Re: [RFC PATCH v5 2/7] selftests: x86: test_mremap_vdso: skip if vdso is msealed

[Jeff Xu <jeffxu@chromium.org>]

On Wed, Feb 12, 2025 at 5:04 AM Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> On Wed, Feb 12, 2025 at 03:21:50AM +0000, jeffxu@chromium.org wrote:
> > From: Jeff Xu <jeffxu@chromium.org>
> >
> > Add code to detect if the vdso is memory sealed, skip the test
> > if it is.
> >
> > Signed-off-by: Jeff Xu <jeffxu@chromium.org>
> > ---
> >  .../testing/selftests/x86/test_mremap_vdso.c  | 38 +++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >
> > diff --git a/tools/testing/selftests/x86/test_mremap_vdso.c b/tools/testing/selftests/x86/test_mremap_vdso.c
> > index d53959e03593..c68077c56b22 100644
> > --- a/tools/testing/selftests/x86/test_mremap_vdso.c
> > +++ b/tools/testing/selftests/x86/test_mremap_vdso.c
> > @@ -14,6 +14,7 @@
> >  #include <errno.h>
> >  #include <unistd.h>
> >  #include <string.h>
> > +#include <stdbool.h>
> >
> >  #include <sys/mman.h>
> >  #include <sys/auxv.h>
> > @@ -55,13 +56,50 @@ static int try_to_remap(void *vdso_addr, unsigned long size)
> >
> >  }
> >
> > +#define VDSO_NAME "[vdso]"
> > +#define VMFLAGS "VmFlags:"
> > +#define MSEAL_FLAGS "sl"
> > +#define MAX_LINE_LEN 512
> > +
> > +bool vdso_sealed(FILE *maps)
> > +{
> > +     char line[MAX_LINE_LEN];
> > +     bool has_vdso = false;
> > +
> > +     while (fgets(line, sizeof(line), maps)) {
> > +             if (strstr(line, VDSO_NAME))
> > +                     has_vdso = true;
> > +
> > +             if (has_vdso && !strncmp(line, VMFLAGS, strlen(VMFLAGS))) {
> > +                     if (strstr(line, MSEAL_FLAGS))
> > +                             return true;
> > +
> > +                     return false;
>
> This only tests that any mapping after the vdso is sealed.

The code above begins by searching for the "[vdso]" string, then looks
for the first line that starts with "VmFlags:", and looks for the "sl"
substring within that line. We're assuming the format of smaps won't
change from release to release.

> There is a real parser for /proc/self/smaps in
> tools/testing/selftests/mm/vm_util.[ch], see check_vmflag_io().
>
This test is in selftest/x86, which makes it hard to include the
vm_util from selftest/mm, if that's what you're asking.

If you are asking reusing the code logic from vm_util, the
check_vmflag_io() calls __get_smap_entry(addr, "VmFlags:", ...), which
begins by searching for address, then looks for the first line that
started with "VmFlags:", then check for the "io" within that line.
This is the same logic as my code, if I read the code correctly.

Thanks
-Jeff



> > +             }
> > +     }
> > +
> > +     return false;
> > +}
>
> <snip>