Re: [PATCH 2/3] kvm: arm/arm64: Take mmap_sem in kvm_arch_prepare_memory_region

[Christoffer Dall]

On Tue, Mar 14, 2017 at 02:52:33PM +0000, Suzuki K Poulose wrote:
> From: Marc Zyngier <marc.zyngier@xxxxxxx>
> 
> We don't hold the mmap_sem while searching for VMAs (via find_vma), in
> kvm_arch_prepare_memory_region, which can end up in expected failures.
> 
> Fixes: commit 8eef91239e57 ("arm/arm64: KVM: map MMIO regions at creation time")
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> Cc: Eric Auger <eric.auger@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v3.18+
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> [ Handle dirty page logging failure case ]
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Reviewed-by: Christoffer Dall <cdall@xxxxxxxxxx>

> ---
>  arch/arm/kvm/mmu.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index f2e2e0c..13b9c1f 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -1803,6 +1803,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	    (KVM_PHYS_SIZE >> PAGE_SHIFT))
>  		return -EFAULT;
>  
> +	down_read(&current->mm->mmap_sem);
>  	/*
>  	 * A memory region could potentially cover multiple VMAs, and any holes
>  	 * between them, so iterate over all of them to find out if we can map
> @@ -1846,8 +1847,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  			pa += vm_start - vma->vm_start;
>  
>  			/* IO region dirty page logging not allowed */
> -			if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES)
> -				return -EINVAL;
> +			if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> +				ret = -EINVAL;
> +				goto out;
> +			}
>  
>  			ret = kvm_phys_addr_ioremap(kvm, gpa, pa,
>  						    vm_end - vm_start,
> @@ -1859,7 +1862,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	} while (hva < reg_end);
>  
>  	if (change == KVM_MR_FLAGS_ONLY)
> -		return ret;
> +		goto out;
>  
>  	spin_lock(&kvm->mmu_lock);
>  	if (ret)
> @@ -1867,6 +1870,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	else
>  		stage2_flush_memslot(kvm, memslot);
>  	spin_unlock(&kvm->mmu_lock);
> +out:
> +	up_read(&current->mm->mmap_sem);
>  	return ret;
>  }
>  
> -- 
> 2.7.4
>