Re: [PATCH v5.5 02/30] KVM: Disallow user memslot with size that exceeds "unsigned long"

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Anup Patel <anup.patel@wdc.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	kvm@vger.kernel.org, David Hildenbrand <david@redhat.com>,
	linux-kernel@vger.kernel.org, Paul Mackerras <paulus@ozlabs.org>,
	Atish Patra <atish.patra@wdc.com>,
	Ben Gardon <bgardon@google.com>,
	linux-riscv@lists.infradead.org,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	kvmarm@lists.cs.columbia.edu,
	Janosch Frank <frankja@linux.ibm.com>,
	Marc Zyngier <maz@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	kvm-ppc@vger.kernel.org, Paul Walmsley <paul.walmsley@sifive.com>,
	linux-arm-kernel@lists.infradead.org,
	Jim Mattson <jmattson@google.com>,
	Cornelia Huck <cohuck@redhat.com>,
	linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v5.5 02/30] KVM: Disallow user memslot with size that exceeds "unsigned long"
Date: Tue, 9 Nov 2021 01:38:02 +0100	[thread overview]
Message-ID: <2f451590-bf89-d447-d92a-fe9f3f41ca74@oracle.com> (raw)
In-Reply-To: <20211104002531.1176691-3-seanjc@google.com>

On 04.11.2021 01:25, Sean Christopherson wrote:
> Reject userspace memslots whose size exceeds the storage capacity of an
> "unsigned long".  KVM's uAPI takes the size as u64 to support large slots
> on 64-bit hosts, but does not account for the size being truncated on
> 32-bit hosts in various flows.  The access_ok() check on the userspace
> virtual address in particular casts the size to "unsigned long" and will
> check the wrong number of bytes.
> 
> KVM doesn't actually support slots whose size doesn't fit in an "unsigned
> long", e.g. KVM's internal kvm_memory_slot.npages is an "unsigned long",
> not a "u64", and misc arch specific code follows that behavior.
> 
> Fixes: fa3d315a4ce2 ("KVM: Validate userspace_addr of memslot when registered")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   virt/kvm/kvm_main.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 99e69375c4c9..83287730389f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1689,7 +1689,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	id = (u16)mem->slot;
>   
>   	/* General sanity checks */
> -	if (mem->memory_size & (PAGE_SIZE - 1))
> +	if ((mem->memory_size & (PAGE_SIZE - 1)) ||
> +	    (mem->memory_size != (unsigned long)mem->memory_size))
>   		return -EINVAL;
>   	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
>   		return -EINVAL;
> 

Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
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