x86/selftests, x86/vm86: Improve entry_from_vm86 selftest

The entry_from_vm86 selftest was very weak.  Improve it: test
more types of kernel entries from vm86 mode and test them more
carefully.

While we're at it, try to improve behavior on non-SEP CPUs.  The
old code was buggy because I misunderstood the intended
semantics of #UD in vm86, so I didn't handle a possible signal.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/d8ef1d7368ac70d8342481563ed50f9a7d2eea6f.1436492057.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/testing/selftests/x86/entry_from_vm86.c

@@ -28,6 +28,55 @@
 static unsigned long load_addr = 0x10000;
 static int nerrs = 0;
 
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+		       int flags)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = handler;
+	sa.sa_flags = SA_SIGINFO | flags;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+static void clearhandler(int sig)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+static sig_atomic_t got_signal;
+
+static void sighandler(int sig, siginfo_t *info, void *ctx_void)
+{
+	ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+	if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM ||
+	    (ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) {
+		printf("[FAIL]\tSignal frame should not reflect vm86 mode\n");
+		nerrs++;
+	}
+
+	const char *signame;
+	if (sig == SIGSEGV)
+		signame = "SIGSEGV";
+	else if (sig == SIGILL)
+		signame = "SIGILL";
+	else
+		signame = "unexpected signal";
+
+	printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame,
+	       (unsigned long)ctx->uc_mcontext.gregs[REG_EFL],
+	       (unsigned short)ctx->uc_mcontext.gregs[REG_CS]);
+
+	got_signal = 1;
+}
+
 asm (
 	".pushsection .rodata\n\t"
 	".type vmcode_bound, @object\n\t"
@@ -38,6 +87,14 @@ asm (
 	"int3\n\t"
 	"vmcode_sysenter:\n\t"
 	"sysenter\n\t"
+	"vmcode_syscall:\n\t"
+	"syscall\n\t"
+	"vmcode_sti:\n\t"
+	"sti\n\t"
+	"vmcode_int3:\n\t"
+	"int3\n\t"
+	"vmcode_int80:\n\t"
+	"int $0x80\n\t"
 	".size vmcode, . - vmcode\n\t"
 	"end_vmcode:\n\t"
 	".code32\n\t"
@@ -45,9 +102,11 @@ asm (
 	);
 
 extern unsigned char vmcode[], end_vmcode[];
-extern unsigned char vmcode_bound[], vmcode_sysenter[];
+extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
+	vmcode_sti[], vmcode_int3[], vmcode_int80[];
 
 static void do_test(struct vm86plus_struct *v86, unsigned long eip,
+		    unsigned int rettype, unsigned int retarg,
 		    const char *text)
 {
 	long ret;
@@ -73,13 +132,28 @@ static void do_test(struct vm86plus_struct *v86, unsigned long eip,
 		else
 			sprintf(trapname, "%d", trapno);
 
-		printf("[OK]\tExited vm86 mode due to #%s\n", trapname);
+		printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
 	} else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
-		printf("[OK]\tExited vm86 mode due to unhandled GP fault\n");
+		printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
+	} else if (VM86_TYPE(ret) == VM86_TRAP) {
+		printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
+		       VM86_ARG(ret));
+	} else if (VM86_TYPE(ret) == VM86_SIGNAL) {
+		printf("[INFO]\tExited vm86 mode due to a signal\n");
+	} else if (VM86_TYPE(ret) == VM86_STI) {
+		printf("[INFO]\tExited vm86 mode due to STI\n");
 	} else {
-		printf("[OK]\tExited vm86 mode due to type %ld, arg %ld\n",
+		printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
 		       VM86_TYPE(ret), VM86_ARG(ret));
 	}
+
+	if (rettype == -1 ||
+	    (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
+		printf("[OK]\tReturned correctly\n");
+	} else {
+		printf("[FAIL]\tIncorrect return reason\n");
+		nerrs++;
+	}
 }
 
 int main(void)
@@ -105,10 +179,52 @@ int main(void)
 	assert((v86.regs.cs & 3) == 0);	/* Looks like RPL = 0 */
 
 	/* #BR -- should deliver SIG??? */
-	do_test(&v86, vmcode_bound - vmcode, "#BR");
-
-	/* SYSENTER -- should cause #GP or #UD depending on CPU */
-	do_test(&v86, vmcode_sysenter - vmcode, "SYSENTER");
+	do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
+
+	/*
+	 * SYSENTER -- should cause #GP or #UD depending on CPU.
+	 * Expected return type -1 means that we shouldn't validate
+	 * the vm86 return value.  This will avoid problems on non-SEP
+	 * CPUs.
+	 */
+	sethandler(SIGILL, sighandler, 0);
+	do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
+	clearhandler(SIGILL);
+
+	/*
+	 * SYSCALL would be a disaster in VM86 mode.  Fortunately,
+	 * there is no kernel that both enables SYSCALL and sets
+	 * EFER.SCE, so it's #UD on all systems.  But vm86 is
+	 * buggy (or has a "feature"), so the SIGILL will actually
+	 * be delivered.
+	 */
+	sethandler(SIGILL, sighandler, 0);
+	do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
+	clearhandler(SIGILL);
+
+	/* STI with VIP set */
+	v86.regs.eflags |= X86_EFLAGS_VIP;
+	v86.regs.eflags &= ~X86_EFLAGS_IF;
+	do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
+
+	/* INT3 -- should cause #BP */
+	do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
+
+	/* INT80 -- should exit with "INTx 0x80" */
+	v86.regs.eax = (unsigned int)-1;
+	do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
+
+	/* Execute a null pointer */
+	v86.regs.cs = 0;
+	v86.regs.ss = 0;
+	sethandler(SIGSEGV, sighandler, 0);
+	got_signal = 0;
+	do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer");
+	if (!got_signal) {
+		printf("[FAIL]\tDid not receive SIGSEGV\n");
+		nerrs++;
+	}
+	clearhandler(SIGSEGV);
 
 	return (nerrs == 0 ? 0 : 1);
 }