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

[Kees Cook <kees@kernel.org>]

On February 13, 2025 6:14:00 AM PST, Jeff Xu <jeffxu@chromium.org> wrote:
>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.

Oh, I missed this in my reviews: nothing _resets_ has_vdso to false, so if any other mapping follows vdso that happens to be sealed, this will return true...

>
>> 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.

Hm, we have done these kinds of inter-tests dependencies before. (E.g. seccomp includes stuff from the clone tests.) I think it should be possible if it can just be a header include. Linking across tests would be more frustrating.

-Kees

-- 
Kees Cook