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Tue, 04 Aug 2026 22:58:32 -0700 (PDT) Received: from va-HP-Pavilion-Desktop-595-p0xxx.mshome.net ([193.0.148.216]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6a145de6b07sm1305396a12.16.2026.08.04.22.58.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Aug 2026 22:58:32 -0700 (PDT) From: Valery Borovsky To: seanjc@google.com, pbonzini@redhat.com Cc: kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, shuah@kernel.org, linux-kernel@vger.kernel.org, Valery Borovsky Subject: [PATCH] KVM: selftests: verify toggling KVM_MEM_GUEST_MEMFD on an existing slot is rejected Date: Wed, 5 Aug 2026 08:58:30 +0300 Message-ID: <20260805055830.740175-1-vebohr@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit set_memory_region_test covers creating a private memslot and rejecting overlapping private regions, but nothing exercises a FLAGS_ONLY update that toggles KVM_MEM_GUEST_MEMFD on a slot that already exists. Add test_toggle_private_memory_region() to close that gap. It asserts both directions are rejected with EINVAL: 1. clearing KVM_MEM_GUEST_MEMFD on a private slot; 2. setting KVM_MEM_GUEST_MEMFD on a slot created without it. Both are enforced by the flags mask in kvm_set_memory_region(): (mem->flags ^ old->flags) & (KVM_MEM_READONLY | KVM_MEM_GUEST_MEMFD) which gained KVM_MEM_GUEST_MEMFD in commit 9935df5333aa ("KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot"). Before that commit, direction 1 freed the old slot without calling kvm_gmem_unbind(), so closing the guest_memfd afterwards wrote to freed memory; the fix commit records the resulting KASAN slab-use-after-free in kvm_gmem_release(). The test runs only when KVM_X86_SW_PROTECTED_VM is available, alongside the existing private-memslot tests. Signed-off-by: Valery Borovsky --- Built and run on x86_64 against a 7.0 kernel; the new subtest passes. .../selftests/kvm/set_memory_region_test.c | 45 +++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c index a152ab65c657..8fb2e7a96f6c 100644 --- a/tools/testing/selftests/kvm/set_memory_region_test.c +++ b/tools/testing/selftests/kvm/set_memory_region_test.c @@ -500,6 +500,50 @@ static void test_add_private_memory_region(void) kvm_vm_free(vm); } +static void test_toggle_private_memory_region(void) +{ + struct kvm_vm *vm; + int memfd, r; + + pr_info("Testing that toggling KVM_MEM_GUEST_MEMFD on existing slot is rejected\n"); + + vm = vm_create_barebones_type(KVM_X86_SW_PROTECTED_VM); + memfd = vm_create_guest_memfd(vm, MEM_REGION_SIZE, 0); + + /* Create a private slot. */ + vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD, + MEM_REGION_GPA, MEM_REGION_SIZE, + 0, memfd, 0); + + /* + * Attempt a FLAGS_ONLY update that clears KVM_MEM_GUEST_MEMFD. + * Must fail with EINVAL. Before commit 9935df5333aa this caused + * a slab-use-after-free in kvm_gmem_release() because the old slot + * was freed without calling kvm_gmem_unbind(). + */ + r = __vm_set_user_memory_region2(vm, MEM_REGION_SLOT, 0, + MEM_REGION_GPA, MEM_REGION_SIZE, + 0, memfd, 0); + TEST_ASSERT(r == -1 && errno == EINVAL, + "Clearing KVM_MEM_GUEST_MEMFD should have failed with EINVAL, got r=%d errno=%d", r, errno); + + /* + * Symmetrically, attempting to set KVM_MEM_GUEST_MEMFD on a slot + * that was created without it must also be rejected. + */ + vm_set_user_memory_region(vm, MEM_REGION_SLOT + 1, 0, + MEM_REGION_GPA * 2, MEM_REGION_SIZE, NULL); + r = __vm_set_user_memory_region2(vm, MEM_REGION_SLOT + 1, + KVM_MEM_GUEST_MEMFD, + MEM_REGION_GPA * 2, MEM_REGION_SIZE, + 0, memfd, 0); + TEST_ASSERT(r == -1 && errno == EINVAL, + "Setting KVM_MEM_GUEST_MEMFD should have failed with EINVAL, got r=%d errno=%d", r, errno); + + close(memfd); + kvm_vm_free(vm); +} + static void test_add_overlapping_private_memory_regions(void) { struct kvm_vm *vm; @@ -645,6 +689,7 @@ int main(int argc, char *argv[]) (kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM))) { test_add_private_memory_region(); test_add_overlapping_private_memory_regions(); + test_toggle_private_memory_region(); } else { pr_info("Skipping tests for KVM_MEM_GUEST_MEMFD memory regions\n"); } -- 2.53.0