Re: [PATCH v3 7/7] selftests/mm: add more mseal traversal tests

[Pedro Falcato <pedro.falcato@gmail.com>]

On Wed, Aug 21, 2024 at 5:27 PM Jeff Xu <jeffxu@chromium.org> wrote:
>
> On Wed, Aug 21, 2024 at 9:20 AM Pedro Falcato <pedro.falcato@gmail.com> wrote:
> >
> > On Wed, Aug 21, 2024 at 4:56 PM Jeff Xu <jeffxu@chromium.org> wrote:
> > >
> > > Hi Pedro
> > >
> > > On Fri, Aug 16, 2024 at 5:18 PM Pedro Falcato <pedro.falcato@gmail.com> wrote:
> > > >
> > > > Add more mseal traversal tests across VMAs, where we could possibly
> > > > screw up sealing checks. These test more across-vma traversal for
> > > > mprotect, munmap and madvise. Particularly, we test for the case where a
> > > > regular VMA is followed by a sealed VMA.
> > > >
> > > > Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
> > > > ---
> > > >  tools/testing/selftests/mm/mseal_test.c | 111 +++++++++++++++++++++++++++++++-
> > > >  1 file changed, 110 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/tools/testing/selftests/mm/mseal_test.c b/tools/testing/selftests/mm/mseal_test.c
> > > > index 259bef4945e9..0d4d40fb0f88 100644
> > > > --- a/tools/testing/selftests/mm/mseal_test.c
> > > > +++ b/tools/testing/selftests/mm/mseal_test.c
> > > > @@ -766,6 +766,42 @@ static void test_seal_mprotect_partial_mprotect(bool seal)
> > > >         REPORT_TEST_PASS();
> > > >  }
> > > >
> > > > +static void test_seal_mprotect_partial_mprotect_tail(bool seal)
> > > > +{
> > > > +       void *ptr;
> > > > +       unsigned long page_size = getpagesize();
> > > > +       unsigned long size = 2 * page_size;
> > > > +       int ret;
> > > > +       int prot;
> > > > +
> > > > +       /*
> > > > +        * Check if a partial mseal (that results in two vmas) works correctly.
> > > > +        * It might mprotect the first, but it'll never touch the second (msealed) vma.
> > > > +        */
> > > > +
> > > > +       setup_single_address(size, &ptr);
> > > > +       FAIL_TEST_IF_FALSE(ptr != (void *)-1);
> > > > +
> > > > +       if (seal) {
> > > > +               ret = sys_mseal(ptr + page_size, size);
> > > you are allocating 2 pages , and I assume you are sealing the second
> > > page, so the size should be page_size.
> > > ret = sys_mseal(ptr + page_size, page_size);
> >
> > Yes, good catch, it appears to be harmless but ofc down to straight luck.
> > I'll send a fixup for this and the other mistake down there.
> >
> > >
> > > > +               FAIL_TEST_IF_FALSE(!ret);
> > > > +       }
> > > > +
> > > > +       ret = sys_mprotect(ptr, size, PROT_EXEC);
> > > > +       if (seal)
> > > > +               FAIL_TEST_IF_FALSE(ret < 0);
> > > > +       else
> > > > +               FAIL_TEST_IF_FALSE(!ret);
> > > > +
> > > > +       if (seal) {
> > > > +               FAIL_TEST_IF_FALSE(get_vma_size(ptr + page_size, &prot) > 0);
> > > > +               FAIL_TEST_IF_FALSE(prot == 0x4);
> > > To test partial mprotect, the test needs to add the check for the
> > > first page to be changed, Also to avoid the merge,  a PROT_NONE page
> > > can to be added in front.
> >
> > No, I'm leaving partial mprotect to be undefined. It doesn't make
> > sense to constraint ourselves, since POSIX wording is already loose.
> >
> > >
> > > > +       }
> > > > +
> > > > +       REPORT_TEST_PASS();
> > > > +}
> > > > +
> > > > +
> > > >  static void test_seal_mprotect_two_vma_with_gap(bool seal)
> > > >  {
> > > >         void *ptr;
> > > > @@ -983,6 +1019,41 @@ static void test_seal_munmap_vma_with_gap(bool seal)
> > > >         REPORT_TEST_PASS();
> > > >  }
> > > >
> > > > +static void test_seal_munmap_partial_across_vmas(bool seal)
> > > > +{
> > > > +       void *ptr;
> > > > +       unsigned long page_size = getpagesize();
> > > > +       unsigned long size = 2 * page_size;
> > > > +       int ret;
> > > > +       int prot;
> > > > +
> > > > +       /*
> > > > +        * Check if a partial mseal (that results in two vmas) works correctly.
> > > > +        * It might unmap the first, but it'll never unmap the second (msealed) vma.
> > > > +        */
> > > > +
> > > > +       setup_single_address(size, &ptr);
> > > > +       FAIL_TEST_IF_FALSE(ptr != (void *)-1);
> > > > +
> > > > +       if (seal) {
> > > > +               ret = sys_mseal(ptr + page_size, size);
> > > ret = sys_mseal(ptr + page_size, page_size);
> > >
> > > > +               FAIL_TEST_IF_FALSE(!ret);
> > > > +       }
> > > > +
> > > > +       ret = sys_munmap(ptr, size);
> > > > +       if (seal)
> > > > +               FAIL_TEST_IF_FALSE(ret < 0);
> > > > +       else
> > > > +               FAIL_TEST_IF_FALSE(!ret);
> > > > +
> > > > +       if (seal) {
> > > > +               FAIL_TEST_IF_FALSE(get_vma_size(ptr + page_size, &prot) > 0);
> > > > +               FAIL_TEST_IF_FALSE(prot == 0x4);
> > > To test partial unmap, the test needs to add the check for the first
> > > page to be freed, Also to avoid the merge,  a PROT_NONE page needs to
> > > be in front.
> >
> > I'm not testing partial unmap. Partial unmap does not happen. I have
> > told you this before.
> >
> ok.  Then this test should be as below ? (need to add PROT_NONE page
> before and after)
>   size = get_vma_size(ptr, &prot);
>   FAIL_TEST_IF_FALSE(size == 2 * page_size);
>   FAIL_TEST_IF_FALSE(prot==0x4)

That doesn't work because this region spans two vmas. I'll write
something similar for the fixup.

>
>
> > >
> > > The test_seal_munmap_partial_across_vmas  shows the behavior
> > > difference with in-loop approach and out-loop approach. Previously,
> > > both VMAs will not be freed, now the first VMA will be freed, and the
> > > second VMA (sealed) won't.
> > >
> > > This brings to the line you previously mentioned: [1] and I quote:
> > > "munmap is atomic and always has been. It's required by POSIX."
> >
> > This is still true, the comment was a copy-and-paste mindslip. Please
> > read the email thread. It has been fixed up by Andrew.
> >
> Which thread/patch by Andrew ? Could you please send it to me ? (I
> might missed that)

This thread and this patch:
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-add-more-mseal-traversal-tests-fix.patch

-- 
Pedro