linux-kernel - Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging

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: <ZrOfB8bOdSJVcWFr@arm.com>
Date: Wed, 7 Aug 2024 17:21:27 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Anup Patel <anup@...infault.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	David Matlack <dmatlack@...gle.com>,
	David Stevens <stevensd@...omium.org>
Subject: Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest
 memory while KVM is dirty logging

On Fri, Jul 26, 2024 at 04:51:11PM -0700, Sean Christopherson wrote:
> Disallow copying MTE tags to guest memory while KVM is dirty logging, as
> writing guest memory without marking the gfn as dirty in the memslot could
> result in userspace failing to migrate the updated page.  Ideally (maybe?),
> KVM would simply mark the gfn as dirty, but there is no vCPU to work with,
> and presumably the only use case for copy MTE tags _to_ the guest is when
> restoring state on the target.
> 
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/arm64/kvm/guest.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index e1f0ff08836a..962f985977c2 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1045,6 +1045,11 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  
>  	mutex_lock(&kvm->slots_lock);
>  
> +	if (write && atomic_read(&kvm->nr_memslots_dirty_logging)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}

There are ways to actually log the page dirtying but I don't think
it's worth it. AFAICT, reading the tags still works and that's what's
used during migration (on the VM where dirty tracking takes place).

Reviewed-by: Catalin Marinas <catalin.marinas@....com>