linux-kernel - Re: [PATCH] KVM: arm64: Fix uninitialized memcache pointer in user_mem

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Message-ID: <aBnmM7DSonZr_VHC@google.com>
Date: Tue, 6 May 2025 11:36:35 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: Sebastian Ott <sebott@...hat.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Quentin Perret <qperret@...gle.com>, Fuad Tabba <tabba@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix uninitialized memcache pointer in
 user_mem_abort()

On Mon, May 05, 2025 at 07:31:48PM +0200, Sebastian Ott wrote:
> Commit fce886a60207 ("KVM: arm64: Plumb the pKVM MMU in KVM") made the
> initialization of the local memcache variable in user_mem_abort()
> conditional, leaving a codepath where it is used uninitialized via
> kvm_pgtable_stage2_map().
> 
> This can fail on any path that requires a stage-2 allocation
> without transition via a permission fault or dirty logging.
> 
> Fix this by making sure that memcache is always valid.
> 
> Fixes: fce886a60207 ("KVM: arm64: Plumb the pKVM MMU in KVM")
> Signed-off-by: Sebastian Ott <sebott@...hat.com>
> Reviewed-by: Marc Zyngier <maz@...nel.org>
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/kvmarm/3f5db4c7-ccce-fb95-595c-692fa7aad227@redhat.com/
> ---
>  arch/arm64/kvm/mmu.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 754f2fe0cc67..eeda92330ade 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1501,6 +1501,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  		return -EFAULT;
>  	}
>  
> +	if (!is_protected_kvm_enabled())
> +		memcache = &vcpu->arch.mmu_page_cache;
> +	else
> +		memcache = &vcpu->arch.pkvm_memcache;
> +
>  	/*
>  	 * Permission faults just need to update the existing leaf entry,
>  	 * and so normally don't require allocations from the memcache. The
> @@ -1510,13 +1515,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (!fault_is_perm || (logging_active && write_fault)) {
>  		int min_pages = kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu);
>  
> -		if (!is_protected_kvm_enabled()) {
> -			memcache = &vcpu->arch.mmu_page_cache;
> +		if (!is_protected_kvm_enabled())
>  			ret = kvm_mmu_topup_memory_cache(memcache, min_pages);
> -		} else {
> -			memcache = &vcpu->arch.pkvm_memcache;
> +		else
>  			ret = topup_hyp_memcache(memcache, min_pages);
> -		}
> +
>  		if (ret)
>  			return ret;
>  	}
> 
> base-commit: 92a09c47464d040866cf2b4cd052bc60555185fb
> -- 
> 2.49.0
> 
> 

For the pKVM part 

Reviewed-by: Vincent Donnefort <vdonnefort@...gle.com>

Thanks