selftests/x86: Fix vDSO selftest segfault for vsyscall=none

The vDSO selftest tries to execute a vsyscall unconditionally, even if it
is not present on the test system (e.g. if booted with vsyscall=none or
with CONFIG_LEGACY_VSYSCALL_NONE=y set. Fix this by copying (and tweaking)
the vsyscall check from test_vsyscall.c

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kselftest@vger.kernel.org
Cc: shuah@kernel.org
Link: http://lkml.kernel.org/r/20180211111013.16888-3-linux@dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/testing/selftests/x86/test_vdso.c b/tools/testing/selftests/x86/test_vdso.c
index 29973cde06d3db08f5219dc692c82be82624e581..558c8207e7b9c09fd4b73503e60962dbd08bbea5 100644 (file)
--- a/tools/testing/selftests/x86/test_vdso.c
+++ b/tools/testing/selftests/x86/test_vdso.c
@@ -28,18 +28,52 @@
 
 int nerrs = 0;
 
+typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
+
+getcpu_t vgetcpu;
+getcpu_t vdso_getcpu;
+
+static void *vsyscall_getcpu(void)
+{
 #ifdef __x86_64__
-# define VSYS(x) (x)
+       FILE *maps;
+       char line[128];
+       bool found = false;
+
+       maps = fopen("/proc/self/maps", "r");
+       if (!maps) /* might still be present, but ignore it here, as we test vDSO not vsyscall */
+               return NULL;
+
+       while (fgets(line, sizeof(line), maps)) {
+               char r, x;
+               void *start, *end;
+               char name[128];
+               if (sscanf(line, "%p-%p %c-%cp %*x %*x:%*x %*u %s",
+                          &start, &end, &r, &x, name) != 5)
+                       continue;
+
+               if (strcmp(name, "[vsyscall]"))
+                       continue;
+
+               /* assume entries are OK, as we test vDSO here not vsyscall */
+               found = true;
+               break;
+       }
+
+       fclose(maps);
+
+       if (!found) {
+               printf("Warning: failed to find vsyscall getcpu\n");
+               return NULL;
+       }
+       return (void *) (0xffffffffff600800);
 #else
-# define VSYS(x) 0
+       return NULL;
 #endif
+}
 
-typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
-
-const getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
-getcpu_t vdso_getcpu;
 
-void fill_function_pointers()
+static void fill_function_pointers()
 {
        void *vdso = dlopen("linux-vdso.so.1",
                            RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
@@ -54,6 +88,8 @@ void fill_function_pointers()
        vdso_getcpu = (getcpu_t)dlsym(vdso, "__vdso_getcpu");
        if (!vdso_getcpu)
                printf("Warning: failed to find getcpu in vDSO\n");
+
+       vgetcpu = (getcpu_t) vsyscall_getcpu();
 }
 
 static long sys_getcpu(unsigned * cpu, unsigned * node,