From ab1ef34416a65ba11f66ae6435fcf0251cb46fd4 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 7 Dec 2021 19:30:06 +0000 Subject: [PATCH] KVM: selftests: Add test to verify TRIPLE_FAULT on invalid L2 guest state Add a selftest to attempt to enter L2 with invalid guests state by exiting to userspace via I/O from L2, and then using KVM_SET_SREGS to set invalid guest state (marking TR unusable is arbitrary chosen for its relative simplicity). This is a regression test for a bug introduced by commit c8607e4a086f ("KVM: x86: nVMX: don't fail nested VM entry on invalid guest state if !from_vmentry"), which incorrectly set vmx->fail=true when L2 had invalid guest state and ultimately triggered a WARN due to nested_vmx_vmexit() seeing vmx->fail==true while attempting to synthesize a nested VM-Exit. The is also a functional test to verify that KVM sythesizes TRIPLE_FAULT for L2, which is somewhat arbitrary behavior, instead of emulating L2. KVM should never emulate L2 due to invalid guest state, as it's architecturally impossible for L1 to run an L2 guest with invalid state as nested VM-Enter should always fail, i.e. L1 needs to do the emulation. Stuffing state via KVM ioctl() is a non-architctural, out-of-band case, hence the TRIPLE_FAULT being rather arbitrary. Signed-off-by: Sean Christopherson Message-Id: <20211207193006.120997-5-seanjc@google.com> Reviewed-by: Maxim Levitsky Signed-off-by: Paolo Bonzini --- tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile | 1 + .../kvm/x86_64/vmx_invalid_nested_guest_state.c | 105 +++++++++++++++++++++ 3 files changed, 107 insertions(+) create mode 100644 tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore index 00814c0..3cb5ac5 100644 --- a/tools/testing/selftests/kvm/.gitignore +++ b/tools/testing/selftests/kvm/.gitignore @@ -35,6 +35,7 @@ /x86_64/vmx_apic_access_test /x86_64/vmx_close_while_nested_test /x86_64/vmx_dirty_log_test +/x86_64/vmx_invalid_nested_guest_state /x86_64/vmx_preemption_timer_test /x86_64/vmx_set_nested_state_test /x86_64/vmx_tsc_adjust_test diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index f307c9f..17342b5 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -64,6 +64,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/userspace_msr_exit_test TEST_GEN_PROGS_x86_64 += x86_64/vmx_apic_access_test TEST_GEN_PROGS_x86_64 += x86_64/vmx_close_while_nested_test TEST_GEN_PROGS_x86_64 += x86_64/vmx_dirty_log_test +TEST_GEN_PROGS_x86_64 += x86_64/vmx_invalid_nested_guest_state TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test TEST_GEN_PROGS_x86_64 += x86_64/vmx_nested_tsc_scaling_test diff --git a/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c b/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c new file mode 100644 index 0000000..489fbed --- /dev/null +++ b/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c @@ -0,0 +1,105 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include "test_util.h" +#include "kvm_util.h" +#include "processor.h" +#include "vmx.h" + +#include +#include + +#include "kselftest.h" + +#define VCPU_ID 0 +#define ARBITRARY_IO_PORT 0x2000 + +static struct kvm_vm *vm; + +static void l2_guest_code(void) +{ + /* + * Generate an exit to L0 userspace, i.e. main(), via I/O to an + * arbitrary port. + */ + asm volatile("inb %%dx, %%al" + : : [port] "d" (ARBITRARY_IO_PORT) : "rax"); +} + +static void l1_guest_code(struct vmx_pages *vmx_pages) +{ +#define L2_GUEST_STACK_SIZE 64 + unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE]; + + GUEST_ASSERT(prepare_for_vmx_operation(vmx_pages)); + GUEST_ASSERT(load_vmcs(vmx_pages)); + + /* Prepare the VMCS for L2 execution. */ + prepare_vmcs(vmx_pages, l2_guest_code, + &l2_guest_stack[L2_GUEST_STACK_SIZE]); + + /* + * L2 must be run without unrestricted guest, verify that the selftests + * library hasn't enabled it. Because KVM selftests jump directly to + * 64-bit mode, unrestricted guest support isn't required. + */ + GUEST_ASSERT(!(vmreadz(CPU_BASED_VM_EXEC_CONTROL) & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS) || + !(vmreadz(SECONDARY_VM_EXEC_CONTROL) & SECONDARY_EXEC_UNRESTRICTED_GUEST)); + + GUEST_ASSERT(!vmlaunch()); + + /* L2 should triple fault after main() stuffs invalid guest state. */ + GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_TRIPLE_FAULT); + GUEST_DONE(); +} + +int main(int argc, char *argv[]) +{ + vm_vaddr_t vmx_pages_gva; + struct kvm_sregs sregs; + struct kvm_run *run; + struct ucall uc; + + nested_vmx_check_supported(); + + vm = vm_create_default(VCPU_ID, 0, (void *) l1_guest_code); + + /* Allocate VMX pages and shared descriptors (vmx_pages). */ + vcpu_alloc_vmx(vm, &vmx_pages_gva); + vcpu_args_set(vm, VCPU_ID, 1, vmx_pages_gva); + + vcpu_run(vm, VCPU_ID); + + run = vcpu_state(vm, VCPU_ID); + + /* + * The first exit to L0 userspace should be an I/O access from L2. + * Running L1 should launch L2 without triggering an exit to userspace. + */ + TEST_ASSERT(run->exit_reason == KVM_EXIT_IO, + "Expected KVM_EXIT_IO, got: %u (%s)\n", + run->exit_reason, exit_reason_str(run->exit_reason)); + + TEST_ASSERT(run->io.port == ARBITRARY_IO_PORT, + "Expected IN from port %d from L2, got port %d", + ARBITRARY_IO_PORT, run->io.port); + + /* + * Stuff invalid guest state for L2 by making TR unusuable. The next + * KVM_RUN should induce a TRIPLE_FAULT in L2 as KVM doesn't support + * emulating invalid guest state for L2. + */ + memset(&sregs, 0, sizeof(sregs)); + vcpu_sregs_get(vm, VCPU_ID, &sregs); + sregs.tr.unusable = 1; + vcpu_sregs_set(vm, VCPU_ID, &sregs); + + vcpu_run(vm, VCPU_ID); + + switch (get_ucall(vm, VCPU_ID, &uc)) { + case UCALL_DONE: + break; + case UCALL_ABORT: + TEST_FAIL("%s", (const char *)uc.args[0]); + default: + TEST_FAIL("Unexpected ucall: %lu", uc.cmd); + } +} -- 2.7.4