[tip:x86/pti] selftests/x86: Fix vDSO selftest segfault for vsyscall=none

[tip-bot for Dominik Brodowski]

Commit-ID:  198ee8e17502da2634f7366395db1d77630e0219
Gitweb:     https://git.kernel.org/tip/198ee8e17502da2634f7366395db1d77630e0219
Author:     Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
AuthorDate: Sun, 11 Feb 2018 12:10:10 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 13 Feb 2018 09:04:55 +0100

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@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kselftest@xxxxxxxxxxxxxxx
Cc: shuah@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20180211111013.16888-3-linux@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 tools/testing/selftests/x86/test_vdso.c | 50 ++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/x86/test_vdso.c b/tools/testing/selftests/x86/test_vdso.c
index 29973cd..558c820 100644
--- 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,