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Subject: Re: [PATCH mm] mm, kasan: fix for "integrate page_alloc init with
 HW_TAGS"
To:     Andrey Konovalov <andreyknvl@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Sergei Trofimovich <slyfox@gentoo.org>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <2e5e80481533e73876d5d187d1f278f9656df73a.1617118134.git.andreyknvl@google.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <115c3cd4-a5ec-ea4c-fdc8-a17a0990bd30@suse.cz>
Date:   Tue, 30 Mar 2021 17:54:33 +0200
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On 3/30/21 5:31 PM, Andrey Konovalov wrote:
> My commit "integrate page_alloc init with HW_TAGS" changed the order of
> kernel_unpoison_pages() and kernel_init_free_pages() calls. This leads
> to __GFP_ZERO allocations being incorrectly poisoned when page poisoning
> is enabled.

Correction: This leads to check_poison_mem() complain about memory corruption
because the poison pattern has already been overwritten by zeroes.

> Fix by restoring the initial order. Also add a warning comment.
> 
> Reported-by: Vlastimil Babka <vbabka@suse.cz>
> Reported-by: Sergei Trofimovich <slyfox@gentoo.org>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

I expect this will be folded to your patch in mmotm anyway, so the changelog is
not as important...

> ---
>  mm/page_alloc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 033bd92e8398..1fc5061f8ca1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2328,6 +2328,12 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>  	arch_alloc_page(page, order);
>  	debug_pagealloc_map_pages(page, 1 << order);
>  
> +	/*
> +	 * Page unpoisoning must happen before memory initialization.
> +	 * Otherwise, a __GFP_ZERO allocation will not be initialized.

... but the comment should be corrected too:
"Otherwise, a __GFP_ZERO allocation will trigger a memory corruption report
during unpoisoning."

Thanks.

> +	 */
> +	kernel_unpoison_pages(page, 1 << order);
> +
>  	/*
>  	 * As memory initialization might be integrated into KASAN,
>  	 * kasan_alloc_pages and kernel_init_free_pages must be
> @@ -2338,7 +2344,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>  	if (init && !kasan_has_integrated_init())
>  		kernel_init_free_pages(page, 1 << order);
>  
> -	kernel_unpoison_pages(page, 1 << order);
>  	set_page_owner(page, order, gfp_flags);
>  }
>  
>