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Date:   Sun, 17 Feb 2019 08:50:15 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Mike Travis <travis@....com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v3 3/6] mm: Add build time sanity check for struct page size

On Sat, Feb 16, 2019 at 6:02 AM Baoquan He <bhe@...hat.com> wrote:
>
> Size of struct page might be larger than 64 bytes if debug options
> enabled, or fields added for debugging intentionally. Yet an upper
> limit need be added at build time to trigger an alert in case the
> size is too big to boot up system, warning people to check if it's
> be done on purpose in advance.
>
> Here 1/4 of PAGE_SIZE is chosen since system must have been insane
> with this value. For those systems with PAGE_SIZE larger than 4KB,
> 1KB is simply taken.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/page_alloc.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 35fdde041f5c..eb6c8e22333b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -67,6 +67,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/nmi.h>
>  #include <linux/psi.h>
> +#include <linux/sizes.h>
>
>  #include <asm/sections.h>
>  #include <asm/tlbflush.h>
> @@ -7084,6 +7085,7 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn)
>         unsigned long start_pfn, end_pfn;
>         int i, nid;
>
> +       BUILD_BUG_ON(sizeof(struct page) > min_t(size_t, SZ_1K, PAGE_SIZE));

Are there systems with PAGE_SIZE < 1K? Maybe this should just be a
direct SZ_1K check?
(Also, perhaps this should use the new static_assert where struct page
is defined?)

-Kees

>         /* Record where the zone boundaries are */
>         memset(arch_zone_lowest_possible_pfn, 0,
>                                 sizeof(arch_zone_lowest_possible_pfn));
> --
> 2.17.2
>


-- 
Kees Cook

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