Re: [TF-A] [RFC] isolation between runtime BL33 services and OS

On Mon, Apr 20, 2020 at 03:37:23PM +0200, François Ozog wrote:

On Mon, 20 Apr 2020 at 15:27, Achin Gupta <[1]achin.gupta@arm.com> wrote:

 Hi Francois,
 On Mon, Apr 20, 2020 at 11:45:02AM +0000, Fran�ois Ozog via TF-A
 wrote:
 > Hi,
 >
 > I am trying to identify a mechanism to enforce a form of two-way
 > isolation between BL33 runtime services in OS, for instance:
 > - a pair of 2MB areas that could be RO by one entity and RW by the
 other
 > - an execute only BL33 2MB area?
 Stupid Q! Are you referring to isolation between EFI runtime
 services and the
 OS?
 It is not clear what you mean by BL33 runtime services?

Not a stupid Q. I concentrate effectively on EFI runtime but more generally this is the non-trusted firmware component that delivers runtime services to OS. (My flow is somewhat convoluted: TFA loads minimal Linux as BL33, Linux kexecs a UEFI reduced U-Boot (without drivers) which bootefi the distro).

Thanks! I see and IIUC, this is about two separately provisioned SW components that share an EL (EL1 in this case) at the same time in the same image. We want component A to have permission X on a memory region and component B to have permission Y on the same memory region. If so, then this would require a cooperation between the two components?

I might be still missing the obvious but I am wondering how a SW entity at a higher EL (Hypervisor in EL2 or TF-A in EL3) could create and enforce the separation between the two components. It would not have visibility of what is happening inside the EL at the very least.

cheers, Achin

 cheers,
 Achin
 >
 > This is similar to hypervisor except it only deals with memory, no
 > vCPU, no GIC virtualization...
 >
 > Could EL3 or EL2 install protective mappings ? BL33 could ask
 either
 > EL2 hypervisor or SecureMonitor to actually install them.
 >
 > Cordially,
 >
 > FF
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-- [uc?id=0BxTAygkus3RgQVhuNHMwUi1mYWc&amp;export=download] Fran�ois-Fr�d�ric Ozog | Director Linaro Edge & Fog Computing Group T: +33.67221.6485 [4]francois.ozog@linaro.org | Skype: ffozog

References

1. mailto:achin.gupta@arm.com
2. mailto:TF-A@lists.trustedfirmware.org
3. https://lists.trustedfirmware.org/mailman/listinfo/tf-a
4. mailto:francois.ozog@linaro.org

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.