linux-kernel - Re: [PATCH 33/43] kmsan: disable physical page merging in biovec

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Date:   Wed, 15 Dec 2021 14:17:09 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 33/43] kmsan: disable physical page merging in biovec

On Tue, Dec 14, 2021 at 05:20:40PM +0100, Alexander Potapenko wrote:
> KMSAN metadata for consequent physical pages may be inconsequent,

I think you mean 'adjacent'/ rather than 'consequent' here, i.e.

| KMSAN metadata for adjacent physical pages may not be adjacent

> therefore accessing such pages together may lead to metadata
> corruption.
> We disable merging pages in biovec to prevent such corruptions.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
> 
> Link: https://linux-review.googlesource.com/id/Iece16041be5ee47904fbc98121b105e5be5fea5c
> ---
>  block/blk.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/block/blk.h b/block/blk.h
> index ccde6e6f17360..e0c62a5d5639e 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -103,6 +103,13 @@ static inline bool biovec_phys_mergeable(struct request_queue *q,
>  	phys_addr_t addr1 = page_to_phys(vec1->bv_page) + vec1->bv_offset;
>  	phys_addr_t addr2 = page_to_phys(vec2->bv_page) + vec2->bv_offset;
>  
> +	/*
> +	 * Merging consequent physical pages may not work correctly under KMSAN
> +	 * if their metadata pages aren't consequent. Just disable merging.
> +	 */

Likewise here.

Mark.

> +	if (IS_ENABLED(CONFIG_KMSAN))
> +		return false;
> +
>  	if (addr1 + vec1->bv_len != addr2)
>  		return false;
>  	if (xen_domain() && !xen_biovec_phys_mergeable(vec1, vec2->bv_page))
> -- 
> 2.34.1.173.g76aa8bc2d0-goog
>