Why does the firmware memory region have no permissions? | opensbi

(off-list ancestor, not in this archive)

-----Original Message-----
From: Anup Patel [mailto:Anup.Patel at wdc.com]
Sent: Wednesday, June 2, 2021 11:15 PM
To: Chang, Abner (HPS SW/FW Technologist) <redacted>;
Daniel Schaefer [off-list ref]
Cc: opensbi at lists.infradead.org
Subject: RE: Why does the firmware memory region have no permissions?

-----Original Message-----
From: Chang, Abner (HPS SW/FW Technologist) <redacted>
Sent: 02 June 2021 20:19
To: Chang, Abner (HPS SW/FW Technologist) <redacted>;
Anup
Patel [off-list ref]; Daniel Schaefer
[off-list ref]
Cc: opensbi at lists.infradead.org
Subject: RE: Why does the firmware memory region have no permissions?

-----Original Message-----
From: opensbi [mailto:opensbi-bounces at lists.infradead.org] On Behalf
Of Chang, Abner (HPS SW/FW Technologist)
Sent: Saturday, May 15, 2021 11:30 PM
To: Anup Patel <redacted>; Daniel Schaefer
[off-list ref]
Cc: opensbi at lists.infradead.org
Subject: RE: Why does the firmware memory region have no permissions?

-----Original Message-----
From: Anup Patel [mailto:Anup.Patel at wdc.com]
Sent: Saturday, May 15, 2021 4:09 PM
To: Chang, Abner (HPS SW/FW Technologist) <redacted>;
Daniel
Schaefer [off-list ref]
Cc: opensbi at lists.infradead.org
Subject: RE: Why does the firmware memory region have no
permissions?
Hi Abner,

-----Original Message-----
From: Chang, Abner (HPS SW/FW Technologist)
[off-list ref]
Sent: 15 May 2021 11:47
To: Anup Patel <redacted>; Daniel Schaefer
[off-list ref]
Cc: opensbi at lists.infradead.org
Subject: RE: Why does the firmware memory region have no
permissions?

-----Original Message-----
From: Anup Patel [mailto:Anup.Patel at wdc.com]
Sent: Friday, May 14, 2021 7:58 PM
To: Daniel Schaefer <redacted>
Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
Technologist)
[off-list ref]
Subject: RE: Why does the firmware memory region have no
permissions?

-----Original Message-----
From: Anup Patel
Sent: 14 May 2021 17:22
To: Daniel Schaefer <redacted>
Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
Technologist) [off-list ref]
Subject: RE: Why does the firmware memory region have no
permissions?

-----Original Message-----
From: opensbi <redacted> On
Behalf
Of
Daniel Schaefer
Sent: 13 May 2021 10:26
To: Anup Patel <redacted>
Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
Technologist) [off-list ref]
Subject: Why does the firmware memory region have no
permissions?
Whoops, put CC as subject...

On 5/12/21 6:20 PM, Daniel Schaefer wrote:
Hi Anup,

I'm in the process of upgrading EDKII to OpenSBI 0.9 and
using the Generic
Platform.
Previously we were doing sbi_init with M-Mode, adding our
SBI extension and then calling sbi_switch_mode to switch to S-
Mode.
Now sbi_init disallows initializing to M-Mode, so I'm
directly switching to S-Mode. It seems that even from
S-Mode I can register our SBI
extension with sbi_ecall_register_extension.
Is that correct?
The OpenSBI sources are meant to run only from M-mode so we
cannot
register SBI extension using sbi_ecall_register_extension().

The  sbi_switch_mode() is not stricter due to OpenSBI domain
support.
The sbi_hart_switch_mode() is fine. It's the sbi_domain_init()
which is enforcing next booting stage to be at lower privilege for
root
domain.
For time being, you can try removing checks on "dom->next_mode"
in sanitize_domain()
Hi Anup, I think we currently skip that check for moving on the
edk2 boot process. So do you have plan to remove this check? Or any
alternative?
I think it is unnecessary having this check on the next privilege mode.
That
should be at OEM discretion of which privilege mode to run their
next firmware stage based on the platform design?
This is an important check required by OpenSBI domain support so
that next booting stage cannot tamper with PMP configuration (and
other security configuration) done by OpenSBI.
I understand the importance of not giving any chance to tamper PMP
setting, however this could be the responsibility of the next boot phase
before OS.
OpenSBI as the early phase boot firmware should be generally provide
SBIs to platform variants, and have the flexibility to hand off to
either M-mode or S-mode firmware (Actually I don't think OpenSBI
should
handle this).
Platform code is provided by OEM/vendor, OpenSBI should allow it if
platform code says I would like to run my next phase firmware in M-
mode.
We restrict the privilege phase for the next phase in OpenSBI also not
compliant with the UEFI spec which says UEFI RISC-V firmware could be
executed in either M-mode or S-mode. Some EFI driver may be loaded in
S- mode but provide the M-mode code such as management mode, the
Platform Runtime Mechanism or some other use cases. The next
firmware
has the responsibility to switch to S-mode when handoff to OS or
software if the platform design requires that (I remember we have the
simi  lar sentence in riscv-platform-spec). EDK2 code can't just
remove the check "dom->next_mode", we use OpenSBI without any
changes.

