selftests/seccomp: fix syscall_restart test for arm compat

[ Upstream commit 797002deed03491215a352ace891749b39741b69 ]

The inconsistencies in the systcall ABI between arm and arm-compat can
can cause a failure in the syscall_restart test due to the logic
attempting to work around the differences. The 'machine' field for an
ARM64 device running in compat mode can report 'armv8l' or 'armv8b'
which matches with the string 'arm' when only examining the first three
characters of the string.

This change adds additional validation to the workaround logic to make
sure we only take the arm path when running natively, not in arm-compat.

Fixes: 256d0afb11d6 ("selftests/seccomp: build and pass on arm64")
Signed-off-by: Neill Kapron <nkapron@google.com>
Link: https://lore.kernel.org/r/20250427094103.3488304-2-nkapron@google.com
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 413a7b9f3c4d3f8848f9fbd72b99d7162d3aef08..7f62635226fd3c368023d12f7ee65938edf7a41f 100644 (file)
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -3081,12 +3081,15 @@ TEST(syscall_restart)
        ret = get_syscall(_metadata, child_pid);
 #if defined(__arm__)
        /*
-        * FIXME:
         * - native ARM registers do NOT expose true syscall.
         * - compat ARM registers on ARM64 DO expose true syscall.
+        * - values of utsbuf.machine include 'armv8l' or 'armb8b'
+        *   for ARM64 running in compat mode.
         */
        ASSERT_EQ(0, uname(&utsbuf));
-       if (strncmp(utsbuf.machine, "arm", 3) == 0) {
+       if ((strncmp(utsbuf.machine, "arm", 3) == 0) &&
+           (strncmp(utsbuf.machine, "armv8l", 6) != 0) &&
+           (strncmp(utsbuf.machine, "armv8b", 6) != 0)) {
                EXPECT_EQ(__NR_nanosleep, ret);
        } else
 #endif