Why does the firmware memory region have no permissions?

Wed Jun 2 08:14:49 PDT 2021

> -----Original Message-----
> From: Chang, Abner (HPS SW/FW Technologist) <abner.chang at hpe.com>
> Sent: 02 June 2021 20:19
> To: Chang, Abner (HPS SW/FW Technologist) <abner.chang at hpe.com>; Anup
> Patel <Anup.Patel at wdc.com>; Daniel Schaefer <daniel at danielschaefer.me>
> 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 <Anup.Patel at wdc.com>; Daniel Schaefer
> > <daniel at danielschaefer.me>
> > 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) <abner.chang at hpe.com>;
> > Daniel
> > > Schaefer <daniel at danielschaefer.me>
> > > 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)
> > <abner.chang at hpe.com>
> > > > Sent: 15 May 2021 11:47
> > > > To: Anup Patel <Anup.Patel at wdc.com>; Daniel Schaefer
> > > > <daniel at danielschaefer.me>
> > > > 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 <daniel at danielschaefer.me>
> > > > > Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
> > Technologist)
> > > > > <abner.chang at hpe.com>
> > > > > 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 <daniel at danielschaefer.me>
> > > > > > Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
> > > > > > Technologist) <abner.chang at hpe.com>
> > > > > > Subject: RE: Why does the firmware memory region have no
> > > > permissions?
> > > > > >
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: opensbi <opensbi-bounces at lists.infradead.org> On
> > > > > > > Behalf
> > Of
> > > > > > > Daniel Schaefer
> > > > > > > Sent: 13 May 2021 10:26
> > > > > > > To: Anup Patel <Anup.Patel at wdc.com>
> > > > > > > Cc: opensbi at lists.infradead.org; Chang, Abner (HPS SW/FW
> > > > > > > Technologist) <abner.chang at hpe.com>
> > > > > > > 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 ?

> - 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

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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