From 97418e968b01ba8e3ad41c38b42106c48bc19544 Mon Sep 17 00:00:00 2001 From: Jia He Date: Fri, 6 Dec 2019 10:08:02 +0800 Subject: 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 Signed-off-by: Jia He Signed-off-by: Marc Zyngier Reviewed-by: Christoffer Dall Link: https://lore.kernel.org/r/20191206020802.196108-1-justin.he@arm.com --- virt/kvm/arm/mmu.c | 9 --------- 1 file changed, 9 deletions(-) (limited to 'virt/kvm/arm/mmu.c') 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 */ -- cgit v1.2.3