I am still worried about the custom SBI extension required by EDK2.
This will not work when running EDK2 inside Guest/VM because
Guest/VM boots in VS-mode and the SBI calls are provided by
hypervisors (KVM, Xvisor, etc). I think you should revisit EDK2
boot-flow to make it compatible with virtualization and OpenSBI
domains.
Ok, I will revisit this. Thanks for the reminder.
Hi Anup,
I have few questions regard to HSM support in opensbi,

- Is the purpose of invoking platform_domain_init at the end of sbi_init() to
let platform code to register the domains through sbi_domain_register()?
Yes, domains need to be populated as late as possible so that domains
are switched only after all initialization is completed.

- What is the reason that each domain is requested to have the memory
region of ROOT_FW_REGION?
The ROOT_FW_REGION protects the firmware itself. The fw_region is based
on fw_start and fw_size members of the "struct sbi_scratch".

- I think opensbi will have the implement of switching the next mode to
HSM
later?
Can you elaborate why you need this ?
Ah no I was just wonder how opensbi switch the next mode to HSM. You had the answer in below.

- How does opensbi loads the hypervisor in HSM?
When H-extension is available the next mode is automatically HS-mode
(i.e. S-mode with virt=off).

You still did not share how you will make EDK2 boot flow work for
VS-modes because hypervisor will start Guest/VM directly in VS-mode
and M-mode components of EDK2 can't run inside Guest/VM
I don't have the full picture of EDK2 boot flow for HSM yet. I am still thinking how the Management Mode work on HSM especially to the multiple type1 hypervisors run on the each domain. Also, the platform errors or RAS errors on server platform has to deliver the error event to the corresponding domains. The idea as I mentioned earlier, EDK2 FW is not necessarily  to be executed as a VS entity. EDK2 FW is executed when processor power on and it uses opensbi as a library to initial the basic platform (vendor) and opensbi initialization, then edk2 FW run through PEI/DXE for the OEM platform and proprietary features initialization. EDK2 still can jump to opensbi to run the domain initialization at the last boot stage, says BDS,  and then switch to HSM. We have to consider those server features such as critical platform error handling, event logging, FW<->BMC communication, Remote FW configuration through Redfish beyond the HSM, or some of above drivers can run in HSM before hypervisor is launched, I am not sure yet.
SBI FW extension shouldn't be the problem because HSM hypervisor can still bypass the sbi invocations from VS entity to M-mode if the sbi function number is in the firmware range, right? e.g. SBI FW extension can still provide the management mode interface to (V)S mode entity.

Abner

Regards,
Anup

Regards,
Abner

Regards,
Abner
Regards,
Anup

Thanks and regards,
Abner

Next booting stage has to run from lower privilege mode
(S-mode or
U-
mode) otherwise OpenSBI cannot protect itself from next
booting stage if it starts in M-mode.

However, sbi_init when directly initializing to S-Mode
checks that the
start_address is executable.
So I'm wondering why the FW region isn't set as executable
in
OpenSBI?
How do other FWs like U-Boot get around this?

https://github.com/riscv/opensbi/commit/b1678af210dc4b4e6d586d6d966
1
7
e
9641618994#diff-
6e8e352a8a90ba5a7adbb58a806ed9b6404c2c67db416332f9c05a
6b322eecd6R346

If I try to set my own regions by adding
.domains_root_regions I get another error because OpenSBI
checks that I have a region that is the same as the FW
region added by OpenSBI. If I duplicate the FW region and
mark the first one as executable I can pass the executable
check and also the check that there's an
FW
region.
Additionally we have to manually call pmp_set in our
custom platform to make the FW region RWX.

That seems like a workaround, however. Do you have any
suggestion to
properly fix it?
I'm sure we're misunderstand something.
I suggest two things:
1) Register your custom SBI extension from M-mode only before
switching to S-mode
2) Make sure that fw_start and fw_size set in the sbi_scratch
for each HART only point to the M-mode code and data.
Preferably have S-mode code and data not linked in the same
binary as M-mode code
and
data.

For context: We're writing the start addr and size of our
FW image into the scratch space before OpenSBI is initialized.
Therefore we're expecting it to set the PMP settings correctly.

Please check out my workaround commit:
https://github.com/riscv/riscv-edk2-
platforms/commit/a5ac63096ca
5da7
95
042baf650170643fe219cab

Thanks,
Daniel
Regards
Anup
Regards,
Anup
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