[TF-M] Re: minor bug in an521 protections

Hi Bohdan,

Thanks for spotting this. I went through all the SAU configurations for Arm platforms and did find some missing "-1". Basically they are all veneer regions. Other regions such as NS_DATA_START, DEV_APIS_TEST_NVMEM_REGION_START, they are already defined with "-1". Ideally we should keep consistencies for the region settings regarding where the "-1" should be done. Let's fixhttps://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/18547 the bug first.

Best Regards, Kevin

From: Bohdan.Hunko@infineon.com Bohdan.Hunko@infineon.com Sent: Friday, December 23, 2022 18:34 To: Kevin Peng Kevin.Peng@arm.com; Ken Liu Ken.Liu@arm.com; tf-m@lists.trustedfirmware.org Cc: nd nd@arm.com Subject: RE: minor bug in an521 protections

Hi all,

If -1 in NS_PARTITION_START is intentional why then there is no -1 in same array for some other entries like NS_DATA_START, DEV_APIS_TEST_NVMEM_REGION_START.

-1 should either is always be needed or always not needed.

From Kevin Peng`s explanation looks like it is always needed, so there still is a bug in cases where -1 is not subtracted. If so I think the simpliest solution would be to do -1 when we actually assign to RLAR register and keep array entries without -1.

Regards, Bohdan Hunko

Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com

From: Kevin Peng via TF-M <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Sent: 23 December 2022 05:04 To: Ken Liu <Ken.Liu@arm.commailto:Ken.Liu@arm.com>; tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: [TF-M] Re: minor bug in an521 protections

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Hi Bohdan,

I believe the "-1" is intentional because the SAU does a round-up on limit address.

From the Armv8m spec: [cid:image001.png@01D91AC3.99842720]

In your example, 0x1000_0000 + 0x1000 - 1 = 0x10000FFF The LADDR limit address written to SAU_REGIONn.LADDR will be bits 31:5 of 0x1000_0FE0 (only bits 31:5 stand for the address) (Base address would be 0x1000_0000.) Then the above match would be Address >= 0x1000_0000 && Address <= 0x1000_0FFF (Bit 31:5 of 0x1000_0FE0:'11111') Which matches the expectation.

If you didn't do a "-1", then the match would be: Bit 31:5 of 0x1000_1000 written to LADDR bits of SAU_REGIONn.LADDR. Address >= 0x1000_0000 && Address <= 0x1000_101F (Bit 31:5 of 0x1000_1000:'11111') Which would include 32 bytes more than expectation.

Best Regards, Kevin

From: Ken Liu via TF-M <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Sent: Friday, December 23, 2022 10:04 To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: [TF-M] Re: minor bug in an521 protections

Hi Bohdan,

Thanks for reporting this, will go through all SAU related settings.

/Ken

From: Bohdan.Hunko--- via TF-M <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Sent: Friday, December 23, 2022 4:59 AM To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Subject: [TF-M] minor bug in an521 protections

Hi,

I have been working on TZ stuff recently and found small problem in an521 platform protections. The problem is in SAU config. sau_cfg in platform/ext/target/arm/mps2/an521/target_cfg.c has entry for NSPE code: { ((uint32_t)NS_PARTITION_START), ((uint32_t)NS_PARTITION_START + NS_PARTITION_SIZE - 1), false, }, Where both NS_PARTITION_START and NS_PARTITION_SIZE are 32 bytes aligned, which means that when 1 is subtracted lower 5 bits are getting set to 1, for example: 0x1000_0000 + 0x1000 - 1 = 0x10000FFF Then in sau_and_idau_cfg() function lower 5 bits are cleared by the mask: sau_cfg[i].RLAR & SAU_RLAR_LADDR_Msk

This means that in reality highest 32 bytes of NSPE are protected as Secure in SAU.

Same problem is present for SECONDARY_PARTITION_SIZE SAU entry.

This is not huge problem, but still worth fixing.

I believe other arm and TZ platforms may also have this bug, but I haven't checked in details.

Regards, Bohdan Hunko

Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com