[PATCH 4.14 067/167] selftests/x86: Fix vDSO selftest segfault for vsyscall=none

Greg Kroah-Hartman
2018-02-21T12:47:58Z

From: Dominik Brodowski <linux@dominikbrodowski.net>

commit 198ee8e17502da2634f7366395db1d77630e0219 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/testing/selftests/x86/test_vdso.c | 50 +++++++++++++++++++++++++++-----
1 file changed, 43 insertions(+), 7 deletions(-)

--- 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,