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authorJia He <justin.he@arm.com>2019-12-06 10:08:02 +0800
committerMarc Zyngier <maz@kernel.org>2019-12-06 19:37:48 +0000
commit97418e968b01ba8e3ad41c38b42106c48bc19544 (patch)
treec34057345061cc89f73d299f83494eb0ca321299 /virt/kvm
parent54ad68b7776043a77c9bf0a67d49cd9cb261a8e7 (diff)
KVM: arm/arm64: Remove excessive permission check in kvm_arch_prepare_memory_region
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 Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Jia He <justin.he@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Reviewed-by: Christoffer Dall <christoffer.dall@arm.com> Link: https://lore.kernel.org/r/20191206020802.196108-1-justin.he@arm.com
Diffstat (limited to 'virt/kvm')
-rw-r--r--virt/kvm/arm/mmu.c9
1 files changed, 0 insertions, 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
@@ -2302,15 +2302,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
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
*/
vm_start = max(hva, vma->vm_start);