linux-kernel - Re: [PATCH v2 2/5] kselftest: vm: Fix mdwe's mmap

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Date:   Mon, 22 May 2023 10:53:20 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Florent Revest <revest@...omium.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, catalin.marinas@....com,
        anshuman.khandual@....com, joey.gouly@....com, mhocko@...e.com,
        keescook@...omium.org, peterx@...hat.com, izbyshev@...ras.ru,
        broonie@...nel.org, szabolcs.nagy@....com, kpsingh@...nel.org,
        gthelen@...gle.com, toiwoton@...il.com
Subject: Re: [PATCH v2 2/5] kselftest: vm: Fix mdwe's mmap_FIXED test case

On 17.05.23 17:03, Florent Revest wrote:
> I checked with the original author, the mmap_FIXED test case wasn't
> properly tested and fails. Currently, it maps two consecutive (non
> overlapping) pages and expects the second mapping to be denied by MDWE
> but these two pages have nothing to do with each other so MDWE is
> actually out of the picture here.
> 
> What the test actually intended to do was to remap a virtual address
> using MAP_FIXED. However, this operation unmaps the existing mapping and
> creates a new one so the va is backed by a new page and MDWE is again
> out of the picture, all remappings should succeed.
> 
> This patch keeps the test case to make it clear that this situation is
> expected to work.
> 
> Signed-off-by: Florent Revest <revest@...omium.org>
> Fixes: 4cf1fe34fd18 ("kselftest: vm: add tests for memory-deny-write-execute")
> ---
>   tools/testing/selftests/mm/mdwe_test.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
> index d0954c657feb..91aa9c3099e7 100644
> --- a/tools/testing/selftests/mm/mdwe_test.c
> +++ b/tools/testing/selftests/mm/mdwe_test.c
> @@ -168,13 +168,10 @@ TEST_F(mdwe, mmap_FIXED)
>   	self->p = mmap(NULL, self->size, PROT_READ, self->flags, 0, 0);
>   	ASSERT_NE(self->p, MAP_FAILED);
>   
> -	p = mmap(self->p + self->size, self->size, PROT_READ | PROT_EXEC,
> +	/* MAP_FIXED unmaps the existing page before mapping which is allowed */
> +	p = mmap(self->p, self->size, PROT_READ | PROT_EXEC,
>   		 self->flags | MAP_FIXED, 0, 0);
> -	if (variant->enabled) {
> -		EXPECT_EQ(p, MAP_FAILED);
> -	} else {
> -		EXPECT_EQ(p, self->p);
> -	}
> +	EXPECT_EQ(p, self->p);
>   }
>   
>   TEST_F(mdwe, arm64_BTI)

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb