linux-kernel - Re: [PATCH v5 31/43] arm64: rme: Prevent Device mappings for Realms

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Message-ID: <7ca207aa-4433-4e9b-8cd2-e025bb265796@arm.com>
Date: Fri, 18 Oct 2024 14:30:13 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Joey Gouly <joey.gouly@....com>, Alexandru Elisei
 <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
 Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v5 31/43] arm64: rme: Prevent Device mappings for Realms

On 04/10/2024 16:27, Steven Price wrote:
> Physical device assignment is not yet supported by the RMM, so it
> doesn't make much sense to allow device mappings within the realm.
> Prevent them when the guest is a realm.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>   arch/arm64/kvm/mmu.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 4f0403059c91..602c49eae90d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1142,6 +1142,10 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
>   	if (is_protected_kvm_enabled())
>   		return -EPERM;
>   
> +	/* We don't support mapping special pages into a Realm */
> +	if (kvm_is_realm(kvm))
> +		return -EINVAL;
> +

I believe this is not sufficient. This is only called for GICv2 today.
But we also need to check in  user_mem_abort() and only allow the
mapping if it targeting an unprotected IPA.

Something like:

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 26d550ad8393..e433bf8376f2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1710,6 +1710,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
phys_addr_t fault_ipa,
         if (exec_fault && device)
                 return -ENOEXEC;

+       if (device && kvm_gpa_from_fault(fault_ipa) != fault_ipa)
+               return -EINVAL;
+
         /*
          * Potentially reduce shadow S2 permissions to match the 
guest's own
          * S2. For exec faults, we'd only reach this point if the guest

Suzuki

>   	size += offset_in_page(guest_ipa);
>   	guest_ipa &= PAGE_MASK;
>