[kvm-unit-tests PATCH v2 5/5] x86: VMX: Add tests for monitor trap flag

Oliver Upton
2020-01-28T09:27:41Z

Test to verify that MTF VM-exits into host are synthesized when the
'monitor trap flag' processor-based VM-execution control is set under
various conditions.

Expect an MTF VM-exit if instruction execution produces no events other
than MTF. Should instruction execution produce a concurrent debug-trap
and MTF event, expect an MTF VM-exit with the 'pending debug exceptions'
VMCS field set. Expect an MTF VM-exit to follow event delivery should
instruction execution generate a higher-priority event, such as a
general-protection fault. Lastly, expect an MTF VM-exit to follow
delivery of a debug-trap software exception (INT1/INT3/INTO/INT n).

Signed-off-by: Oliver Upton <oupton@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
---
x86/vmx.h | 1 +
x86/vmx_tests.c | 157 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 158 insertions(+)

diff --git a/x86/vmx.h b/x86/vmx.h
index 6214400f2b53..6adf0916564b 100644
--- a/x86/vmx.h
+++ b/x86/vmx.h
@@ -399,6 +399,7 @@ enum Ctrl0 {
CPU_NMI_WINDOW = 1ul << 22,
CPU_IO = 1ul << 24,
CPU_IO_BITMAP = 1ul << 25,
+ CPU_MTF = 1ul << 27,
CPU_MSR_BITMAP = 1ul << 28,
CPU_MONITOR = 1ul << 29,
CPU_PAUSE = 1ul << 30,
diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index b31c360c5f3c..0e2c2f8a7d34 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -4970,6 +4970,162 @@ static void test_vmx_preemption_timer(void)
vmcs_write(EXI_CONTROLS, saved_exit);
}

