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Message-ID: <863496e4yg.wl-maz@kernel.org>
Date: Mon, 01 Sep 2025 13:24:07 +0100
From: Marc Zyngier <maz@...nel.org>
To: James Clark <james.clark@...aro.org>
Cc: Yingchao Deng <yingchao.deng@....qualcomm.com>,
linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev,
linux-kernel@...r.kernel.org,
quic_yingdeng@...cinc.com,
jinlong.mao@....qualcomm.com,
tingwei.zhang@....qualcomm.com,
Oliver Upton <oliver.upton@...ux.dev>,
Joey Gouly <joey.gouly@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>,
Catalin Marinas
<catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH] KVM: arm64: Fix NULL pointer access issue
On Mon, 01 Sep 2025 11:36:11 +0100,
James Clark <james.clark@...aro.org> wrote:
>
>
>
> On 01/09/2025 11:01 am, Yingchao Deng wrote:
> > When linux is booted in EL1, macro "host_data_ptr()" is a wrapper that
> > resolves to "&per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)",
> > is_hyp_mode_available() return false during kvm_arm_init, the per-CPU base
> > pointer __kvm_nvhe_kvm_arm_hyp_percpu_base[cpu] remains uninitialized.
> > Consequently, any access via per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)
> > will result in a NULL pointer.
> >
> > Add is_kvm_arm_initialised() condition check to ensure that kvm_arm_init
> > completes all necessary initialization steps, including init_hyp_mode.
> >
> > Fixes: 054b88391bbe2 ("KVM: arm64: Support trace filtering for guests")
> > Signed-off-by: Yingchao Deng <yingchao.deng@....qualcomm.com>
> > ---
> > Add a check to prevent accessing uninitialized per-CPU data.
> > ---
> > arch/arm64/kvm/debug.c | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> > index 381382c19fe4741980c79b08bbdab6a1bcd825ad..add58056297293b4eb337028773b1b018ecc9d35 100644
> > --- a/arch/arm64/kvm/debug.c
> > +++ b/arch/arm64/kvm/debug.c
> > @@ -233,7 +233,7 @@ void kvm_debug_handle_oslar(struct kvm_vcpu *vcpu, u64 val)
> > void kvm_enable_trbe(void)
> > {
> > if (has_vhe() || is_protected_kvm_enabled() ||
> > - WARN_ON_ONCE(preemptible()))
> > + WARN_ON_ONCE(preemptible()) || !is_kvm_arm_initialised())
>
> Hi Yingchao,
>
> There shouldn't be a warning for this, at least for the case where
> it's not initialized and never will be. If you're never going to run a
> guest these functions can all skip, the same way for !has_vhe() etc.
It's not a warning. It's a bona-fide crash:
void kvm_enable_trbe(void)
{
if (has_vhe() || is_protected_kvm_enabled() ||
WARN_ON_ONCE(preemptible()))
return;
host_data_set_flag(TRBE_ENABLED); <--- Explodes here
}
So the write of the flag has to be skipped if KVM is available, even
if KVM is compiled in.
M.
--
Without deviation from the norm, progress is not possible.
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