Re: [RFC PATCH v5 16/29] KVM: selftests: TDX: Add TDX HLT exit test

[Binbin Wu <binbin.wu@linux.intel.com>]

On 12/13/2023 4:46 AM, Sagi Shahar wrote:
> The test verifies that the guest runs TDVMCALL<INSTRUCTION.HLT> and the
> guest vCPU enters to the halted state.
>
> Signed-off-by: Erdem Aktas <erdemaktas@google.com>
> Signed-off-by: Sagi Shahar <sagis@google.com>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Ryan Afranji <afranji@google.com>
> ---
>   .../selftests/kvm/include/x86_64/tdx/tdx.h    |  2 +
>   .../selftests/kvm/lib/x86_64/tdx/tdx.c        | 10 +++
>   .../selftests/kvm/x86_64/tdx_vm_tests.c       | 78 +++++++++++++++++++
>   3 files changed, 90 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/include/x86_64/tdx/tdx.h b/tools/testing/selftests/kvm/include/x86_64/tdx/tdx.h
> index 85ba6aab79a7..b18e39d20498 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/tdx/tdx.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/tdx/tdx.h
> @@ -8,6 +8,7 @@
>   #define TDG_VP_VMCALL_GET_TD_VM_CALL_INFO 0x10000
>   #define TDG_VP_VMCALL_REPORT_FATAL_ERROR 0x10003
>   
> +#define TDG_VP_VMCALL_INSTRUCTION_HLT 12
>   #define TDG_VP_VMCALL_INSTRUCTION_IO 30
>   #define TDG_VP_VMCALL_INSTRUCTION_RDMSR 31
>   #define TDG_VP_VMCALL_INSTRUCTION_WRMSR 32
> @@ -20,5 +21,6 @@ uint64_t tdg_vp_vmcall_get_td_vmcall_info(uint64_t *r11, uint64_t *r12,
>   					uint64_t *r13, uint64_t *r14);
>   uint64_t tdg_vp_vmcall_instruction_rdmsr(uint64_t index, uint64_t *ret_value);
>   uint64_t tdg_vp_vmcall_instruction_wrmsr(uint64_t index, uint64_t value);
> +uint64_t tdg_vp_vmcall_instruction_hlt(uint64_t interrupt_blocked_flag);
>   
>   #endif // SELFTEST_TDX_TDX_H
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/tdx/tdx.c b/tools/testing/selftests/kvm/lib/x86_64/tdx/tdx.c
> index 88ea6f2a6469..9485bafedc38 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/tdx/tdx.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/tdx/tdx.c
> @@ -114,3 +114,13 @@ uint64_t tdg_vp_vmcall_instruction_wrmsr(uint64_t index, uint64_t value)
>   
>   	return __tdx_hypercall(&args, 0);
>   }
> +
> +uint64_t tdg_vp_vmcall_instruction_hlt(uint64_t interrupt_blocked_flag)
> +{
> +	struct tdx_hypercall_args args = {
> +		.r11 = TDG_VP_VMCALL_INSTRUCTION_HLT,
> +		.r12 = interrupt_blocked_flag,
> +	};
> +
> +	return __tdx_hypercall(&args, 0);
> +}
> diff --git a/tools/testing/selftests/kvm/x86_64/tdx_vm_tests.c b/tools/testing/selftests/kvm/x86_64/tdx_vm_tests.c
> index 5db3701cc6d9..5fae4c6e5f95 100644
> --- a/tools/testing/selftests/kvm/x86_64/tdx_vm_tests.c
> +++ b/tools/testing/selftests/kvm/x86_64/tdx_vm_tests.c
> @@ -721,6 +721,83 @@ void verify_guest_msr_writes(void)
>   	printf("\t ... PASSED\n");
>   }
>   
> +/*
> + * Verifies HLT functionality.
> + */
> +void guest_hlt(void)
> +{
> +	uint64_t ret;
> +	uint64_t interrupt_blocked_flag;
> +
> +	interrupt_blocked_flag = 0;
> +	ret = tdg_vp_vmcall_instruction_hlt(interrupt_blocked_flag);
> +	if (ret)
> +		tdx_test_fatal(ret);
> +
> +	tdx_test_success();
> +}
> +
> +void _verify_guest_hlt(int signum);
> +
> +void wake_me(int interval)
> +{
> +	struct sigaction action;
> +
> +	action.sa_handler = _verify_guest_hlt;
> +	sigemptyset(&action.sa_mask);
> +	action.sa_flags = 0;
> +
> +	TEST_ASSERT(sigaction(SIGALRM, &action, NULL) == 0,
> +		    "Could not set the alarm handler!");
> +
> +	alarm(interval);
> +}
> +
> +void _verify_guest_hlt(int signum)
> +{
> +	struct kvm_vm *vm;
> +	static struct kvm_vcpu *vcpu;
> +
> +	/*
> +	 * This function will also be called by SIGALRM handler to check the
> +	 * vCPU MP State. If vm has been initialized, then we are in the signal
> +	 * handler. Check the MP state and let the guest run again.
> +	 */
> +	if (vcpu != NULL) {

What if the following case if there is a bug in KVM so that:

In guest, execution of tdg_vp_vmcall_instruction_hlt() return 0, but the
vcpu is not actually halted. Then guest will call tdx_test_success().

And the first call of _verify_guest_hlt() will call kvm_vm_free(vm) to free
the vm, which also frees the vcpu, and 1 second later, in this path vcpu 
will
be accessed after free.

> +		struct kvm_mp_state mp_state;
> +
> +		vcpu_mp_state_get(vcpu, &mp_state);
> +		TEST_ASSERT_EQ(mp_state.mp_state, KVM_MP_STATE_HALTED);
> +
> +		/* Let the guest to run and finish the test.*/
> +		mp_state.mp_state = KVM_MP_STATE_RUNNABLE;
> +		vcpu_mp_state_set(vcpu, &mp_state);
> +		return;
> +	}
> +
> +	vm = td_create();
> +	td_initialize(vm, VM_MEM_SRC_ANONYMOUS, 0);
> +	vcpu = td_vcpu_add(vm, 0, guest_hlt);
> +	td_finalize(vm);
> +
> +	printf("Verifying HLT:\n");
> +
> +	printf("\t ... Running guest\n");
> +
> +	/* Wait 1 second for guest to execute HLT */
> +	wake_me(1);
> +	td_vcpu_run(vcpu);
> +
> +	TDX_TEST_ASSERT_SUCCESS(vcpu);
> +
> +	kvm_vm_free(vm);
> +	printf("\t ... PASSED\n");
> +}
> +
> +void verify_guest_hlt(void)
> +{
> +	_verify_guest_hlt(0);
> +}
>   
>   int main(int argc, char **argv)
>   {
> @@ -740,6 +817,7 @@ int main(int argc, char **argv)
>   	run_in_new_process(&verify_guest_reads);
>   	run_in_new_process(&verify_guest_msr_writes);
>   	run_in_new_process(&verify_guest_msr_reads);
> +	run_in_new_process(&verify_guest_hlt);
>   
>   	return 0;
>   }