starts[loop 40]
[ 166.125700] tune success[39]