+extern unsigned char test_mtf1;
+extern unsigned char test_mtf2;
+extern unsigned char test_mtf3;
+
+__attribute__((noclone)) static void test_mtf_guest(void)
+{
+ asm ("vmcall;\n\t"
+ "out %al, $0x80;\n\t"
+ "test_mtf1:\n\t"
+ "vmcall;\n\t"
+ "out %al, $0x80;\n\t"
+ "test_mtf2:\n\t"
+ /*
+ * Prepare for the 'MOV CR3' test. Attempt to induce a
+ * general-protection fault by moving a non-canonical address into
+ * CR3. The 'MOV CR3' instruction does not take an imm64 operand,
+ * so we must MOV the desired value into a register first.
+ *
+ * MOV RAX is done before the VMCALL such that MTF is only enabled
+ * for the instruction under test.
+ */
+ "mov $0x8000000000000000, %rax;\n\t"
+ "vmcall;\n\t"
+ "mov %rax, %cr3;\n\t"
+ "test_mtf3:\n\t"
+ "vmcall;\n\t"
+ /*
+ * ICEBP/INT1 instruction. Though the instruction is now
+ * documented, don't rely on assemblers enumerating the
+ * instruction. Resort to hand assembly.
+ */
+ ".byte 0xf1;\n\t");
+}
+
+static void test_mtf_gp_handler(struct ex_regs *regs)
+{
+ regs->rip = (unsigned long) &test_mtf3;
+}
+
+static void test_mtf_db_handler(struct ex_regs *regs)
+{
+}
+
+static void enable_mtf(void)
+{
+ u32 ctrl0 = vmcs_read(CPU_EXEC_CTRL0);
+
+ vmcs_write(CPU_EXEC_CTRL0, ctrl0 | CPU_MTF);
+}
+
+static void disable_mtf(void)
+{
+ u32 ctrl0 = vmcs_read(CPU_EXEC_CTRL0);
+
+ vmcs_write(CPU_EXEC_CTRL0, ctrl0 & ~CPU_MTF);
+}
+
+static void enable_tf(void)
+{
+ unsigned long rflags = vmcs_read(GUEST_RFLAGS);
+
+ vmcs_write(GUEST_RFLAGS, rflags | X86_EFLAGS_TF);
+}
+
+static void disable_tf(void)
+{
+ unsigned long rflags = vmcs_read(GUEST_RFLAGS);
+
+ vmcs_write(GUEST_RFLAGS, rflags & ~X86_EFLAGS_TF);
+}
+
+static void report_mtf(const char *insn_name, unsigned long exp_rip)
+{
+ unsigned long rip = vmcs_read(GUEST_RIP);
+
+ assert_exit_reason(VMX_MTF);
+ report(rip == exp_rip, "MTF VM-exit after %s instruction. RIP: 0x%lx (expected 0x%lx)",
+ insn_name, rip, exp_rip);
+}
+
+static void vmx_mtf_test(void)
+{
+ unsigned long pending_dbg;
+ handler old_gp, old_db;
+
+ if (!(ctrl_cpu_rev[0].clr & CPU_MTF)) {
+ printf("CPU does not support the 'monitor trap flag' processor-based VM-execution control.\n");
+ return;
+ }
+
+ test_set_guest(test_mtf_guest);
+
+ /* Expect an MTF VM-exit after OUT instruction */
+ enter_guest();
+ skip_exit_vmcall();
+
+ enable_mtf();
+ enter_guest();
+ report_mtf("OUT", (unsigned long) &test_mtf1);
+ disable_mtf();
+
+ /*
+ * Concurrent #DB trap and MTF on instruction boundary. Expect MTF
+ * VM-exit with populated 'pending debug exceptions' VMCS field.
+ */
+ enter_guest();
+ skip_exit_vmcall();
+
+ enable_mtf();
+ enable_tf();
+
+ enter_guest();
+ report_mtf("OUT", (unsigned long) &test_mtf2);
+ pending_dbg = vmcs_read(GUEST_PENDING_DEBUG);
+ report(pending_dbg & DR_STEP,
+ "'pending debug exceptions' field after MTF VM-exit: 0x%lx (expected 0x%lx)",
+ pending_dbg, (unsigned long) DR_STEP);
+
+ disable_mtf();
+ disable_tf();
+ vmcs_write(GUEST_PENDING_DEBUG, 0);
+
+ /*
+ * #GP exception takes priority over MTF. Expect MTF VM-exit with RIP
+ * advanced to first instruction of #GP handler.
+ */
+ enter_guest();
+ skip_exit_vmcall();
+
+ old_gp = handle_exception(GP_VECTOR, test_mtf_gp_handler);
+
+ enable_mtf();
+ enter_guest();
+ report_mtf("MOV CR3", (unsigned long) get_idt_addr(&boot_idt[GP_VECTOR]));
+ disable_mtf();
+
+ /*
+ * Concurrent MTF and privileged software exception (i.e. ICEBP/INT1).
+ * MTF should follow the delivery of #DB trap, though the SDM doesn't
+ * provide clear indication of the relative priority.
+ */
+ enter_guest();
+ skip_exit_vmcall();
+
+ handle_exception(GP_VECTOR, old_gp);
+ old_db = handle_exception(DB_VECTOR, test_mtf_db_handler);
+
+ enable_mtf();
+ enter_guest();
+ report_mtf("INT1", (unsigned long) get_idt_addr(&boot_idt[DB_VECTOR]));
+ disable_mtf();
+
+ enter_guest();
+ handle_exception(DB_VECTOR, old_db);
+}
+
/*
* Tests for VM-execution control fields
*/
@@ -9505,5 +9661,6 @@ struct vmx_test vmx_tests[] = {
TEST(atomic_switch_max_msrs_test),
TEST(atomic_switch_overflow_msrs_test),
TEST(rdtsc_vmexit_diff_test),
+ TEST(vmx_mtf_test),
{ NULL, NULL, NULL, NULL, NULL, {0} },
};
--
2.25.0.341.g760bfbb309-goog