linux-hardening - Re: [PATCH v1] selftest mm/mseal: fix test_seal_mremap_move_dontunmap

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Message-ID: <CAKbZUD2xDdbxOTvR3-P=636jvhG_JPO3h79tgB59dfPmv046hg@mail.gmail.com>
Date: Wed, 7 Aug 2024 17:38:16 +0100
From: Pedro Falcato <pedro.falcato@...il.com>
To: jeffxu@...omium.org
Cc: akpm@...ux-foundation.org, willy@...radead.org, 
	torvalds@...ux-foundation.org, Liam.Howlett@...cle.com, jeffxu@...gle.com, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, dave.hansen@...el.com, linux-hardening@...r.kernel.org, 
	lorenzo.stoakes@...cle.com, mpe@...erman.id.au, oliver.sang@...el.com, 
	vbabka@...e.cz
Subject: Re: [PATCH v1] selftest mm/mseal: fix test_seal_mremap_move_dontunmap_anyaddr

On Wed, Aug 7, 2024 at 4:35 PM <jeffxu@...omium.org> wrote:
<snip>
>         /* shrink from 4 pages to 2 pages. */
> -       ret2 = mremap(ptr, size, 2 * page_size, 0, 0);
> +       ret2 = sys_mremap(ptr, size, 2 * page_size, 0, 0);
>         if (seal) {
> -               FAIL_TEST_IF_FALSE(ret2 == MAP_FAILED);
> +               FAIL_TEST_IF_FALSE(ret2 == (void *) MAP_FAILED);

MAP_FAILED is already void *

<snip>
> @@ -1449,18 +1457,16 @@ static void test_seal_mremap_move_dontunmap_anyaddr(bool seal)
>         }
>
>         /*
> -        * The 0xdeaddead should not have effect on dest addr
> +        * The 0xdead0000 should not have effect on dest addr
>          * when MREMAP_DONTUNMAP is set.
>          */
> -       ret2 = mremap(ptr, size, size, MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
> -                       0xdeaddead);
> +       ret2 = sys_mremap(ptr, size, size, MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
> +                       (void *) 0xdead0000);

You still didn't explain why this test is actually needed. Why are you
testing MREMAP_DONTUNMAP's hint system?
This has nothing to do with mseal, you already test the
MREMAP_DONTUNMAP and MREMAP_FIXED paths in other tests.
You also don't know if 0xdead0000 is a valid page (hexagon for
instance seems to support 256KiB and 1MiB pages, so does ppc32, and
this is not something that should be hardcoded).

I'm not a fan of just throwing random flags for tests, it should be
somewhat logical.

-- 
Pedro