Re: [PATCH] munmap sealed memory cause memory to split (bug)

[Jeff Xu <jeffxu@chromium.org>]

On Thu, Oct 17, 2024 at 1:18 AM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> NACK. Greg's bot got to it but...
>
> As per Greg's bot, no signed-off-by line.
>
Sorry for confusion, I wasn't meant to send this as a PATCH, but
reporting the issue.
The diff was just sent as reference to repro the bug, and I forgot to
remove PATCH from the title. I apologize for the confusion.

-Jeff


> The subject should be something about adding a test.
>
> You later say you are somehow dependning on things (what?) to make this work but
> it's broken.
>
> Jeff - you're doing things that were raised on previous reviews as if we
> never said them. It's starting to get annoying now. Please try to listen to
> upstream.
>
> On Thu, Oct 17, 2024 at 02:26:27AM +0000, jeffxu@chromium.org wrote:
> > From: Jeff Xu <jeffxu@google.com>
> >
> > It appears there is a regression on the latest mm,
> > when munmap sealed memory, it can cause unexpected VMA split.
> > E.g. repro use this test.
>
> This is an unacceptably short commit message. You've been told about this
> before.
>
> > ---
> >  tools/testing/selftests/mm/mseal_test.c | 76 +++++++++++++++++++++++++
> >  1 file changed, 76 insertions(+)
> >
> > diff --git a/tools/testing/selftests/mm/mseal_test.c b/tools/testing/selftests/mm/mseal_test.c
> > index fa74dbe4a684..0af33e13b606 100644
> > --- a/tools/testing/selftests/mm/mseal_test.c
> > +++ b/tools/testing/selftests/mm/mseal_test.c
> > @@ -1969,6 +1969,79 @@ static void test_madvise_filebacked_was_writable(bool seal)
> >       REPORT_TEST_PASS();
> >  }
> >
> > +static void test_munmap_free_multiple_ranges_with_split(bool seal)
> > +{
> > +     void *ptr;
> > +     unsigned long page_size = getpagesize();
> > +     unsigned long size = 12 * page_size;
> > +     int ret;
> > +     int prot;
> > +
> > +     setup_single_address(size, &ptr);
> > +     FAIL_TEST_IF_FALSE(ptr != (void *)-1);
>
> I'm not going to accept any test where you do:
>
>         FAIL_TEST_IF_FALSE(<negation>)
>
> As that's totally unreadable. I asked you before for justification and you
> didn't provide it, no other tests appear to do this, I wrote thousands of
> lines of tests recently without doing this - stop it.
>
> Also referene MAP_FAILED here please. You've been told before.
>
> > +
> > +     /* seal the middle 4 page */
> > +     if (seal) {
> > +             ret = sys_mseal(ptr + 4 * page_size, 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(!ret);
> > +
> > +             size = get_vma_size(ptr, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
>
> Again, you've been told before, stop referencing numbers instead of
> PROT_... flags.
>
> OK I'm stopping at this point, you _must listen to review_ Jeff.
>
> > +
> > +             size = get_vma_size(ptr +  4 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +
> > +             size = get_vma_size(ptr +  8 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +     }
> > +
> > +     /* munmap 4  pages from the third page */
> > +     ret = sys_munmap(ptr + 2 * page_size, 4 * page_size);
> > +     if (seal) {
> > +             FAIL_TEST_IF_FALSE(ret);
> > +             FAIL_TEST_IF_FALSE(errno == EPERM);
> > +
> > +             size = get_vma_size(ptr, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +
> > +             size = get_vma_size(ptr +  4 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +
> > +             size = get_vma_size(ptr +  8 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +     } else
> > +             FAIL_TEST_IF_FALSE(!ret);
> > +
> > +     /* munmap 4 pages from the sealed page */
> > +     ret = sys_munmap(ptr + 6 * page_size, 4 * page_size);
> > +     if (seal) {
> > +             FAIL_TEST_IF_FALSE(ret);
> > +             FAIL_TEST_IF_FALSE(errno == EPERM);
> > +
> > +             size = get_vma_size(ptr + 4 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +
> > +             size = get_vma_size(ptr +  4 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +
> > +             size = get_vma_size(ptr +  8 * page_size, &prot);
> > +             FAIL_TEST_IF_FALSE(size == 4 * page_size);
> > +             FAIL_TEST_IF_FALSE(prot == 4);
> > +     } else
> > +             FAIL_TEST_IF_FALSE(!ret);
> > +
> > +     REPORT_TEST_PASS();
> > +}
> > +
> > +
> >  int main(int argc, char **argv)
> >  {
> >       bool test_seal = seal_support();
> > @@ -2099,5 +2172,8 @@ int main(int argc, char **argv)
> >       test_madvise_filebacked_was_writable(false);
> >       test_madvise_filebacked_was_writable(true);
> >
> > +     test_munmap_free_multiple_ranges_with_split(false);
> > +     test_munmap_free_multiple_ranges_with_split(true);
> > +
> >       ksft_finished();
> >  }
> > --
> > 2.47.0.rc1.288.g06298d1525-goog
> >