linux-kernel - Re: [PATCH] KVM: arm64: Validate input range for pKVM mem transitions

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Message-ID: <aM0p4UB3TNnsKcfC@google.com>
Date: Fri, 19 Sep 2025 11:01:05 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: maz@...nel.org, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, catalin.marinas@....com, will@...nel.org,
	qperret@...gle.com, sebastianene@...gle.com, keirf@...gle.com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH] KVM: arm64: Validate input range for pKVM mem transitions

On Thu, Sep 18, 2025 at 02:21:43PM -0700, Oliver Upton wrote:
> On Thu, Sep 18, 2025 at 07:00:49PM +0100, Vincent Donnefort wrote:
> > There's currently no verification for host issued ranges in most of the
> > pKVM memory transitions. The subsequent end boundary might therefore be
> > subject to overflow and could evade the later checks.
> > 
> > Close this loophole with an additional range_is_valid() check on a per
> > public function basis.
> > 
> > host_unshare_guest transition is already protected via
> > __check_host_shared_guest(), while assert_host_shared_guest() callers
> > are already ignoring host checks.
> > 
> > Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > index 8957734d6183..b156fb0bad0f 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > @@ -443,6 +443,11 @@ static bool range_is_memory(u64 start, u64 end)
> >  	return is_in_mem_range(end - 1, &r);
> >  }
> >  
> > +static bool range_is_valid(u64 start, u64 end)
> > +{
> > +	return start < end;
> > +}
> > +
> 
> I'm being unnecessarily pedantic but isn't something like [-2MiB, 0) a
> legal range if we had 64 bits of PA? Looks correct though so:

Apologies, I am not sure I see what you mean with this -2MiB range.

> 
> Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>
> 
> Thanks,
> Oliver