Re: [PATCH v2 9/9] mmc: sdhci-msm: add Inline Crypto Engine support

[Satya Tangirala <satyat@google.com>]

On Sat, Dec 05, 2020 at 11:43:21AM -0800, Eric Biggers wrote:
> On Sat, Dec 05, 2020 at 12:09:16PM +0000, Satya Tangirala wrote:
> > > +static void sdhci_msm_ice_enable(struct sdhci_msm_host *msm_host)
> > > +{
> > > +	if (!(msm_host->mmc->caps2 & MMC_CAP2_CRYPTO))
> > > +		return;
> > > +	sdhci_msm_ice_low_power_mode_enable(msm_host);
> > > +	sdhci_msm_ice_optimization_enable(msm_host);
> > > +	sdhci_msm_ice_wait_bist_status(msm_host);
> > If sdhci_msm_ice_wait_bist_status() fails, should we really ignore the
> > error and continue en/decrypting with ICE? I'm not sure what the BIST
> > failing might really mean, but if it means it's possible that the ICE
> > en/decrypts incorrectly it would be bad to continue to use it.....
> 
> The "built-in self-test" that the ICE hardware does seems to be a FIPS
> compliance thing which never actually fails in practice.
> 
> If it does fail, then according to
> https://csrc.nist.gov/CSRC/media/projects/cryptographic-module-validation-program/documents/security-policies/140sp2588.pdf
> (which is the closest thing I have to any documentation for ICE, other than the
> eMMC standard), then the hardware itself will reject any crypto requests.  So
> rejecting them in software too should be redundant.
> 
> It's also worth noting that just because a hardware-level self-test passes
> doesn't mean that the actual end-to-end storage encryption is working correctly.
> To verify that you need to run something like Android's
> vts_kernel_encryption_test, or the ciphertext verification tests in xfstests.
> The hardware itself is really the wrong place to be testing the encryption.
> 
> It would be possible to add some code that sets a flag in the cqhci_host if the
> ICE hardware test fails, and make cqhci_request() fail any crypto-enabled
> requests if that flag is set.  It just doesn't seem necessary, and I think we
> should error on the side of less complexity for now.
> 
> What I was actually worried about is what happens if ICE needs to be used but
> its self-test is still running, so it doesn't want to accept requests yet.  I'm
> not sure that's really a thing or not (one might hope the MMC host doesn't say
> it's done resetting until the ICE tests are done), but that's why I left in the
> code that waits for the tests to complete, which the downstream driver had.
> 
> Neeraj and Barani, if you have any additional insight or suggestions on this, or
> know of anything I may be overlooking, that would be greatly appreciated.
> 
> Otherwise I just plan to add a comment that summarizes what I said above.
> 
Sure, sounds good to me :).
> > > @@ -2531,12 +2785,15 @@ static __maybe_unused int sdhci_msm_runtime_resume(struct device *dev)
> > >  	 * Whenever core-clock is gated dynamically, it's needed to
> > >  	 * restore the SDR DLL settings when the clock is ungated.
> > >  	 */
> > > -	if (msm_host->restore_dll_config && msm_host->clk_rate)
> > > +	if (msm_host->restore_dll_config && msm_host->clk_rate) {
> > >  		ret = sdhci_msm_restore_sdr_dll_config(host);
> > > +		if (ret)
> > > +			return ret;
> > > +	}
> > >  
> > >  	dev_pm_opp_set_rate(dev, msm_host->clk_rate);
> > >  
> > > -	return ret;
> > > +	return sdhci_msm_ice_resume(msm_host);
> > >  }
> > Doesn't this modify existing behaviour if
> > sdhci_msm_restore_sdr_dll_config() returns a non-zero value? Previously,
> > dev_pm_opp_set_rate() would always be called regardless of ret, but now
> > it's not called on non-zero ret value.
> 
> Yes but I don't think it matters.  IIUC, if a device's ->runtime_resume()
> callback fails, then Linux's runtime power management framework keeps the device
> in an error state and doesn't consider it to be resumed.
> 
> So if resuming a device involves N different things, and one of them fails, I
> don't think we need to worry about trying to still do the other N-1 things; we
> can just return an error on the first failure.
>
Ah, alright. Once you do add the comment you mentioned above, please
feel free to add
Reviewed-by: Satya Tangirala <satyat@google.com>
> - Eric