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

Christoffer Dall
2017-03-15T11:05:26Z

On Tue, Mar 14, 2017 at 02:52:33PM +0000, Suzuki K Poulose wrote:
> From: Marc Zyngier <marc.zyngier@arm.com>
>
> 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@linaro.org>
> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> Cc: Eric Auger <eric.auger@rehat.com>
> Cc: stable@vger.kernel.org # v3.18+
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> [ Handle dirty page logging failure case ]
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Christoffer Dall <cdall@linaro.org>

> ---
> 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
>