lkml.org 
[lkml]   [2019]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] KVM: arm: remove excessive permission check in kvm arch prepare memory region
Date
From
On 2019-12-06 02:08, Jia He wrote:
> In kvm_arch_prepare_memory_region, arm kvm regards the memory region
> as
> writable if the flag has no KVM_MEM_READONLY, and the vm is readonly
> if
> !VM_WRITE.
>
> But there is common usage for setting kvm memory region as follows:
> e.g. qemu side (see the PROT_NONE flag)
> 1. mmap(NULL, size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> memory_region_init_ram_ptr()
> 2. re mmap the above area with read/write authority.
>
> Such example is used in virtio-fs qemu codes which hasn't been
> upstreamed
> [1]. But seems we can't forbid this example.
>
> Without this patch, it will cause an EPERM during
> kvm_set_memory_region()
> and cause qemu boot crash.
>
> As told by Ard, "the underlying assumption is incorrect, i.e., that
> the
> value of vm_flags at this point in time defines how the VMA is used
> during its lifetime. There may be other cases where a VMA is created
> with VM_READ vm_flags that are changed to VM_READ|VM_WRITE later, and
> we are currently rejecting this use case as well."
>
> [1]
>
> https://gitlab.com/virtio-fs/qemu/blob/5a356e/hw/virtio/vhost-user-fs.c#L488
>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
> virt/kvm/arm/mmu.c | 9 ---------
> 1 file changed, 9 deletions(-)
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 38b4c910b6c3..a48994af70b8 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -2301,15 +2301,6 @@ int kvm_arch_prepare_memory_region(struct kvm
> *kvm,
> if (!vma || vma->vm_start >= reg_end)
> break;
>
> - /*
> - * Mapping a read-only VMA is only allowed if the
> - * memory region is configured as read-only.
> - */
> - if (writable && !(vma->vm_flags & VM_WRITE)) {
> - ret = -EPERM;
> - break;
> - }
> -
> /*
> * Take the intersection of this VMA with the memory region
> */

Applied, thanks.

M.
--
Jazz is not dead. It just smells funny...

\
 
 \ /
  Last update: 2019-12-06 12:44    [W:0.037 / U:2.688 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site