Re: [edk2-devel] [PATCH 0/4] OvmfPkg: Add VirtHstiDxe driver

["Gerd Hoffmann" <kraxel@redhat.com>]

On Wed, Apr 17, 2024 at 01:20:57PM +0000, Yao, Jiewen wrote:
> That is good start. The SMRAM lock and Flash lock seem good to me.
> 
> Comment:
> 1) Do we really need to add "Q35" for the policy?
> #define VIRT_HSTI_BYTE0_Q35_SMM_SMRAM_LOCK         BIT0
> #define VIRT_HSTI_BYTE0_Q35_SMM_SECURE_VARS_FLASH  BIT1
> 
> I feel we had better remove it, since SMM_SMRAM_LOCK and SMM_SECURE_VARS_FLASH are common features for almost all X86 platforms.

Well, SMM mode is supported for the qemu 'q35' machine type only, the
'pc' machine type doesn't provide enough memory for SMM.  Which why I've
added 'Q35' to the name.

The SMM_SMRAM_LOCK test actually is q35-specific because the control
registers are chipset specific.  But, yes, the concept is not q35
specific.

I can drop 'Q35' if you prefer it that way.

> 2) Would you please let me know what "READONLY_CODE_FLASH" really means?
> 
> #define VIRT_HSTI_BYTE0_Q35_SMM_SECURE_VARS_FLASH  BIT1
> #define VIRT_HSTI_BYTE0_READONLY_CODE_FLASH        BIT2
> 
> Does READONLY_CODE_FLASH mean NO write to flash even in SMM mode?
> Or does it just mean NO write in normal operation mode, but still writable in SMM mode?

With qemu being configured properly flash behavior should be this:

                               |  OVMF_CODE.fd  |  OVMF_VARS.fd
-------------------------------+----------------+----------------
SMM_REQUIRE=TRUE, SMM mode     |  read-only     |  writable
SMM_REQUIRE=TRUE, normal mode  |  read-only (1) |  read-only (2)
SMM_REQUIRE=FALSE              |  read-only (3) |  writable

VIRT_HSTI_BYTE0_READONLY_CODE_FLASH will verify (1) + (3).
VIRT_HSTI_BYTE0_Q35_SMM_SECURE_VARS_FLASH will verify (2).

(probably a good idea to add that as comment to the patches).

take care,
  Gerd



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