[RFC PATCH v2 32/37] KVM: selftests: Check fd/flags provided to mmap() when setting up memslot

[Ackerley Tng]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Check that a valid fd provided to mmap() must be accompanied by MAP_SHARED.

With an invalid fd (usually used for anonymous mappings), there are no
constraints on mmap() flags.

Add this check to make sure that when a guest_memfd is used as region->fd,
the flag provided to mmap() will include MAP_SHARED.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
[Rephrase assertion message.]
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 61adfd7e623c..aec7b24418ab 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1062,6 +1062,9 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 					     src_type == VM_MEM_SRC_SHARED_HUGETLB);
 	}
 
+	TEST_ASSERT(region->fd == -1 || backing_src_is_shared(src_type),
+		    "A valid fd provided to mmap() must be accompanied by MAP_SHARED.");
+
 	region->mmap_start = __kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE,
 					vm_mem_backing_src_alias(src_type)->flag,
 					region->fd, mmap_offset);
-- 
2.53.0.rc1.225.gd81095ad13-goog