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Message-ID: <9d4c0d27-0ebd-4c6d-af38-d32ef420fde4@redhat.com>
Date: Wed, 27 Aug 2025 13:58:50 -0400
From: Waiman Long <llong@...hat.com>
To: André Almeida <andrealmeid@...lia.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
linux-kernel@...r.kernel.org
Cc: Darren Hart <dvhart@...radead.org>, Davidlohr Bueso <dave@...olabs.net>,
Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>,
Valentin Schneider <vschneid@...hat.com>, Borislav Petkov <bp@...en8.de>,
kernel-dev@...lia.com
Subject: Re: [PATCH] selftests/futex: Fix futex_numa_mpol's memory out of
range subtest
On 8/27/25 11:44 AM, André Almeida wrote:
> The "Memory out of range" subtest works by pointing the futex pointer
> to the memory exactly after the allocated map (futex_ptr + mem_size).
> This address is out of the allocated range for futex_ptr, but depending
> on the memory layout, it might be pointing to a valid memory address of
> the process. In order to make this test deterministic, create a "buffer
> zone" with PROT_NONE just before allocating the valid futex_ptr memory,
> to make sure that futex_ptr + mem_size falls into a memory address that
> will return an invalid access error.
>
> Fixes: 3163369407ba ("selftests/futex: Add futex_numa_mpol")
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> This patch comes from this series:
> https://lore.kernel.org/lkml/20250704-tonyk-robust_test_cleanup-v1-13-c0ff4f24c4e1@igalia.com/
> ---
> .../futex/functional/futex_numa_mpol.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/futex/functional/futex_numa_mpol.c b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> index a9ecfb2d3932..1eb3e67d999b 100644
> --- a/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> +++ b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> @@ -143,7 +143,7 @@ int main(int argc, char *argv[])
> {
> struct futex32_numa *futex_numa;
> int mem_size, i;
> - void *futex_ptr;
> + void *futex_ptr, *buffer_zone;
> int c;
>
> while ((c = getopt(argc, argv, "chv:")) != -1) {
> @@ -168,6 +168,17 @@ int main(int argc, char *argv[])
> ksft_set_plan(1);
>
> mem_size = sysconf(_SC_PAGE_SIZE);
> +
> + /*
> + * The "Memory out of range" test depends on having a pointer to an
> + * invalid address. To make this test deterministic, and to not depend
> + * on the memory layout of the process, create a "buffer zone" with
> + * PROT_NONE just before the valid memory (*futex_ptr).
> + */
> + buffer_zone = mmap(NULL, mem_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> + if (buffer_zone == MAP_FAILED)
> + ksft_exit_fail_msg("mmap() for %d bytes failed\n", mem_size);
> +
> futex_ptr = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> if (futex_ptr == MAP_FAILED)
> ksft_exit_fail_msg("mmap() for %d bytes failed\n", mem_size);
This patch makes the assumption that consecutive mmap() calls will
allocate pages consecutively downward from a certain address. I don't
know if this assumption will be valid in all cases. I think it will be
safer to just allocate the 2-page memory block and then change the 2nd
page protection to PROT_NONE to make it a guard page.
Cheers,
Longman
> @@ -229,6 +240,10 @@ int main(int argc, char *argv[])
> }
> }
> }
> +
> + munmap(buffer_zone, mem_size);
> + munmap(futex_ptr, mem_size);
> +
> ksft_test_result_pass("NUMA MPOL tests passed\n");
> ksft_finished();
> return 0;
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