Re: [edk2-devel] [PATCH V1 1/1] OvmfPkg/QemuBootOrderLib: Measure the etc/boot-menu-wait

["sunceping" <cepingx.sun@intel.com>]

On Thursday, March 21, 2024 8:25 PM Gerd Hoffmann wrote:
> Well, just try to read them.  If present they can just be measured.
> If not present we can either skip them, or measure with an empty data 
> field to indicate it is not present.
My understanding :
If the fw_cfg is present,  it must be measured and consumed later.
Is this correct?

> > > > We propose below solution :
> > > >
> > > > Add a new API in QemuFwCfgLib,
> > > > RETURN_STATUS QemuFwCfgGetData(fw_cfg_name, *size, *value,
> > > FW_CFG_GET_DATA_FLAG flag).
> > >
> > > I'd suggest to *not* touch the existing interfaces for reading entries.
> > > Instead change the existing functions to first check the cache, in 
> > > case there is no cache entry go read from fw_cfg.
> > Actually we don't touch the existing interface for reading entries.
> > The API is newly added.
> 
> But then you have to find and update all callsites (or at least the 
> ones where we care about measurement).
In your solution,  if we cache all items that need to be measured,
we would have to add a new API (example: QemuFwCfgGetDataFromCache ())  to get the data from cache.

Then we also have to find and update all callsites.

Thanks
Ceping



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