linux-kernel - Re: [PATCH 03/12] KVM: arm64: Block unsafe FF-A calls from the host

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Message-ID: <20230418124147.GA32435@willie-the-truck>
Date:   Tue, 18 Apr 2023 13:41:49 +0100
From:   Will Deacon <will@...nel.org>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     Quentin Perret <qperret@...gle.com>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Andrew Walbran <qwandor@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 03/12] KVM: arm64: Block unsafe FF-A calls from the host

On Wed, Nov 16, 2022 at 05:40:48PM +0000, Oliver Upton wrote:
> On Wed, Nov 16, 2022 at 05:03:26PM +0000, Quentin Perret wrote:
> > From: Will Deacon <will@...nel.org>
> > 
> > When KVM is initialised in protected mode, we must take care to filter
> > certain FFA calls from the host kernel so that the integrity of guest
> > and hypervisor memory is maintained and is not made available to the
> > secure world.
> > 
> > As a first step, intercept and block all memory-related FF-A SMC calls
> > from the host to EL3. This puts the framework in place for handling them
> > properly.
> 
> Shouldn't FFA_FEATURES interception actually precede this patch? At this
> point in the series we're outright lying about the supported features to
> the host.

FF-A is in a pretty sorry state after this patch as we block all the memory
transactions, but I take your point that we should be consistent and not
advertise the features that we're blocking.

I'll return FFA_RET_NOT_SUPPORTED for all FFA_FEATURES calls until the
interception patch comes in later and does something smarter.

Will