Re: [PATCH] KVM: arm64: Ensure I-cache isolation between vcpus of a same VM

From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	kernel-team@android.com, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>
Subject: Re: [PATCH] KVM: arm64: Ensure I-cache isolation between vcpus of a same VM
Date: Tue, 9 Mar 2021 14:38:42 +0000	[thread overview]
Message-ID: <20210309143841.GA32754@arm.com> (raw)
In-Reply-To: <20210309132645.GA28297@willie-the-truck>

On Tue, Mar 09, 2021 at 01:26:46PM +0000, Will Deacon wrote:
> On Wed, Mar 03, 2021 at 04:45:05PM +0000, Marc Zyngier wrote:
> > It recently became apparent that the ARMv8 architecture has interesting
> > rules regarding attributes being used when fetching instructions
> > if the MMU is off at Stage-1.
> > 
> > In this situation, the CPU is allowed to fetch from the PoC and
> > allocate into the I-cache (unless the memory is mapped with
> > the XN attribute at Stage-2).
> > 
> > If we transpose this to vcpus sharing a single physical CPU,
> > it is possible for a vcpu running with its MMU off to influence
> > another vcpu running with its MMU on, as the latter is expected to
> > fetch from the PoU (and self-patching code doesn't flush below that
> > level).
> > 
> > In order to solve this, reuse the vcpu-private TLB invalidation
> > code to apply the same policy to the I-cache, nuking it every time
> > the vcpu runs on a physical CPU that ran another vcpu of the same
> > VM in the past.
> > 
> > This involve renaming __kvm_tlb_flush_local_vmid() to
> > __kvm_flush_cpu_context(), and inserting a local i-cache invalidation
> > there.
> > 
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/include/asm/kvm_asm.h   | 4 ++--
> >  arch/arm64/kvm/arm.c               | 7 ++++++-
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 6 +++---
> >  arch/arm64/kvm/hyp/nvhe/tlb.c      | 3 ++-
> >  arch/arm64/kvm/hyp/vhe/tlb.c       | 3 ++-
> >  5 files changed, 15 insertions(+), 8 deletions(-)
> 
> Since the FWB discussion doesn't affect the correctness of this patch:
> 
> Acked-by: Will Deacon <will@kernel.org>

I agree. We can optimise it later for FWB.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>