linux-kernel - Re: [PATCH v8 33/43] arm64: RME: Hide KVM_CAP_READONLY

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bfddad3d-b15b-4122-a460-47489af11f24@arm.com>
Date: Tue, 20 May 2025 13:45:02 +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 v8 33/43] arm64: RME: Hide KVM_CAP_READONLY_MEM for realm
 guests

On 16/04/2025 14:41, Steven Price wrote:
> For protected memory read only isn't supported by the RMM. While it may
> be possible to support read only for unprotected memory, this isn't
> supported at the present time.
> 
> Note that this does mean that ROM (or flash) data cannot be emulated
> correctly by the VMM as the stage 2 mappings are either always
> read/write or are trapped as MMIO (so don't support operations where the
> syndrome information doesn't allow emulation, e.g. load/store pair).
> 
> This restriction can be lifted in the future by allowing the stage 2

minor nit: s/allowing the/allowing the unprotected/

> mappings to be made read only.
> 
> Signed-off-by: Steven Price <steven.price@....com>

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

> ---
> Changes since v7:
>   * Updated commit message to spell out the impact on ROM/flash
>     emulation.
> ---
>   arch/arm64/kvm/arm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 8060e25afbd0..4780e3af1bb9 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -340,7 +340,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_ONE_REG:
>   	case KVM_CAP_ARM_PSCI:
>   	case KVM_CAP_ARM_PSCI_0_2:
> -	case KVM_CAP_READONLY_MEM:
>   	case KVM_CAP_MP_STATE:
>   	case KVM_CAP_IMMEDIATE_EXIT:
>   	case KVM_CAP_VCPU_EVENTS:
> @@ -355,6 +354,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		r = 1;
>   		break;
>   	case KVM_CAP_COUNTER_OFFSET:
> +	case KVM_CAP_READONLY_MEM:
>   	case KVM_CAP_SET_GUEST_DEBUG:
>   		r = !kvm_is_realm(kvm);
>   		break;