[patch 9/9] selftests/x86/iopl: Verify that CLI/STI result in #GP

Thomas Gleixner
2019-11-06T20:57:03Z

Add tests that the now emulated iopl() functionality does not longer
allow user space to disable interrupts.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
tools/testing/selftests/x86/iopl.c | 104 +++++++++++++++++++++++++++++++++----
1 file changed, 93 insertions(+), 11 deletions(-)

--- a/tools/testing/selftests/x86/iopl.c
+++ b/tools/testing/selftests/x86/iopl.c
@@ -35,6 +35,16 @@ static void sethandler(int sig, void (*h

}

+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 jmp_buf jmpbuf;

static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
@@ -42,22 +52,100 @@ static void sigsegv(int sig, siginfo_t *
siglongjmp(jmpbuf, 1);
}

+static bool try_outb(unsigned short port)
+{
+ sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
+ if (sigsetjmp(jmpbuf, 1) != 0) {
+ return false;
+ } else {
+ asm volatile ("outb %%al, %w[port]"
+ : : [port] "Nd" (port), "a" (0));
+ return true;
+ }
+ clearhandler(SIGSEGV);
+}
+
+static void expect_gp_outb(unsigned short port)
+{
+ if (try_outb(port)) {
+ printf("[FAIL]\toutb to 0x%02hx worked\n", port);
+ nerrs++;
+ }
+
+ printf("[OK]\toutb to 0x%02hx failed\n", port);
+}
+
+static bool try_cli(void)
+{
+ sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
+ if (sigsetjmp(jmpbuf, 1) != 0) {
+ return false;
+ } else {
+ asm volatile ("cli");
+ return true;
+ }
+ clearhandler(SIGSEGV);
+}
+
+static bool try_sti(void)
+{
+ sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
+ if (sigsetjmp(jmpbuf, 1) != 0) {
+ return false;
+ } else {
+ asm volatile ("sti");
+ return true;
+ }
+ clearhandler(SIGSEGV);
+}
+
+static void expect_gp_sti(void)
+{
+ if (try_sti()) {
+ printf("[FAIL]\tSTI worked\n");
+ nerrs++;
+ } else {
+ printf("[OK]\tSTI faulted\n");
+ }
+}
+
+static void expect_gp_cli(void)
+{
+ if (try_cli()) {
+ printf("[FAIL]\tCLI worked\n");
+ nerrs++;
+ } else {
+ printf("[OK]\tCLI faulted\n");
+ }
+}
+
int main(void)
{
cpu_set_t cpuset;
+
CPU_ZERO(&cpuset);
CPU_SET(0, &cpuset);
if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
err(1, "sched_setaffinity to CPU 0");

/* Probe for iopl support. Note that iopl(0) works even as nonroot. */
- if (iopl(3) != 0) {
+ switch(iopl(3)) {
+ case 0:
+ break;
+ case -ENOSYS:
+ printf("[OK]\tiopl() nor supported\n");
+ return 0;
+ default:
printf("[OK]\tiopl(3) failed (%d) -- try running as root\n",
errno);
return 0;
}

- /* Restore our original state prior to starting the test. */
+ /* Make sure that CLI/STI are blocked even with IOPL level 3 */
+ expect_gp_cli();
+ expect_gp_sti();
+
+ /* Restore our original state prior to starting the fork test. */
if (iopl(0) != 0)
err(1, "iopl(0)");

@@ -90,14 +178,9 @@ int main(void)

printf("[RUN]\tparent: write to 0x80 (should fail)\n");

- sethandler(SIGSEGV, sigsegv, 0);
- if (sigsetjmp(jmpbuf, 1) != 0) {
- printf("[OK]\twrite was denied\n");
- } else {
- asm volatile ("outb %%al, $0x80" : : "a" (0));
- printf("[FAIL]\twrite was allowed\n");
- nerrs++;
- }
+ expect_gp_outb(0x80);
+ expect_gp_cli();
+ expect_gp_sti();

/* Test the capability checks. */
printf("\tiopl(3)\n");
@@ -133,4 +216,3 @@ int main(void)
done:
return nerrs ? 1 : 0;
}
-