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

Andy Lutomirski
2019-03-01T19:59:40Z

> On Feb 28, 2019, at 4:18 PM, Steve Muckle <smuckle@google.com> wrote:
>
> 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.

NAK. If you want an old buggy kernel to pass a test, please either
patch the kernel or run an old test.

>
> Signed-off-by: Steve Muckle <smuckle@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
>