linux-kernel - Re: [PATCH 2/2] KVM: arm64: Allow only the specified FF-A calls to be forwarded to TZ

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Message-ID: <ZgFgI0Ky2m4MUbw-@google.com>
Date: Mon, 25 Mar 2024 11:29:39 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: catalin.marinas@....com, james.morse@....com, jean-philippe@...aro.org,
	maz@...nel.org, qperret@...gle.com, qwandor@...gle.com,
	suzuki.poulose@....com, tabba@...gle.com, will@...nel.org,
	yuzenghui@...wei.com, kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-team@...roid.com
Subject: Re: [PATCH 2/2] KVM: arm64: Allow only the specified FF-A calls to
 be forwarded to TZ

On Fri, Mar 22, 2024 at 07:07:52PM -0700, Oliver Upton wrote:
> On Fri, Mar 22, 2024 at 12:43:03PM +0000, Sebastian Ene wrote:
> > The previous logic used a deny list to filter the FF-A calls. Because of
> > this, some of the calls escaped the check and they were forwarded by
> > default to Trustzone. (eg. FFA_MSG_SEND_DIRECT_REQ was denied but the 64
> > bit version of the call was not).
> > Modify the logic to use an allowlist and allow only the calls specified in
> > the filter function to be proxied to TZ from the hypervisor.

Hi Oliver,

> 
> I had discussed this with Will back when the feature was upstreamed and
> he said there's a lot of off-label calls that necessitate a denylist
> implementation. Has anything changed to give us confidence that we can
> be restrictive, at least on the FF-A range?
> 

I remember your proposal for having an allowlist instead. The current change makes
sense if we have https://lore.kernel.org/kvmarm/20240322124303.309423-1-sebastianene@google.com/
which opens the window for more FF-A calls to be forwarded to TZ.

Let me know if this clarifies, thanks
Seb

> -- 
> Thanks,
> Oliver