Re: [PATCH v2] tools/testing/selftests: add merge test for partial msealed range

[Pedro Falcato]

On Tue, Mar 31, 2026 at 08:36:27AM +0100, Lorenzo Stoakes (Oracle) wrote:
> Commit 2697dd8ae721 ("mm/mseal: update VMA end correctly on merge") fixed
> an issue in the loop which iterates through VMAs applying mseal, which was
> triggered by mseal()'ing a range of VMAs where the second was mseal()'d and
> the first mergeable with it, once mseal()'d.
> 
> Add a regression test to assert that this behaviour is correct. We place it
> in the merge selftests as this is strictly an issue with merging (via a
> vma_modify() invocation).
> 
> It also assert that mseal()'d ranges are correctly merged as you'd expect.
> 
> The test is implemented such that it is skipped if mseal() is not
> available on the system.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
> ---
> v2:
> * Added tools/ based header so __NR_mseal should always be available.
> * However, for completeness, also check to see if defined, and assume ENOSYS if
>   not.
> * Thanks to Mike for reporting issues in his build on this test!
> 
> v1:
> https://lore.kernel.org/all/20260330135011.107036-1-ljs@xxxxxxxxxx/
> 
>  tools/testing/selftests/mm/merge.c | 89 ++++++++++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c
> index 10b686102b79..f73803b3679a 100644
> --- a/tools/testing/selftests/mm/merge.c
> +++ b/tools/testing/selftests/mm/merge.c
> @@ -2,6 +2,7 @@
> 
>  #define _GNU_SOURCE
>  #include "kselftest_harness.h"
> +#include <asm-generic/unistd.h>
>  #include <linux/prctl.h>
>  #include <fcntl.h>
>  #include <stdio.h>
> @@ -48,6 +49,19 @@ static pid_t do_fork(struct procmap_fd *procmap)
>  	return 0;
>  }
> 
> +#ifdef __NR_mseal
> +static int sys_mseal(void *ptr, size_t len, unsigned long flags)
> +{
> +	return syscall(__NR_mseal, (unsigned long)ptr, len, flags);
> +}
> +#else
> +static int sys_mseal(void *ptr, size_t len, unsigned long flags)
> +{
> +	errno = ENOSYS;
> +	return -1;
> +}
> +#endif
> +
>  FIXTURE_SETUP(merge)
>  {
>  	self->page_size = psize();
> @@ -1217,6 +1231,81 @@ TEST_F(merge, mremap_correct_placed_faulted)
>  	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size);
>  }
> 
> +TEST_F(merge, merge_vmas_with_mseal)
> +{
> +	unsigned int page_size = self->page_size;
> +	struct procmap_fd *procmap = &self->procmap;
> +	char *ptr, *ptr2, *ptr3;
> +	/* We need our own as cannot munmap() once sealed. */
> +	char *carveout;
> +
> +	/* Invalid mseal() call to see if implemented. */
> +	ASSERT_EQ(sys_mseal(NULL, 0, ~0UL), -1);
> +	if (errno == ENOSYS)
> +		SKIP(return, "mseal not supported, skipping.");
> +
> +	/* Map carveout. */
> +	carveout = mmap(NULL, 17 * page_size, PROT_NONE,
> +			MAP_PRIVATE | MAP_ANON, -1, 0);

I think it would be simpler if we did 5 pages (1 for each VMA, plus the two guard VMAs around it).

> +	ASSERT_NE(carveout, MAP_FAILED);
> +
> +	/*
> +	 * Map 3 separate VMAs:
> +	 *
> +	 * |-----------|-----------|-----------|
> +	 * |    RW     |    RWE    |    RO     |
> +	 * |-----------|-----------|-----------|
> +	 *      ptr         ptr2        ptr3
> +	 */

And now carveout += page_size; would leave us with

mmap(&carveout[0 * page_size])
mmap(&carveout[1 * page_size])
mmap(&carveout[2 * page_size])

and we don't need to deal with the arbitrary 5 pages below, which looks a good bit nicer.

> +	ptr = mmap(&carveout[page_size], 5 * page_size, PROT_READ | PROT_WRITE,
> +		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +	ASSERT_NE(ptr, MAP_FAILED);
> +	ptr2 = mmap(&carveout[page_size * 6], 5 * page_size,
> +		    PROT_READ | PROT_WRITE | PROT_EXEC,
> +		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +	ASSERT_NE(ptr2, MAP_FAILED);
> +	ptr3 = mmap(&carveout[page_size * 11], 5 * page_size, PROT_READ,
> +		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +	ASSERT_NE(ptr3, MAP_FAILED);
> +
> +	/*
> +	 * mseal the second VMA:
> +	 *
> +	 * |-----------|-----------|-----------|
> +	 * |    RW     |    RWES   |    RO     |
> +	 * |-----------|-----------|-----------|
> +	 *      ptr         ptr2        ptr3
> +	 */
> +	ASSERT_EQ(sys_mseal(ptr2, 5 * page_size, 0), 0);
> +
> +	/* Make first VMA mergeable upon mseal. */
> +	ASSERT_EQ(mprotect(ptr, 5 * page_size,
> +			   PROT_READ | PROT_WRITE | PROT_EXEC), 0);
> +	/*
> +	 * At this point we have:
> +	 *
> +	 * |-----------|-----------|-----------|
> +	 * |    RWE    |    RWES   |    RO     |
> +	 * |-----------|-----------|-----------|
> +	 *      ptr         ptr2        ptr3
> +	 *
> +	 * Now mseal all of the VMAs.
> +	 */
> +	ASSERT_EQ(sys_mseal(ptr, 15 * page_size, 0), 0);
> +
> +	/*
> +	 * We should end up with:
> +	 *
> +	 * |-----------------------|-----------|
> +	 * |          RWES         |    ROS    |
> +	 * |-----------------------|-----------|
> +	 *            ptr               ptr3
> +	 */
> +	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
> +	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
> +	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 10 * page_size);
> +}

Apart from these nits, the test LGTM

Acked-by: Pedro Falcato <pfalcato@xxxxxxx>

-- 
Pedro