[PATCH] selftests: x86: add version check in test_syscall_vdso

[Steve Muckle]

Since 4.17 registers r8-r11 are not clobbered/zeroed by a 64-bit kernel
handling a 32-bit syscall and this behavior is enforced by the
test_syscall_vdso testcase. See commit 8bb2610bc496
("x86/entry/64/compat: Preserve r8-r11 in int $0x80").

Permit the old behavior in the testcase for kernels prior to 4.17.

Signed-off-by: Steve Muckle <smuc...@google.com>
---
 .../testing/selftests/x86/test_syscall_vdso.c | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/tools/testing/selftests/x86/test_syscall_vdso.c 
b/tools/testing/selftests/x86/test_syscall_vdso.c
index c9c3281077bc..f7284dc4c32b 100644
--- a/tools/testing/selftests/x86/test_syscall_vdso.c
+++ b/tools/testing/selftests/x86/test_syscall_vdso.c
@@ -30,6 +30,7 @@
 #include <sys/time.h>
 #include <elf.h>
 #include <sys/ptrace.h>
+#include <sys/utsname.h>
 #include <sys/wait.h>
 
 #if !defined(__i386__)
@@ -71,6 +72,7 @@ struct regs64 {
 };
 struct regs64 regs64;
 int kernel_is_64bit;
+int clobber_ok;
 
 asm (
        "       .pushsection .text\n"
@@ -130,6 +132,28 @@ void print_regs64(void)
        printf("12:%016llx 13:%016llx 14:%016llx 15:%016llx\n", regs64.r12,  
regs64.r13,  regs64.r14,  regs64.r15);
 }
 
+static void get_kernel_version(int *version, int *patchlevel)
+{
+       int ret, sublevel;
+       struct utsname utsname;
+
+       ret = uname(&utsname);
+       if (ret) {
+               perror("uname");
+               exit(1);
+       }
+
+       ret = sscanf(utsname.release, "%d.%d.%d", version, patchlevel,
+                    &sublevel);
+       if (ret < 0) {
+               perror("sscanf");
+               exit(1);
+       } else if (ret != 3) {
+               printf("Malformed kernel version %s\n", &utsname.release);
+               exit(1);
+       }
+}
+
 int check_regs64(void)
 {
        int err = 0;
@@ -166,6 +190,8 @@ int check_regs64(void)
                         * Historically (and probably unintentionally), they
                         * were clobbered or zeroed.
                         */
+                       if (clobber_ok && *r64 == 0 && num <= 11)
+                               continue;
                }
                printf("[FAIL]\tR%d has changed:%016llx\n", num, *r64);
                err++;
@@ -385,6 +411,7 @@ int main(int argc, char **argv, char **envp)
 {
        int exitcode = 0;
        int cs;
+       int version, patchlevel;
 
        asm("\n"
        "       movl    %%cs, %%eax\n"
@@ -394,6 +421,9 @@ int main(int argc, char **argv, char **envp)
        if (!kernel_is_64bit)
                printf("[NOTE]\tNot a 64-bit kernel, won't test R8..R15 
leaks\n");
 
+       get_kernel_version(&version, &patchlevel);
+       clobber_ok = version < 4 || (version == 4 && patchlevel < 17);
+
        /* This only works for non-static builds:
         * syscall_addr = dlsym(dlopen("linux-gate.so.1", RTLD_NOW), 
"__kernel_vsyscall");
         */
-- 
2.21.0.352.gf09ad66450-goog