Hi Bohdan,

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

From the Armv8m spec:

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.org>
Sent: Friday, December 23, 2022 10:04
To: tf-m@lists.trustedfirmware.org
Cc: nd <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.org>
Sent: Friday, December 23, 2022 4:59 AM
To: 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.com