kselftest/arm64: Run BTI selftests on systems without BTI

The BTI selftests are built both with and without BTI support, validating
both the generation of BTI signals as expected for binaries without BTI
support. Both versions of the binary currently skip all their tests when
the system does not support BTI, however this is excessive since we do have
a defined ABI for how the programs should function in this case (especially
for the non-BTI binary). Update the test program to run all the tests
unconditionally, adding a runtime adjustment of the expected results on
systems that don't support BTI where we currently handle the build time
case.

The tests all use HINT space instructions, BTI itself is a HINT as is
are the PAC instructions that function as landing pads, so nothing in the
tests depends on support for BTI in the kernel or hardware.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230110-arm64-bti-selftest-skip-v1-2-143ecdc84567@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/bti/test.c

@@ -6,6 +6,7 @@
 
 #include "system.h"
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <linux/errno.h>
 #include <linux/auxvec.h>
@@ -101,7 +102,8 @@ static void handler(int n, siginfo_t *si __always_unused,
 	uc->uc_mcontext.pstate &= ~PSR_BTYPE_MASK;
 }
 
-static int skip_all;
+/* Does the system have BTI? */
+static bool have_bti;
 
 static void __do_test(void (*trampoline)(void (*)(void)),
 		      void (*fn)(void),
@@ -109,19 +111,11 @@ static void __do_test(void (*trampoline)(void (*)(void)),
 		      const char *name,
 		      int expect_sigill)
 {
-	if (skip_all) {
-		test_skipped++;
-		putstr("ok ");
-		putnum(test_num++);
-		putstr(" ");
-		puttestname(name, trampoline_name);
-		putstr(" # SKIP\n");
-
-		return;
-	}
-
-	/* Branch Target exceptions should only happen in BTI binaries: */
-	if (!BTI)
+	/*
+	 * Branch Target exceptions should only happen for BTI
+	 * binaries running on a system with BTI:
+	 */
+	if (!BTI || !have_bti)
 		expect_sigill = 0;
 
 	sigill_expected = expect_sigill;
@@ -199,9 +193,10 @@ void start(int *argcp)
 		putstr("# HWCAP2_BTI present\n");
 		if (!(hwcap & HWCAP_PACA))
 			putstr("# Bad hardware?  Expect problems.\n");
+		have_bti = true;
 	} else {
 		putstr("# HWCAP2_BTI not present\n");
-		skip_all = 1;
+		have_bti = false;
 	}
 
 	putstr("# Test binary");