diff mbox series

[PATCHv12,06/16] KVM: Serialize tagged address check against tagging enabling

Message ID 20221109165140.9137-7-kirill.shutemov@linux.intel.com
State New
Headers
Series Linear Address Masking enabling |

Commit Message

Kirill A. Shutemov Nov. 9, 2022, 4:51 p.m. UTC 
  KVM forbids usage of tagged userspace addresses for memslots. It is done
by checking if the address stays the same after untagging.

It is works fine for ARM TBI, but it the check gets racy for LAM. TBI
enabling happens per-thread, so nobody can enable tagging for the thread
while the memslot gets added.

LAM gets enabled per-process. If it gets enabled after the
untagged_addr() check, but before access_ok() check the kernel can
wrongly allow tagged userspace_addr.

Use mmap lock to protect against parallel LAM enabling.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Marc Zyngier <maz@kernel.org>
---
 virt/kvm/kvm_main.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d2139906ff91..8399aae16e83 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1943,12 +1943,22 @@  int __kvm_set_memory_region(struct kvm *kvm,
 		return -EINVAL;
 	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
 		return -EINVAL;
+
+	/* Serialize against tagging enabling */
+	if (mmap_read_lock_killable(kvm->mm))
+		return -EINTR;
+
 	/* We can read the guest memory with __xxx_user() later on. */
 	if ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
 	    (mem->userspace_addr != untagged_addr(kvm->mm, mem->userspace_addr)) ||
 	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
-			mem->memory_size))
+			mem->memory_size)) {
+		mmap_read_unlock(kvm->mm);
 		return -EINVAL;
+	}
+
+	mmap_read_unlock(kvm->mm);
+
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
 		return -EINVAL;
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)