Re: [LTP] [PATCH v1] security/dirtyc0w_shmem: Fix remaining cases where UFFD_FEATURE_MINOR_SHMEM is absent

[Petr Vorel <pvorel@suse.cz>]

Hi David,

> When UFFD_FEATURE_MINOR_SHMEM is not defined, we still have to make the
> checkpoint happy, otherwise our parent process will run into a timeout.
> Further, we have to test if UFFD_FEATURE_MINOR_SHMEM is really returned by
> the UFFD_API ioctl: if the kernel knows about the feature but doesn't
> support it, it will be masked off.

> Reported-by: Martin Doucha <mdoucha@suse.cz>
> Cc: Petr Vorel <pvorel@suse.cz>
> Cc: Cyril Hrubis <chrubis@suse.cz>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  .../dirtyc0w_shmem/dirtyc0w_shmem_child.c        | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)

> diff --git a/testcases/kernel/security/dirtyc0w_shmem/dirtyc0w_shmem_child.c b/testcases/kernel/security/dirtyc0w_shmem/dirtyc0w_shmem_child.c
> index cb2e9df0c..c117c6f39 100644
> --- a/testcases/kernel/security/dirtyc0w_shmem/dirtyc0w_shmem_child.c
> +++ b/testcases/kernel/security/dirtyc0w_shmem/dirtyc0w_shmem_child.c
> @@ -24,12 +24,12 @@
>  #include <linux/userfaultfd.h>
>  #endif

> -#ifdef UFFD_FEATURE_MINOR_SHMEM
Shouldn't be the check and TST_TEST_TCONF() actually be in dirtyc0w_shmem.c?
I overlooked that, but IMHO test does not make sense at all if
UFFD_FEATURE_MINOR_SHMEM not defined, right?

Also Martin noted that ("The parent process should not even fork() when
UFFD_FEATURE_MINOR_SHMEM is not defined in config.h.").

Therefore one fix would be to move the check to parent and second
(maybe better in separate commit) to add check for uffdio_api.features.

Kind regards,
Petr

> -
>  #define TST_NO_DEFAULT_MAIN
>  #include "tst_test.h"
>  #include "tst_safe_macros.h"
>  #include "tst_safe_pthread.h"
> +
> +#ifdef UFFD_FEATURE_MINOR_SHMEM
>  #include "lapi/syscalls.h"

>  #define TMP_DIR "tmp_dirtyc0w_shmem"
> @@ -162,6 +162,10 @@ retry:
>  			"Could not create userfault file descriptor");
>  	}

> +	if (!(uffdio_api.features & UFFD_FEATURE_MINOR_SHMEM))
> +		tst_brk(TCONF,
> +			"System does not have userfaultfd minor fault support for shmem");
> +
>  	uffdio_register.range.start = (unsigned long) map;
>  	uffdio_register.range.len = page_size;
>  	uffdio_register.mode = UFFDIO_REGISTER_MODE_MINOR;
> @@ -236,6 +240,10 @@ int main(void)
>  	return 0;
>  }
>  #else /* UFFD_FEATURE_MINOR_SHMEM */
> -#include "tst_test.h"
> -TST_TEST_TCONF("System does not have userfaultfd minor fault support for shmem");
> +int main(void)
> +{
> +	tst_reinit();
> +	TST_CHECKPOINT_WAKE(0);
> +	tst_brk(TCONF, "System does not have userfaultfd minor fault support for shmem");
> +}
>  #endif /* UFFD_FEATURE_MINOR_SHMEM */

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